Optical code reading device with autofocussing

In a code reading device, which receives reflected light obtained by scanning a code represented on a recording medium with a laser light beam and decodes it to obtain the code, the reading probability is improved by varying the focusing position for every scanning period with the laser light beam.

FIELD OF THE INVENTION 
The present invention relates to a code reading device which scans codes 
recorded on a recording medium to output decoded signals, and in 
particular to a code reading device which can read out even if positional 
variations take place with respect to the recording medium. 
Further the present invention relates to a code reading device in which the 
reading operation is stabilized by preventing the destruction of a light 
emitting element constituting a light source for reading out the codes. 
Still further the present invention relates to a comparing and a holding 
circuit, which can effect surely the holding operation on the basis of the 
detection of the protecting function. 
Still further the present invention relates to a code reading device which 
scans and detects codes recorded in two-valued levels on the recording 
medium to improve the probability to read out rectangular signals 
alternating between the "H" and the "L" level, and which has a wide range 
for reading out. 
BACKGROUND OF THE INVENTION 
For goods, account books, cards, etc., which are present code recording 
mediums, information expressed by two magnetical or optical states is 
coded and recorded by combinations thereof. Representatives of these 
recorded codes and magnetic cards, and bar code labels, etc. can be cited. 
All of these codes are so constructed that various sorts of information 
are expressed by combining the two recorded states and decoded. For 
example, the bar code optically displayed on the surface of the medium of 
bar code labels, account books, etc. is expressed by the difference 
between two reflection coefficients of the ground color in the display 
region and the printed bar in the same region. A plurality of widths of 
the bars and the spaces in the bar code, which have a different reflection 
coefficient, express various sorts of coded information by their 
combinations. 
The bar code expressed optically is relatively simple with respect to 
account books or labels and is used frequently with a bar code printer for 
labels and account books, to print bar codes thereon at a place close to a 
job site. On the other hand, for a code reading device for reading out bar 
codes, for which the job sites of the reading operation are scattered, a 
portable hand wand type scanner disclosed e.g. in JP-B-63-60,435 
(JP-A-56-140,467; corresponding U.S. Pat. Nos. 4,387,297, 4,496,831 and 
4,593,186) is convenient. 
For detection of this kind of scanners there are the CCD light receiving 
type, the laser scanner type, etc., in which the medium is excited by 
irradiation light and having a detection position to where light reflected 
by the medium is forwarded. The reading characteristics of this kind of 
code reading devices are influenced by 3 factors including the state of 
the light emitting and the light receiving element in the code reading 
device, the state of operation from the light emitting and the light 
receiving element to the medium, and the state of representation on the 
medium. The hand wand type bar code scanner of the laser scanning type is 
popular because it can read out the bar code without contact and a bar 
code representation having a large width can be read out. 
In a bar code scanner using the method, by which the bar code is scanned 
with a laser beam to be read out. There is a mechanism called an 
autofocus, by which the focusing position of the optical system is 
variable, to improve operability by increasing the readable region. In 
this way a wider region is readable than with a fixed focus. 
A prior art technique using a laser scanner having such an autofocus 
mechanism will be explained below, referring to FIGS. 14 to 16. 
FIG. 14 is a perspective view illustrating the state where the bar code is 
read out by the laser scanner; FIG. 15 is a scheme showing the arrangement 
of various parts for explaining the reading resolving power of the laser 
scanner; and FIGS. 16(a) to 16(d) are schemes illustrating the reading 
operation of the laser scanner. 
In the figures reference numeral 801 is a laser scanner; 802 is a bar code 
representation; 8011 is a scanner case; 8012 is a semiconductor laser; and 
8013 is an optical system. 
As indicated in FIG. 14, the reading operation is effected by locating the 
laser scanner 801 so as to be opposite to the bar code representation 802. 
In the case where the optical system in the laser scanner 801 has a fixed 
focus, the laser scanner 802 and the bar code representation 802 should be 
located, opposite to each other so that the distance therebetween, i.e. 
the read distance D, is so set that the bar code representation 802 is 
located within the focus depth, i.e. the read distance. 
Such a laser scanner 801 is provided, as indicated in FIG. 15, with the 
semiconductor laser 8012 disposed in the scanner case 8011 thereof and the 
optical system (objective lens) 8013 for focusing the laser beam emitted 
by this semiconductor laser 8012. 
The laser beam emitted by this semiconductor laser 8012 is focused by the 
optical system 8013 at a focusing point 8013. The neighborhood of this 
focusing point F is a high resolution range, where fine codes can be read 
out, and with increasing distance from the focusing point F only codes of 
increasing size can be read out, from a middle resolution range to a low 
resolution range. 
With respect to this focusing point, the diameter of the laser beam is 
smallest at the focusing point and increases with increasing distance 
therefrom. 
As indicated in FIG. 16(a), the bar code recorded in the bar code 
representation 802, where the spot of the laser beam is formed, is 
expressed in a code by combining bars (black) and spaces (white). In the 
structure indicated in the figure the bar code is expressed in two-valued 
levels of narrow bar/wide bar and wide bar/wide space. As indicated in the 
figure, a void B, a deficiency C or dirt may exist, depending on the 
printing and the state of the surface of the medium. In the case where a 
bar code having such problems is scanned with the laser beam at a scan 
position CS indicated in the figure, a light reception signal obtained 
from the light receiving element is somewhat distorted, as indicated in 
FIG. 16(b), when the spot has a middle size, and when the size of the spot 
is smallest, the waveform varies due to the void B and the deficiency C, 
as indicated in FIG. 16(c). Further, when the size of the spot is great, 
the waveform varies, as indicated in FIG. 16(d), depending on the focused 
spot size, where it is extremely distorted so that the binary processing 
is difficult. In the case of this bar code representation correct decoding 
is possible in the state where the spot has a middle size, as indicated in 
FIG. 16(b). In the case where the size of the spot is smallest, as 
indicated in FIG. 16(c), the levels of the waveform corresponding to the 
positions of the void B and the deficiency C are lowered and shifts A and 
B are produced, which prevents correctly the bar code. Further, in the 
case where the spot has a great size, as indicated in FIG. 16(d), the 
ability to follow the bar code pattern and the output waveform is impacted 
on the whole so as to be dull, which makes the decoding operation 
extremely difficult. 
A scanner provided with an autofocus mechanism, which measures the distance 
between the medium and the scanner and adjusts the focusing point so as to 
be on the surface of the bar code representation, moves the optical system 
8013 on the basis of the measured distance and adjusts automatically the 
focus. 
A light reception signal obtained by the scanner is binary processed. The 
decoding processing is effected, as described in detail in Japanese in 
"Formation of Bar Code System", separate volume of Transistor Technique, 
Sensor Interfacing, No. 4, published by CQ Publishing Company, Jul. 1, 
1984, pp. 197 to 199. 
FIG. 17 is a circuit diagram showing the construction of the principal part 
of a semiconductor laser driving circuit of the coding device according to 
the prior art technique, in which De is a laser diode; 72 is an NPN type 
transistor driving the laser diode; 73 is a current limiting resistance; 
74 is controller; 75 is an NPN type transistor used for the operation of 
protecting the laser diode De; and 76 is an initiation detection section. 
In FIG. 17, the transistor 72 and the resistance 73, which control the 
driving current necessary for obtaining a predetermined light intensity 
from the diode De are connected in series with the laser diode De, and the 
output of the controller 74 for controlling this driving current is 
supplied to the base of the transistor 72 serving as the control terminal 
thereof. 
The intensity of the light emitted by the laser diode De is controlled by 
the intensity of the driving current corresponding to the value of the 
impedance between the collector and the emitter of the transistor 72, 
depending on the output value of the controller 74, to which an emitted 
light intensity setting signal is supplied from the exterior. 
However, with construction described above, the laser diode De can be 
destroyed by surge current produced at the switching-on of the power 
source. As a measure to prevent this the collector-emitter circuit of the 
transistor 75 for protecting is inserted in series in the series circuit 
consisting of the laser diode De, the collector-emitter circuit of the 
transistor 72 and the resistance 73, so that the time the power source is 
switched-on is detected and the impedance between the collector and the 
emitter of the transistor 75 is lowered relatively slowly in a 
predetermined time. In this way the driving current is increased gradually 
so as to delay the usual lighting operation so that a so-called slow start 
operation is effected. 
In this kind of code reading device, in the case where it is so constructed 
that the protecting operation for the semiconductor laser driving circuit 
is effected and the voltage varying, dependent on the environment, is 
compared with a reference voltage, the result obtained by the comparison 
being held, the circuit is so constructed that a device having the holding 
function such as a thyristor, a flipflop, etc. is connected with the 
output of a comparator effecting the operation of comparing the varying 
voltage with the reference voltage. 
Such a prior art comparator circuit with latch will be explained referring 
to FIG. 18. 
FIG. 18 is a scheme illustrating the construction of such a prior art 
comparator circuit with latch. 
In FIG. 18 reference numeral 51 is a comparator circuit; 52 is a thyristor 
circuit; 53 is an input terminal; and 54 is a reference voltage power 
source. 
The input voltage Vin to in the input terminal 53, which is the voltage to 
be compared, is applied to the non-inverting input terminal + of the 
comparator circuit 51 and compared with the reference voltage Vref of the 
reference voltage power source 54 applied to the inverting input terminal 
- of the comparator circuit 54. If the relation; 
EQU input voltage Vin&gt;reference voltage Vref 
is valid, the output voltage Vout from the output terminal of the 
comparator circuit 51 is changed to the "H" level and the output voltage 
Vout of "H" level is applied to the gate terminal of the thyristor 52 
through the current limiting resistance. In this way the impedance of the 
anode and the cathode of the thyristor 52 is turned on to a very low 
state. This state is held, until the voltage applied to the anode and the 
cathode of the thyristor 52 not shown in the figure is reset so that it is 
lowered to a value under a predetermined voltage. 
Further, in this holding structure, a flipflop circuit is disposed in lieu 
of the thyristor 52 so that the holding operation is effected according to 
the output voltage Vout of "H" level and that the holding state is reset 
by the reset terminal of the flipflop circuit. The protecting operation 
for the semiconductor laser illuminating the optical recording medium can 
be carried out by the operation for comparing, holding and resetting. 
In this kind of code reading device, because of fluctuations in the 
distance between the medium and the light receiving element and the angle 
corresponding to the operation state as well as the ground color and the 
reflection coefficient of the medium corresponding to the representation 
state, the detection light intensity arriving at the light receiving 
element varies significantly, which gives rise to undulations or 
differences in the height in the signal of amplitude obtained from the 
light receiving element. In order to obtain a rectangular pulse by 
amplifying this signal of amplitude for the purpose of the digital 
processing thereof, it is necessary to widen the dynamic range of the 
amplifying circuit. Amplifying circuits having a wide dynamic range there 
are generally known those effecting automatic gain control (AGC) and those 
effecting logarithmic curve amplification (Log AMP). These are not used in 
practice for the reason stated in the next paragraph, but since a 
measurement is taken by using the waveform processing such as a clamping 
circuit, the number of operations necessary for a success of the reading 
increases naturally and the recording state of the recording medium is 
restricted. 
However the prior art code reading device explained above, referring to 
FIGS. 14 to 16(d), has a problem that since it is so constructed that the 
focusing point is moved automatically on the basis of the distance between 
the recording medium and the scanner, in many cases the adjusted focusing 
point is not always in accordance with a readable position because of 
fluctuations in the state of representation of the code or the state of 
the surface of the recording medium. 
A first object of the present invention is, therefore, to provide a code 
reading device which can read the code at the adjusted focusing point and 
effect the reading in spite of fluctuations in the representation and the 
recording medium so that a high reading probability can be obtained. 
However the prior art code reading device explained above, referring to 
FIG. 17, has a problem that it is impossible to obtain any semiconductor 
laser driving construction which will work at a low power source voltage, 
because the transistor 72 for current driving the laser diode De, the 
transistor 75 for the protection operation and the current limiting 
resistance 73 are connected in series and therefore a power source 
voltage, which is higher by an amount twice as high as the voltage across 
the emitter-collector circuit, is required in the usual operation. 
A second object of the present invention is, therefore, to provide a code 
reading device having a semiconductor laser driving construction so formed 
that the destruction of the laser diode De is prevented. 
However in the prior art code reading device explained above, referring to 
FIG. 18, an inconvenience is produced, in the case where it is required to 
increase the integration density and to reduce the size, because devices, 
which are difficult to mount on an analogue IC or a small scale wiring 
board, such as thyristors, flipflops, etc. are used apart from the 
comparator for the purpose of holding the result of comparison by means of 
the comparator circuit 51. Further the circuit is complicated, because 
reset means for lowering the voltage between the anode and the cathode is 
required in the case where a thyristor is used, which is reset by 
turning-off, and the intensity of the conduction current between the anode 
and the cathode is so controlled that it is lower in the continuous 
holding state thereof than in the holding starting state. 
A third object of the present invention is, therefore, to provide a 
comparator circuit with a latch having a high integration density and a 
small size. 
However, in an amplifying circuit effecting the automatic gain control 
(AGC) described above, distortions are produced because the initial 
amplitude of the supplied detection signal corresponds to the rise of the 
represented code digital, which is not suitable for the detection and the 
processing of digital codes such as the bar code. Further in an amplifying 
circuit effecting the logarithmic curve amplification (Log AMP) described 
above, since the amplification characteristic curve is a logarithmic 
curve, if there are distortions in the supplied detection signal, the code 
reading device has a property that the reading is impossible in practice, 
which is basically unsuitable. 
A fourth object of the present invention is, therefore, to provide a code 
reading device in which the number of detecting operations is small and 
which can measure a wide representation state of the recording medium. 
SUMMARY OF THE INVENTION 
In order to achieve the first object described above, first technical means 
according to the present invention comprises a light emitting element for 
emitting a laser light beam, with which a code represented optically on a 
recording medium is irradiated; light emission driving means for supplying 
driving current for the purpose of making the light emitting element 
stated above emit the laser light beam; focusing point adjusting means for 
adjusting the focusing point of the laser light beam thus obtained, 
depending on the driving state of the light emission driving means; 
focusing point adjustment driving means for outputting a driving signal to 
move the adjusted position of the focusing point adjusting means stated 
above; optical deflection means for scanning the surface of the recording 
means stated above with the laser light beam stated above; deflection 
driving means for driving the deflection operation of the optical 
deflection means stated above; a light receiving element for receiving 
light reflected by the surface of the recording means stated above; 
decoding means for effecting the decoding operation on the basis of the 
output of the light receiving element stated above; and focusing point 
control means for outputting a control signal for moving the focusing 
point to the focusing point adjustment driving means stated above during a 
period of one deflection instruction of the optical deflection means 
stated above. 
In order to achieve the second object described above, second technical 
means according to the present invention comprises a laser diode De for 
outputting a laser light beam, depending on a current supplied by a power 
source Vcc; driving means 18 connected in series therewith for controlling 
current flowing through the laser diode De stated above; control means 300 
for supplying a control signal indicating conduction and interruption of 
the laser diode De to an input terminal B disposed in the driving means 18 
stated above; and initiation detection means 100 for detecting that the 
power source Vcc stated above and outputting a conduction starting signal 
preventing surge current to the laser diode De in a predetermined period 
of time to the control means 300. 
In order to achieve the third object described above, third technical means 
according to the present invention comprises an input terminal 53, to 
which a voltage to be compared Vin is applied; a comparator 51 having a 
reference input terminal -, to which a reference voltage Vref, with which 
the value of the voltage applied to the input terminal 53 is compared, is 
applied; a comparison input terminal +, to which the voltage to be 
compared from the input terminal 53 stated above disposed in the 
comparator 51 stated above is applied; an output terminal 56 disposed in 
the comparator 51 stated above for outputting a comparison output voltage 
Vout representing the maximum or the minimum, which is a result obtained 
by comparing the two voltages applied to the comparison input terminal + 
and the reference input terminal - stated above, respectively; positive 
feedback means 57, 59 supplying positive feedback current from the output 
terminal 56 to the comparison input terminal +; voltage dividing means 26, 
27, 58 for dividing a voltage to be compared Vin coming from the input 
terminal 53, which is applied to the comparison input terminal +, with 
which the positive feedback means 57, 59 stated above is connected; and 
reset means 8, Sr, 55, 60 connected with the reference input terminal - 
for removing the state where the positive feedback current is made flow 
through the positive feedback means 57, 59 and held by the fact that the 
value of the voltage supplied through the voltage dividing means 26, 27, 
58 stated above crosses the reference voltage Vref; wherein at least one 
of the positive feedback means 12, 57, 59 and the voltage dividing means 
26, 27, 58 is provided with rectifying means regulating the direction of 
current. 
In order to achieve the fourth object described above, fourth technical 
means according to the present invention comprises scan detection means 
for scanning and detecting periodically medium, in which codes represented 
by two states are recorded, with a sensor; amplifying means for amplifying 
the value detected by the scan detection means stated above to a 
predetermined level; amplification factor setting means for setting 
variably the amplification factor of the amplifying means stated above; 
selecting means for selectively specifying the value set by the 
amplification factor setting means stated above; selective control means, 
which selects a certain amplification factor in at least a period, during 
which the scan detection means stated above feeding the selecting means 
scans, and at the same time outputs a selection instructing signal for 
varying the amplification factor, responding to the period; waveform 
transforming means for transforming the output value of an amplification 
signal of the amplification factor setting means on the basis of the 
selection instructing signal of the selection control means stated above 
into a rectangular signal; and decoding means for decoding the rectangular 
signal coming from the waveform transforming means stated above, 
responding to the content of the record in the recording medium. 
The present invention provided with the first technical means described 
above works as follows. 
That is, a code reading device is provided, which has a wide reading region 
and an improved reading probability, even if the state of the recording 
medium fluctuates, because it is moved to the focusing position, where 
reading out is possible, depending on the representation state of the code 
and the state of the surface of the recording medium, due to the fact that 
it is moved to the focusing position for every scanning period, until the 
signal obtained by receiving light reflected by the code is decoded to 
obtain normal decoded data. 
The present invention provided with the second technical means described 
above works as follows. 
That is, a code reading device is provided, in which destruction of the 
laser diode De at a low power source voltage is prevented, because an 
emitted light intensity setting signal is cancelled by supplying a 
conduction starting signal to the control means 300, which signal 
increases gradually the intensity of the current from the initiation 
detection means 100 at switching-on the power source and the laser diode 
De is driven by driving means 18 according to the conduction starting 
signal. 
The present invention provided with the third technical means described 
above works as follows. 
That is, a code reading device is provided, in which the feedback current 
supplied from the output terminal 56 to the comparison input terminal + 
through the positive feedback means 12, 57, 59 according to the result of 
the inverted output of the comparator holds the output state of the output 
terminal 56 by giving forcedly a potential difference between the 
comparison input terminal + and the reference input terminal -, which 
constitutes a holding condition. At the same time this potential 
difference is continued to be held within a determined voltage region, 
owing to the fact that leak current is prevented by rectifying means 
provided at least in one of the positive feedback means 12, 57, 59 and the 
dividing means 26, 27, 58. This condition is surely returned to the usual 
comparison operation by the reset voltage applied to the comparison input 
terminal - from the reset means 8, Sr, 55, 60. In this way the circuit 
construction is simplified. 
The present invention provided with the fourth technical means described 
above works as follows. 
That is, a code reading device is provided, in which no special skill is 
required for the detection operation and which can deal with a relatively 
wide recording state of the medium, because the decoding is effected with 
an amplification factor, with which decipherable rectangular signal is 
obtained, among a plurality of scannings, due to the fact that the 
amplification factor is kept to be constant during one period of the 
reading scanning and the amplification is effected with an amplification 
factor varied when the procedure proceeds to the next period, while a 
plurality of reading scannings are effected by one operation.

DETAILED DESCRIPTION 
Hereinbelow a first embodiment of the present invention having the first 
technical means will be explained in detail, referring to FIGS. 1 to 7. 
FIG. 1 is a block diagram showing the outline of the construction for 
explaining the first embodiment of the present invention, in which 
reference numeral 1 is a control circuit; 2 is a light emission control 
section; 3 is a light emission driving circuit; 4 is a deflection control 
section used in a deflecting device; 5 is a deflection driving circuit; 6 
is a focus adjusting control section used in a focus adjusting device 
(voice coil motor); 7 is a focus adjusting drive circuit; 8 is a 
preamplifier; 9 is an amplifying circuit; 10 is a binary coding circuit; 
11 is a decode section; 12 is a light emitting laser element; 13 is a 
focus adjusting device constructed e.g. by the voice coil motor; 14 is a 
focus adjusting lens; 15 is a holed mirror; 16 is a light receiving 
element; 17 is a fixed lens; 18 is a reflecting mirror; 19 is a galvano 
scanner; 20 is a bar code representing surface; 21a and 21b are switches 
Sw 1 and Sw 2, respectively; and 22 is an output terminal to a host 
computer. Further a photo-electric converting section is composed of the 
light emission driving circuit 3, the light emitting laser element 12, a 
light receiving element 16 and a preamplifier 8. Still further the 
deflecting device is composed of the reflecting mirror 18 and the galvano 
scanner 19. 
In the figure a laser light beam is emitted by the light emitting laser 
element 12 energized by the light emission driving circuit 3, driven by 
the light emission control section 2. The laser light beam passes through 
the hole formed in the holed mirror 15 and collected by the fixed lens 17. 
Then the path thereof is deflected by the reflecting mirror 17 and it 
arrives at the bar code representing surface 20. 
The reflecting mirror 18 sweeps the laser light beam in a one-dimensional 
direction by the deflection scanning by means of the galvano scanner 19. 
The bar code is scanned therewith and the reflected light is projected to 
the light receiving element 16 through the reflecting mirror 18 and the 
fixed lens 17. 
The galvano scanner 19 is driven by a driving signal from the deflection 
driving circuit 5 on the basis of a signal from the deflection control 
section 4. 
The reflected light from the bar code, which is received by the light 
receiving element 16, is converted by the photo-electric converting 
section 23 into an electric signal, which is outputted to the amplifying 
circuit 9 through the preamplifier 8. This signal is given to the binary 
coding circuit 10, after having been amplified to a predetermined level in 
this amplifying circuit. 
The binary coding circuit 10 transforms the input signal into a two-valued 
signal, which is supplied to the decode section 11. A signal thus obtained 
by decoding (decode data) is transmitted to the host computer (not shown 
in the figure) through the terminal 22. 
In this case, since the distance between the light emitting laser element 
12 and the bar code representing surface 20 is not fixed, in the case 
where the optical system of the scanner has a fixed focus, the focusing 
point should be adjusted by moving the scanner or the bar code medium. 
The device indicated in the figure is so constructed that this focus 
adjustment is effected automatically. That is, the focus adjusting device, 
which is an actuator called a voice coil motor, producing moving force 
making the focus adjusting lens 14 move forward and backward, is mounted. 
In this way the focus adjusting lens 14 is moved forward and backward in 
the axial direction of the optical system. depending on the distance 
between the light emitting laser element 12 and the bar code representing 
surface 20. 
The movement of this focus adjusting lens 14 is effected by the fact that 
the focus adjusting drive section 7 gives the focus adjusting device 13 
driving current, receiving the driving signal produced by the focus 
adjusting control section 6 based on the control signal of the control 
circuit 1. 
Further the deflecting device sweeps the laser light beam in a 
one-dimensional direction in the direction, in which the galvano scanner 
19 scans the bar code on the bar code representing surface 20 by means of 
the reflecting mirror 18 and it is driven by the deflection driving 
circuit 5 inputting the driving signal of the deflection control section 
4. 
The switches Sw 1 and Sw 2 are a two-step switch operated by a user. A 
first step operation switches-on the switch Sw 1 (21a) and supplies a 
driving signal to the light emission driving circuit 2, which makes the 
light emitting laser element 12 emit the laser light beam and at the same 
time drives the deflection control section 4 and the deflection driving 
circuit 5 so as to scan the bar code representing surface with the laser 
light beam. 
Then a second step operation switches-on the switch Sw 2 (21b) and moves 
the focus adjusting lens 14 by means of the focus adjusting device 13 
through the focus adjusting control section 6 and the focus adjusting 
drive section 7 so as to effect the focus adjustment. 
The focus adjusting control section 6 generates successively stepwise 
continuous driving signals or stepwise driving signals, e.g. driving 
signals of 10 steps. The focus adjusting drive section 7 drives the focus 
adjusting device 13 by using these driving signals so as to move 
continuously or stepwise the focus adjusting lens 14 forward and backward 
along the optical axis. 
In the course of the movement of the focus adjusting lens 14, the bar code 
indicated on the bar code representing surface 20 is irradiated with the 
laser light beam and the reflected light is collected on the light 
receiving element 16 through the reflecting mirror 18, the fixed lens 17 
and the holed mirror 15 to be converted there into an analogue signal. 
This analogue signal is amplified to a predetermined level by the 
amplifying circuit 9, after having been preamplified by the preamplifier 
8, and inputted to the binary coding circuit 10. 
The binary coding circuit 10 converts the amplified analogue signal into a 
two-valued signal and gives it to the decoding section 11, in which the 
signal is decoded. In the case where it is correctly decoded there, the 
decode data are transmitted to the host computer through the terminal 22. 
When it is correctly decoded in the decoding section 11, the decoding 
section 11 gives the control circuit 1 a signal indicating that the 
decoding has been effected correctly. 
When the control circuit 1 receives the signal described above from the 
decoding section 11, it stops the operations of the light emission driving 
circuit 3 and the deflection control section through the light emission 
control section 2 to execute instructions to stop the emission of the 
laser light beam and to stop the swing of the reflecting mirror 18 by 
means of the galvano scanner 19. 
At the same time the control circuit 1 stops the driving operation of the 
focus adjusting control section 6 and issues an instruction to stop the 
focus adjusting operation of the focusing adjusting lens 14 by means of 
the focus adjusting device 13. 
As operation method for the focusing adjustment, there are known a 
plurality of methods as explained in detail, referring to FIGS. 2 to 7. 
The parts and the functions, which are identical to those explained, 
referring to FIG. 1, are indicated by the same or relating reference 
numerals and detailed explanation thereof will be omitted. 
At first, FIG. 2 is a scheme illustrating the construction, which is an 
example of the laser scanner, in which the focus adjusting lens is moved 
continuously. 
In FIG. 2, reference numeral 111 is a decode circuit; 112 is an output 
circuit; 201 is an off signal generating circuit; 202 is a counter 
circuit; 203 is a constant memory; and 204 is a comparator. 
The decode section 11 consists of the decode circuit 111 and the output 
circuit 112, which outputs a decode signal dt on the basis of the decoded 
signal dc constituted by character data and error data outputted by this 
circuit 11 and at the same time gives the control circuit 1 a decode 
termination signal off on the basis of the character data outputted by the 
circuit 11. 
The focus adjusting lens 14 moves non-stepwise and continuously the focus 
from the nearest position to the farthest position and sets the optimum 
focusing point, where the probability of the success is greatest, so that 
it is located at the middle point between the nearest position and the 
farthest position, in the case where the interval in the arrangement 
between the laser scanner and the bar code representing surface 20. This 
movement from the nearest position to the farthest position of the focus 
is effected with the speed and the number of scannings previously set, 
corresponding to the greatest number of scannings with the deflecting 
device 18, 19. The device is so constructed that the movement of the focus 
adjusting lens 14 is stopped, when the decoding is terminated or when the 
deflecting device 18, 19 has scanned the bar code the greatest number of 
times of scannings. 
The deflection control section 4, to which a scanning instruction signal s1 
from the control circuit 1 to start the scanning resets the count number 
of a counting circuit 202 to its initial value and at the same time 
outputs a drive instruction signal for making the deflection drive circuit 
5 supply a deflection driving signal bi to make the deflecting device 18, 
19 effect an oscillation operation. 
During a period of time where the deflection driving signal bi is supplied, 
the deflecting device 18, 19 scans the bar code representing surface 20 
with the laser light beam by means of the reflecting mirror 18. In order 
to obtain this number of scannings, the number of deflecting movements of 
a pivoting shaft, not shown in the figure, disposed in the galvano scanner 
19 is detected and pulse-shaped pivoting movement detecting signals eg are 
counted by the counting circuit 202. The count number cn of the counting 
circuit 202 is compared with a stored value cs in the comparator 204, 
which corresponds to the greatest number of pivoting movements of the 
galvano scanner 19, which is previously set and stored in the constant 
memory 203, for every scan instructing signal s1, and when it is judged 
that the following formula; 
EQU cn.gtoreq.cs 
is valid, the off signal generating circuit 201 supplies an operation stop 
instructing signal off to each of the circuits of the light emission 
control circuit 2, the deflection driving circuit 5 and the focus 
adjusting drive circuit 7. Each of the circuits, to which this operation 
stop instructing signal off is supplied, is constructed so as to interrupt 
the deflection driving signal bi, the light emission driving signal oe and 
the focus adjusting drive signal fc. Further this pivoting movement 
detection signal eg is supplied also to the light emission control section 
2. 
The light emission control section 2, to which a light emission instructing 
signal s2 for making it be ready for the laser light beam emitting 
operation is supplied from the control circuit 1 at the same time as the 
output of the scan instructing signal s1, which makes the galvano scanner 
19 pivot, continues to supply the stop instructing signal to the light 
emission driving circuit 3 for making it stop the light emitting 
operation, until the first pulse of the pivoting movement detection signal 
eg, which the galvano scanner 19 outputs. The light emission control 
section 2, to which the first pulse of the pivoting movement detection 
signal eg is supplied, just after the reflecting mirror 18 has begun to 
start the pivoting movement, outputs the light emission driving signal oe 
to the light emission driving circuit 3 to energize the light emitting 
laser element 12 and to excite the laser light beam. This is because in 
the state where the reflecting mirror 18 is not rotated or in the case 
where the speed of the rotation thereof is lower than a predetermined 
value, the linear speed of the movement of the spot of the projected laser 
light beam is low and it is necessary to effect a protecting operation to 
prevent accident that a same place on a human body such as an eye is 
irradiated with the laser light beam during a long period of time. 
The light emission control section 2, to which this pivoting movement 
detection signal eg is supplied, stops the laser light beam emitting 
operation, in the case where no pulse of the pivoting movement detection 
signal eg is supplied during a period of time corresponding to a number of 
times, which is set so as to be e.g. 2 to 8 times as great as the number 
of times the galvano scanner 19 is to pivot per unit time so that the 
linear speed of the movement of the spot of the projected laser light beam 
is lowered and the protecting operation is effected to prevent accident 
that a same place on a human body such as an eye is irradiated with the 
laser light beam. 
The light emission control section 2, to which the operation stop 
instructing signal off outputted by the off signal generating circuit 201 
is supplied, supposes that no reading of the bar code to be detected has 
been effected during the period of time corresponding to the greatest 
number of scannings and stops the laser light beam emitting operation. 
Information of the analogue signal coming from the light receiving element 
16 in the photo-electric converting section 23 through the preamplifier 8 
is transmitted to the amplifier circuit 9 and the binary coding circuit 10 
in this order and a two-valued signal di and supplied to the decoding 
circuit 111. 
When the switch Sw 2 (21b) is turned on by the second step operation, after 
the switch Sw 1 (21a) has been turned on by the first step operation, the 
focus adjusting control section 6, to which a focus adjust instructing 
signal s3 is supplied from the control circuit 1, is so constructed that a 
drive instructing signal for moving the focus adjusting device 13 with 
predetermined speed and direction is supplied to the focus adjusting drive 
circuit 7. The focus adjusting drive circuit 7 moves the focus adjusting 
device 13, on which the focus adjusting lens 14, according to a supplied 
focus adjusting drive signal fc and stops the moving operation of the 
focus adjusting device 13 in synchronism with the supply of the movement 
stop instructing signal off, even in the state where the focus adjusting 
drive signal fc. The focus adjusting device 13 moves slowly and 
continuously with a speed within a tolerated speed region, with which it 
moves once forward and backward during a period of time corresponding to 
the greatest number of times of pivoting movements of the galvano scanner 
19. This movement direction is so set that the forward and backward 
movement is effected around the optimum focusing point described above, 
using it as the reference position. In the case where the movement stop 
instructing signal off is supplied, the focus adjusting device 13 is 
stopped in the neighborhood of the optimum focusing point. However, even 
in the state where the focus adjustment instructing signal s3 is 
interrupted by a decoding termination signal off of the output circuit 112 
and it is stopped at a not specified position, it is moved in a 
predetermined direction previously set, after it has been returned to the 
optimum focusing point by inputting again the focus adjustment instructing 
signal s3. 
Further it is a matter of course that the scanning instructing signal s1, 
the light emission instructing signal s2 and the focusing adjustment 
instructing signal s3 described above outputted by the control circuit 1 
may be replaced by one corresponding to the scanning instructing signal s1 
and the light emission instructing signal s2 and another corresponding to 
the focusing adjustment instructing signal s3. However it may be so 
constructed that the three signals are unified to one and only one 
operation switch is used to adjust the focusing point. 
Hereinbelow, referring to FIG. 3, another example of the laser scanner, 
which is so constructed that the focusing point is adjusted continuously, 
as explained, referring to FIG. 2. The parts and the functions indentical 
to those explained, referring to FIGS. 1 and 2, are indicated by the same 
or relating reference numerals and therefore explanation thereof will be 
omitted. 
The pivoting movement detection signal eg, which is outputted in the form 
of a pulse for every deflection of the deflecting device (18, 19), is 
supplied to the decoding circuit 111. This decoding circuit 111, to which 
this pivoting movement detection signal eg is supplied, resets the 
preceding decoding operations and begins to decode the two-valued signal 
di succeedingly supplied. 
Further, instead of disposing the off signal generating circuit 201 
indicated in FIGS. 2 and 3 described above, the device may be so 
constructed that a signal off for setting the number of scanning 
detections from an external device (e.g. host computer, etc.) is supplied 
to each of the circuits. 
Hereinbelow an example of the laser scanner, which is so constructed that 
the focusing point is adjusted step by step according to the number of 
scannings of the deflecting device will be explained by using the 
construction scheme indicated in FIG. 4. The parts and the functions 
identical to those explained, referring to FIGS. 1 to 3, are indicated by 
the same or relating reference numerals and therefore explanation thereof 
will be omitted. 
FIG. 4, reference numeral 202 is a first counting circuit; 203 is a first 
constant memory; 204 is a first comparator; 401 is an OR circuit; 402 is a 
commutator; 403 is a second counting circuit; and 404 is a second constant 
memory. 
The off signal generating circuit 201, to which the pivoting movement 
detection signal eg outputted in the form of a pulse, accompanying the 
pivoting movement of the galvano scanner 19 serving as the deflecting 
device, is supplied, compares the count number cn1 of the first counter 
202 with the value cs1 stored in the first constant memory 203, 
corresponding to the greatest number of pivoting movements of the scanner 
19 for every scanning instructing signal s1 in the first comparator 204 
and in the case where it is judged that the condition expressed by the 
following formula; 
EQU cn1.gtoreq.cs1 
is fulfilled, it supplies the movement stop instructing signal off to the 
light emission control section 2 and the deflection driving circuit 5. 
The second counter circuit 403, to which the pivoting movement detection 
signal eg of the deflecting device 18, 19 is supplied, effects a counting 
operation similarly to the first counter 202. The second counter circuit 
403, to the reset terminal of which the output of the OR circuit 401' is 
supplied, resets the counting operation by means of a reset signal p in 
synchronism with either one of a focus change instructing signal cp 
outputted by the second comparator 405 and a drive instructing signal, 
which the deflection control section 4 outputs in synchronism with the 
supply of the scanning instructing signal s1. The second counter circuit 
403, to which the pivoting movement detection signal eg is supplied, gives 
the second comparator 405 the count number cn2. The second comparator 405, 
to which this count number cn2 as well as the stored value cs1 in the 
second constant memory 404 set previously by a value m/n obtained by 
dividing the greatest number of pivoting movement m of the galvano scanner 
19, which is the stored value cs1 in the first constant memory 203, by a 
positive integer n (n=1, 2, 3, . . . , n) excluding 0, supplies a focus 
change instructing signal cp to the focus adjusting drive circuit 7 and to 
one of the input terminal of the OR circuit 401, if a condition expressed 
by the following formula; 
EQU cn2.gtoreq.cs2 
is fulfilled. 
The focus adjusting drive circuit 7, to which the focus change instructing 
signal cp is supplied for every number (m/n) of pivoting movements of the 
galvano scanner 19 supplies the focus adjusting drive signal fc in order 
that the focus adjusting device 13 moves step by step the focus adjusting 
lens 14. The focus adjusting device 13 moves the focus adjusting lens 14 
for every number (m/n) of pivoting movements (e.g. once for one pivoting 
movement of the galvano scanner 19) to a new focusing position set 
stepwise by the focus adjusting drive signal fc. 
The focus adjusting drive signal fc varying stepwise is supplied also to 
the commutator 402. Thus the device is so constructed that the analogue 
signal es supplied to the amplifying circuit 8 is interrupted only during 
the period of time previously set corresponding to the termination of the 
movement of the focus adjusting lens 14 according to the stepwise 
variation of the focus adjusting drive signal fc. 
The pivoting movement detection signal eg is also supplied to this 
commutator 402. As far as the amount of variations in the linear speed set 
according to the decoding capacity of the decoding circuit 111, with which 
the reflecting mirror 14 scans the bar code representing surface 20, is 
within a tolerated region (i.e. within a predetermined width measured from 
the center of the pivoting movement), the commutator 402 supplies the 
analogue signal es to the amplifying circuit 8. When it is outside of the 
tolerated region (i.e. within predetermined widths measured from the two 
extremities of the pivoting movement towards the center), it executes a 
switching operation to interrupt the analogue signal es to the amplifying 
circuit 8. Consequently the circuits succeeding the amplifying circuit 8 
effect a series of decoding operations only under the condition of time 
where the amount of variations in the linear speed of the scanning is 
within the tolerated region and the focusing position is stable. 
Hereinbelow another example of the laser scanner constructed so as to 
adjust step by step the focusing position according to the number of 
scannings of the deflecting device will be explained, referring to the 
construction scheme indicated in FIG. 5. The parts and the functions 
identical to those explained, referring to FIGS. 1 to 4, are indicated by 
the same or relating reference numerals and therefore explanation thereof 
will be omitted. 
The difference of the device indicated in FIG. 5 differs from that 
indicated in FIG. 4 is that the pivoting movement detection signal e.g. 
according to the number of pivoting movements of the galvano scanner 19 of 
the deflecting device is supplied to the reset terminal of the decoding 
circuit 111. When the pivoting movement detection signal e.g. is supplied 
to the decoding circuit 111, all the decoding operations, which are in 
course of execution, are cancelled and the decoding circuit 111 begins to 
decode the data obtained by transforming the analogue signal e.g. 
outputted after the supply of the pivoting movement detection signal e.g. 
into a two-valued signal. That is, this reset operation is so effected 
that a set of two-valued signals di, for which the decoding operation is 
not terminated before the supply of the pivoting movement detection signal 
e.g., is cleared, supposing that no normal bar code has been read out and 
that an encoding processing for a pulse train of the two-valued signal di 
supplied succeedingly is effected for every reading scanning. 
Still another example of the laser scanner constructed so as to adjust step 
by step the focusing position according to the number of scannings of the 
deflecting device will be explained below, referring to the construction 
scheme indicated in FIG. 6. The parts and the functions identical to those 
explained, referring to FIGS. 1 to 5, are indicated by the same or 
relating reference numerals and therefore explanation thereof will be 
omitted. 
The decoding circuit 111 in the state where the first two-valued signal di 
is not decoded even after the passage of a period of time set previously 
corresponding to the scanning speed of the deflecting device 18, 19 
cancels automatically all the data, which have been supplied up to this 
moment, to reset the circuit to its initial state and at the same time 
supplies a focus change instructing signal fail to the focus adjusting 
drive circuit 7. Every time a focus change instructing signal fail is 
supplied, the focus adjusting drive circuit 7 supplies a focus adjust 
driving signal fc varying stepwise for specifying the amount of 
displacement previously set and its direction to the focus adjusting 
device 13 and the commutator 402 to execute the focus change procedure. 
Still another example of the laser scanner constructed so as to adjust step 
by step the focusing position according to the number of scannings of the 
deflecting device will be explained below, referring to the construction 
scheme indicated in FIG. 7. The parts and the functions identical to those 
explained, referring to FIGS. 1 to 6, are indicated by the same or 
relating reference numerals and therefore explanation thereof will be 
omitted. 
Different from the construction indicated in FIG. 6, the pivoting movement 
detection signal e.g. is supplied to the reset of the decoding circuit 111 
and the device is so constructed that the focus change instructing signal 
fail is supplied to the focus adjusting derive circuit 7 only in the state 
where the decoding operation is not terminated and the pivoting movement 
detection signal e.g. is supplied. 
The devices indicated in FIGS. 6 and 7 described above are so constructed 
that the focusing position is changed, in the state where the decoding 
operation cannot be terminated and no decoding signal dt can be obtained 
in a predetermined period of time. On the contrary, in the case where a 
decoding signal dt is obtained in a predetermined period of time, the 
focusing point at the reading scanning, where the decoding signal dt has 
been obtained, is kept, as it is, in the following reading scanning by the 
fact that the scanning instructing signal s1 and the light emission 
instructing signal s2 are supplied successively. 
According to this method, in the case where a number of bar codes are read 
out one after another, an operator can read them rapidly from experience 
without varying significantly the distance between the bar code scanner 
and the recording medium, on which the bar code is represented. 
In this way, when successive bar codes are read out, if the position of the 
focus doesn't vary, the operation can be terminated more rapidly. 
The focusing position adjusting operation explained above is effected not 
always when the projected spot is formed most sharply, but in the state 
where deficiencies or dirty are produced in the bar code representation, 
the optimum reading position can take place, when the projected spot is in 
a defocused state. Differing from the auto focus mechanism, for which the 
focusing position is the optimum position, the device according to the 
present invention has no complicated structure for detecting the position 
of the recording medium, owing to the fact that the focusing position is 
moved successively in the state where the decoding is possible even in the 
defocused state. 
Further more it is a simple modification for those skilled in the art to 
achieve extremely easily that the construction for the focus adjustment 
explained above may be located in front of the light receiving element. 
Hereinbelow a second embodiment of this invention having the second 
technical means will be explained in detail, referring to FIG. 8. 
FIG. 8 is a circuit diagram illustrating the construction of the circuit 
according to the present invention, which can be used in the code reading 
device by optical reading. 
In the figure reference numerals 1, 3, 5, 6, 7, 9, 14, 15, 19, 21, 25, 26 
are resistances; 2, 16, 24 are capacitors; 4, 8, 18, 20, 27 are NPN type 
bipolar transistors; 10, 11 are two-terminal-input type operational 
amplifiers; 12, 13 are diodes; 17 is a monitor diode incorporation type 
light emitting diode unit; 22 is a temperature detecting thermistor; 23 is 
a Zener diode; De is a laser diode; Dm is a photo-diode; 100 is an 
initiation detecting section; 200 is an operation detecting section; 300 
is a control section; and 400 is an operation voltage generating section. 
At first, the construction of the device will be explained. In the light 
emitting diode unit 17 there are disposed the laser diode De for 
irradiating the optical recording medium with a laser light beam and the 
PIN type photo-diode Dm for monitoring the intensity of the light emission 
of this laser diode De. It is so constructed that the cathode of the 
photo-diode Dm is connected with the anode of the laser diode De. The 
power source voltage Vcc is applied to the connection of the anode of the 
laser diode De with the cathode of the photo-diode Dm. The anode of the 
photo-diode Dm is connected with the comparison input point B for 
effecting the control of the intensity of the light emission of the laser 
diode De disposed in the control section 300 explained later. The cathode 
of this laser diode De is connected with the collector of the driving NPN 
type transistor 18 for controlling the current flowing through the laser 
diode De. The emitter of this transistor 18 is grounded through the 
resistance 19 for detecting the intensity of the conduction current of the 
operation detecting section 200 explained later. The base of this 
transistor 18 is constructed as an instruction signal input point E, to 
which a protection instruction and conduction current intensity 
instruction outputted by both the operation detecting section 200 
described later and the control section 300. On the other hand the laser 
diode De is so constructed that heat produced by the laser diode De, 
through which current flows, is transferred to the thermistor 22 for 
detecting the temperature. The power source voltage Vcc is applied through 
the resistance 21 to an end of this thermistor 22. The connection of this 
thermistor 22 with the resistance 21 is grounded through the Zener diode 
23, whose cathode is connected therewith for generating a constant 
voltage, and the capacitor similarly for bypassing alternating current 
component, which are connected in parallel. The other end of the 
thermistor 22 is grounded through the resistance 26 disposed on the 
operation detection section 200 described later for detecting the 
intensity of the current flowing therethrough, which increases with 
increasing temperature of the thermistor 22. 
In the initiation detecting section 100 the resistance 1 and the capacitor 
2 are connected in series between the power source terminal Vcc, with 
which the positive pole of the power source voltage Vcc is connected, and 
the common ground line GND, with which the negative pole of the power 
source voltage Vcc is connected. The base of the NPN type transistor 4 is 
connected with the common connecting point A between this resistance 1 and 
the capacitor 2. The emitter of this transistor 4 is grounded and the 
collector thereof is connected with an end of the resistance 3. The power 
source voltage Vcc is applied to the other end of this resistance 3 
through the resistance 5 set to a value extremely high with respect to the 
value of the resistance 3. The connection between the resistances 5 and 3 
constitutes the output terminal of the initiation detecting section 100. 
These are constructed so as to output an initiation judging signal, which 
decreases relatively slowly, for preventing the destruction accident of 
the laser diode De at the switching on of the power source Vcc, by the 
fact that the value of the voltage applied to the comparison input point B 
in the control section 300 described later is raised to the value of a 
voltage, which is extremely close to the power source voltage Vcc, only 
during a period of time determined depending on the time constant of the 
resistance 1 and the capacitor 2, starting from the point of time where 
the power source voltage Vcc is turned on. 
The bases of the NPN type transistors are connected with the connection of 
the resistance 19 in the operation detection section 200 with the emitter 
of the transistor 18 and the connection of the resistance 26 with the 
thermistor 22, respectively. The power source voltage Vcc is applied to 
the collectors of these transistors 20 and 27 through the resistance 25 
for pull-up and both the emitters thereof are grounded. This circuit is so 
constructed that the connection F of the collectors of these transistors 
20 and 27 with the resistance F supplies an anormality detection signal to 
the non-inverting input terminal + of the operational amplifier 11, which 
anormality detection signal is of "L" level, when an excessively high 
intensity of the current increasing with excessive increase of the current 
flowing through the laser diode De and with temperature rise of the 
thermistor 22 is found. The operational amplifier 11, to which the 
anormality detection signal of "L" level is supplied, is constructed so as 
to act as a comparator with latch holding the output state of "L" level, 
until it is reset. The anode and the cathode of the diode 12, through 
which the positive feedback current flows, are connected with the 
non-inverting input terminal + and output terminal of this operational 
amplifier 11, respectively. The value of the reference voltage Vref 
indicating the threshold value, which is the limit of the normal operation 
of the laser diode De, from the operation voltage generating section 400 
described later and the value of the reset voltage Vs from the transistor 
8 stated later are supplied to the inverting input terminal - of this 
operational amplifier 11. The cathode of the diode 13 preventing to 
transmit the "H" level of this output terminal to the instructing signal 
input point E is connected with the output terminal of this operational 
amplifier 11. The anode thereof is connected with one end of the 
resistance 15 limiting the intensity of the current flowing therethrough, 
when the output terminal of the operational amplifier is at the "L" level, 
and the other end is connected with the instructing signal input point E, 
which is the base of the transistor 18. The circuit is so constructed that 
the current flowing through a series circuit consisting of this resistance 
15 and the diode 13 serves as the protection instructing signal for 
cancelling the current intensity instructing signal applied from the 
control section 300 to the instructing signal input point E, owing to the 
fact that the value of the voltage to be compared Vin corresponding to the 
voltage drop across the resistances 20 and 27 serving as a signal source 
exceeds the value of the voltage Vbe, at which the current begins to flow 
in the forward direction between the base and the emitter of the 
transistors 20 and 27, and at this time the value of the voltage at the 
connection F between the transistors 20 and 27 having the rectifying and 
the voltage dividing function and effecting the detection operation 
becomes once lower than the value of reference voltage Vref applied to the 
operational amplifier 11 so that the output terminal of the operational 
amplifier 11 is held at the "L" level, only until the value of the reset 
voltage Vs is applied to the inverting input terminal - of the operational 
amplifier 11. 
The operational amplifier 10 in the control section 300 is constructed so 
as to work as a comparator, which outputs the "H" level, when the value of 
the voltage applied to the comparison input point B of the control section 
300, where the initiation detecting signal is applied to the inverting 
terminal - of the operational amplifier 10, connected with the anode of 
the photo-diode Dm as well as the resistances 3 and 5 exceeds the value of 
the reference voltage applied from the operation voltage generating 
section 400 stated later to the non-inverting input terminal + of this 
operational amplifier 10, and the "L" level, when the former becomes lower 
than the latter. The output terminal of the operational amplifier 10 is 
grounded through the resistance 14 and the capacitor 16. The connection E 
of the resistance 14 with the capacitor 16 in the control section 300 is 
connected with the base of the transistor 18 driving the laser diode De. 
The series circuit consisting of the resistance 14 and the capacitor 16 is 
constructed as an integrating circuit outputting a value of a DC voltage 
proportional to the ratio in time, with which the output terminal of the 
operational amplifier 10 outputs the "H" level. 
In the operation voltage generating means 400 a series circuit consisting 
of the resistance 6, the resistance 8 and the resistance 8 is connected 
between the voltage source Vcc and the ground line GND. It is so 
constructed that the value of the voltage indicating the intensity of the 
light emitted by the laser diode De is supplied from the connection C 
between the resistance 6 and the resistance 7 to the non-inverting input 
terminal + of the operational amplifier 11 and that the value of the 
voltage indicating the holding and releasing operation is supplied from 
the connection G between the resistance 7 and the resistance 8 to the 
inverting input terminal - of the operational amplifier 11. The collector 
of the transistor 8 for the reset is also connected with this connection 
G. The emitter of this transistor 8 is grounded. As far as a reset signal 
of "H" level is applied to the base of the transistor 8, the collector and 
the emitter of the transistor 8 are in the low impedance state. As far as 
a reset signal of "L" level is applied to the base of the transistor 8, 
the value of the reference voltage Vcf indicating the center value of the 
intensity of the light emitted by the laser diode De is outputted from the 
connection C and the value of the reference voltage Vref indicating the 
threshold value of the holding operation of the operational amplifier 11 
is outputted from the connection D. As far as a reset signal of "H" level 
is applied to the base of the transistor 8, a value of the voltage Vcr 
indicating an intensity of the light emission lower than the central value 
of the intensity of the light emitted by the laser diode De is outputted 
from the connection C and a value of the reset voltage Vs indicating the 
releasing operation of the holding state of the operational amplifier 11 
is outputted from the connection G. 
Hereinbelow the operation of the construction described above will be 
explained. 
At first, when the power source of the code reading device is switched on, 
the potential at the non-inverting input terminal + (connection C) of the 
operational amplifier 10 arrives at the same time as the switch-on of the 
power source Vcc at the value of the reference voltage Vcf indicating the 
central value of the intensity of the light emitted by the laser diode De, 
expressed by the following equation; 
EQU Vcf=Vcc.multidot.(R7+R9)/(R6+R7+R9) 
On the contrary, the potential at the inverting input terminal - 
(connection B) of the operational amplifier 10 rises according to 
predetermined characteristics together with the potential of the 
connection A, which rises with a certain time constant determined by the 
time constant circuit consisting of the resistance 1 and the capacitor 2 
and an initiation judging current Isd flows through the path of power 
source Vcc .fwdarw. resistance 5 .fwdarw. resistance 3 .fwdarw. from 
collector to emitter of the transistor 4 .fwdarw. ground line GND with the 
rising potential at the connection A. This initiation judging current Isd 
charges the capacitor 2 and increases relatively slowly, corresponding to 
the base current Ibe4, which is made flow by the fact that the voltage 
Veb4 applied between the base and the emitter of the transistor 4 arrives 
at a predetermined value (e.g. + 0.06 V), until it is saturated, depending 
on the resistance 1 and the current amplification factor h.sub.fe of the 
transistor 4. The potential at the connection B, which rises according to 
the increasing characteristics of the intensity of this base current Ice4 
descends to a potential, obtained by dividing the power source voltage by 
the resistance 5 set to a relatively high resistance value on one side and 
the resistance 3 set to a relatively low resistance value and the circuit 
between the collector and the emitter of the transistor 4 on the other 
side, which is somewhat lower than the value of the reference voltage Vcf 
at the connection C. Corresponding thereto, the potential at the 
connection E rises to a value of the voltage, with which a value of the 
driving current giving rise to an intensity of light somewhat higher than 
the central value of the light intensity emitted by the laser diode De by 
the fact that the ratio in time, with which the "H" level signal is 
outputted from the output terminal of the operational amplifier 10, 
increases gradually. Consequently the intensity of the driving current 
flowing through the laser diode De rises not rapidly at the switch-on of 
the power source and thus a so-called soft start is effected so that the 
intensity of the emitted light rises with an appropriate speed, until an 
intensity of emitted light arrives at a predetermined value. 
The intensity of the light emitted by the laser diode De is detected by the 
photo-diode Dm and in the case where the detected light intensity is 
higher than the set light intensity, the signal is negatively fedback from 
the photo-diode Dm so that the potential at the connection B is higher 
than the value of the reference voltage Vcf applied to the connection C, 
as explained later. In this way the value of the voltage at the connection 
E descends so that the intensity of the emitted light is reduced. 
Similarly, in the case where the intensity of the emitted light is lower 
than the set intensity, the signal is negatively fedback from the 
photo-diode Dm so that the potential at the connection B is lower than the 
value of the reference voltage Vcf applied to the connection C. In this 
way the value of the voltage at the connection E rises so that the 
intensity of the emitted light is increased. Consequently the intensity of 
the light, with which the optical recording medium is irradiated, by the 
laser diode De is stabilized in a stationary state, depending on the value 
of the reference voltage Vcf applied to the connection C. 
In the photo-diode Dm, to which a bias voltage is applied in the backward 
direction, the impedance RIDm in the backward direction produced between 
the cathode and the anode inversely proportionally to the increase in the 
intensity of the light illuminating the photo-diode Dm decreases. Together 
with this decrease of the impedance RIDm, the monitor current Im flowing 
through the path of power source Vcc .fwdarw. from anode to cathode of the 
photo-diode Dm .fwdarw. resistance 3 .fwdarw. from collector to emitter of 
the transistor 4 .fwdarw. ground line GND increases. Supposing a case 
where the value of the base current Ib8 limited by the value of the 
resistance R1 (.OMEGA.) of the resistance 1 and flowing through the 
transistor 4 from the base to the emitter becomes constant in the state 
where the voltage measured at the two extremities of the capacitor. 2 is 
saturated, denoting the value of the power source voltage by Vcc (V), the 
internal resistance of the power source by Rcc (.OMEGA.), the impedance in 
the backward direction between the cathode and the anode of the 
photo-diode Dm by RIDm (.OMEGA.), the resistance value of the resistance 3 
by R3 (.OMEGA.), the value of the divided voltage given at this time 
between the collector and the emitter of the transistor 4 by Vce4 (V), and 
the internal resistance at this time between the collector and the emitter 
of the transistor 4 by Rce8 (.OMEGA.), the value of the monitor current Im 
(A) has a value of the negative feedback expressed by the following 
equation: 
EQU Im=(Vcc-Vce4)/(RIDm+R3+Rce8) 
Denoting the resistance value of the resistance 5 by R5 (.OMEGA.), the 
initiation judgment current Isd (A) flowing through the path of power 
source Vcc .fwdarw. resistance 5 .fwdarw. resistance 3 .fwdarw. from 
collector to emitter of the transistor 4 .fwdarw. ground line GND, in the 
state where the value of the base current Ib8 flowing through the 
transistor 4 between the base and the emitter limited by the value of the 
resistance R1 (.OMEGA.) of the resistance 1 is constant when the voltage 
between the two terminals of the capacitor 2 is saturated, has a value 
expressed by the following equation; 
EQU Isd=(Vcc-Vce4)/(R3+R5+Rce8) 
Consequently a resultant current Isd + Im of the initiation judgment 
current Isd and the monitor current Im flows through the path of 
resistance 3 .fwdarw. from collector to emitter of the transistor 4 
.fwdarw. ground line GND and controlled by a closed loop so as to approach 
the value of the reference voltage at the connection C, the potential VB 
(V) at the connection B in the stationary state has a value expressed by 
the following equation; 
EQU VB=(Isd+Im).multidot.(R3+R5+Rce8)+Vce4 
Next the protecting operation in the state where an excessive driving 
current IDe flows through the laser diode De will be explained. The 
driving current IDe is made flow through the path of power source Vcc 
.fwdarw. from anode to cathode of the laser diode De .fwdarw. from 
collector to emitter of the transistor 18 .fwdarw. resistance 19 .fwdarw. 
ground line GND. The state where the value of the driving current IDe is 
excessive takes place by the fact that e.g. when the instructing signal 
input VE from the control section 300 is applied at a high potential by 
some cause, an excessively high current is made flow through the laser 
diode De, which tends to destroy it. A current detection signal VR19 
produced at this time between the two terminals of the resistance 19 
corresponding to the value of the voltage to be compared Vin rises to a 
level exceeding the base-emitter voltage Vbe20 of the transistor 20 and 
thus a base current Ibe20 flows through the transistor 20 between the base 
and the emitter. In this way an excessive current detection value Ice20 
depending on the value of the base current Ibe20 flows through the path of 
power source Vcc .fwdarw. resistance 25 .fwdarw. from collector to emitter 
of the transistor 20 .fwdarw. ground line GND. At this time the potential 
at the connection F, through which the excessive current detection value 
Ice20 flows, becomes lower than the value of the reference voltage Vref 
applied to the inverting input-of the operational amplifier 11. 
Consequently the output terminal of the operational amplifier 11 is 
shifted to the "L" level and kept. Thus the protection instructing signal 
is applied to the connection E. Since the current intensity instructing 
signal applied from the control section 300 to the instructing signal 
input point De passes through the path of resistance 15 .fwdarw. from 
anode to cathode of the diode 13 .fwdarw. from output terminal of the 
operational amplifier 11 to negative power supplying terminal not shown in 
the figure .fwdarw. ground line GND, a state where the potential at the 
connection E is lowered is realized and further since no base current 
Ibe18 flows through the transistor 18, the driving current to the laser 
diode De in the state where the protection instructing signal is applied 
is interrupted and a protecting operation state where this driving current 
is cancelled is realized. At the same time as the state enters this 
protecting operation state, a positive feedback current flows through the 
path of power source Vcc .fwdarw. from anode to cathode of the diode 12 
.fwdarw. from output terminal of the operational amplifier 11 to negative 
power supplying terminal not shown in the figure .fwdarw. ground line GND. 
In the holding operation state where the positive feedback current flows 
through the common connecting point F of the collectors of the transistors 
20 and 26, the resistance 25, and the anode of the diode 12, even if the 
current detection signal VR19 becomes lower than the base-emitter voltage 
Vbe20 of the transistor 20, the potential applied to the non-inverting 
input terminal - of the operational amplifier 11 exceeds never the value 
of the reference voltage Vref. Furthermore, even if a voltage higher than 
the value of the reference voltage Vref is applied to the base of the 
transistors 19 and 26, this state is never transmitted to the collectors 
of the transistors 19 and 26, the holding operation continues to be 
maintained. 
Next the protecting operation in the state where the temperature approaches 
that of the destruction of the laser diode De will be explained. Even in 
the state where the driving current having an intensity lower than an 
excessive current flows through the laser diode De, the probability of the 
destruction of the laser diode De is high, if the temperature thereof 
rises. This temperature rise is transferred to the thermistor 22 and the 
value of the impedance of the thermistor 22 is lowered. The power source 
voltage Vcc is stabilized by a voltage stabilizing circuit consisting of 
the resistance 21, the Zener diode 23 and the capacitor 24 and an 
excessive current obtained by dividing the value of this stabilized 
voltage by the sum of the value of the impedance of the thermistor 22 and 
the resistance 26 flows through the thermistor 22. At this time a current 
intensity detecting signal produced between the two terminals of the 
resistance 26 corresponding to the value of the voltage to be compared Vin 
rises to a level higher than the base-emitter voltage Vbe27 of the 
transistor 27 and the base current Ibe27 flows through the transistor 27 
between the base and the emitter. An excessive current detection value 
depending on the value of the base current Ibe27 flows through the path of 
resistance 25 .fwdarw. from collector to emitter of the transistor 27 
.fwdarw. ground line GND in this state. The potential at the connection F, 
through which this excessive current detection value Ice20 flows, is lower 
than the value of the reference voltage Vref applied to the inverting 
input - of the operational amplifier 11. Consequently the output terminal 
of the operational amplifier 11 is shifted to the "L" level and held and 
the protection instructing signal is applied to the connection E. The 
driving current to the laser diode in the state where the protection 
instructing signal is applied is cancelled by the fact that the current 
intensity instructing signal applied from the control section 300 to the 
instructing signal input point E flows through the path of resistance 15 
.fwdarw. from anode to cathode of the diode 13 .fwdarw. from output 
terminal of the operational amplifier 11 to negative power source 
supplying terminal not shown in the figure .fwdarw. ground line GND. Since 
no base current Ibe18 flows through the transistor 18, the transistor 18 
is cut off and the protecting operation state is realized. Furthermore, in 
this state, a holding current flows through the path of power source Vcc 
.fwdarw. from anode to cathode of the diode 12 .fwdarw. from output 
terminal of the operational amplifier 11 to negative power source terminal 
not shown in the figure .fwdarw. ground line GND so that the potential at 
the connection F is approximately equal to the forward direction voltage 
value VFD12 allotted to the diode 12 between the anode and the cathode by 
the voltage division. Consequently, since it exceeds never the value of 
the reference voltage Vref applied to the inverting input terminal - of 
the operational amplifier 11, it is held similarly to the protecting 
operation by the excessive current. 
Next the reset operation to return the protecting operation by the 
excessive current and the excessive heat to the original state will be 
explained. A pulse signal of "H" level supplied from the reset instructing 
circuit not shown in the figure, e.g. by a manual operation, etc., is 
applied to the reset terminal. The collector-emitter circuit of the 
transistor 8 is made conductive by this pulse signal. Denoting the 
resistance value of the resistance 6 by R6 (.OMEGA.), the resistance value 
of the resistance 7 by R7 (.OMEGA.), and the value of the voltage allotted 
to the conductive transistor 8 between the collector and the emitter by 
the voltage division by Vce8 (V), the value of the reset voltage Vs (V) 
applied to the inverting input terminal of the operational amplifier 11, 
which voltage is equal to the potential at the connection G, is equal to 
the voltage value represented by the following equation; 
EQU Vs=Vcc-(R6+R7)(Vcc-Vce8)/(R6+R7) 
In the operational amplifier 11, to which this value of the reset voltage 
Vs (V) is once applied, at this time, since the value of the reset voltage 
Vs (V) becomes lower than the value of the forward voltage VFD12 applied 
to the non-inverting input terminal +, the output terminal is shifted to 
the "H" level and the holding state is reset. The potential Vcr (V) at the 
terminal C as far as the value of the reset voltage Vs (V) is applied to 
the operational amplifier 11 has a value, which is lower than the value of 
the reference voltage Vcf indicating the central value of the intensity of 
the light emitted by the laser diode De, and which is expressed by the 
following equation; 
EQU Vcr=Vce8+(Vcc-Vce8).multidot.R7/(R6+R7) 
An instructing signal for starting again the operation is supplied from the 
control section 300, to which the value of the reference voltage Vcr 
instructing this low intensity of the emitted light is applied, to the 
base of the transistor 18. When the reset terminal is returned to the "L" 
level, an instructing signal instructing the emission of the light in the 
stationary state is supplied from the control section 300. Consequently, 
in the new starting state, since an instructing signal to increase 
stepwise the intensity from the value of the reference voltage Vcr 
instructing a low intensity of the emitted light to the value of the 
reference voltage Vcr instructing a intensity of the emitted light in the 
stationary state, stress given to the laser diode De is small. Further, in 
the case where an improper state is detected again by the operation 
detecting section 200, if the driving function of the transistor 18 is 
normal, the interruption of the driving current IDe is effected in the 
state where the stress given to the laser diode De is small. 
Although the initiation detecting section 100 explained in the above 
embodiment is so constructed that the initiation instructing signal at the 
switch-on of the power source is obtained by integrating the applied power 
source voltage, this invention is not restricted thereto, but it can be 
modified to a digital circuit, which generates an initiation instructing 
signal for effecting a soft start operation predetermined on the basis 
that the power source has been switched on. Further, although both the 
initiation instructing signal from the initiation detecting section 100 
and the negative fedback value from the monitor diode Dm are supplied to 
the inverting input terminal - (connection B), which is the control 
terminal of the control section 300 explained in the above embodiment, it 
is a matter of course that the input terminal can be changed to the 
non-inverting input terminal + side of the control section 300, if the 
design is changed so that the polarity of the initiation instructing 
signal of the initiation detecting section 100 is inverted. 
Still further, even if the resistance 19 for detecting the value of the 
driving current IDe connected in series with the laser diode De is set to 
a relatively low resistance value with respect to the resistance 73 for 
limiting current used in the prior art example, since it is 
current-controlled by the transistor 18 on the basis of the negative 
feedback value of the monitor diode Dm, it can be operated without any 
special problem. 
Since the semiconductor laser driving circuit thus constructed is 
current-controlled by the transistor 18, it can be operated stably even 
with a relatively low value of the power source voltage Vcc and thus it is 
very convenient to apply it to hand held type apparatuses, which widens 
the field of the practical use thereof. 
Hereinbelow a third embodiment of this invention having the third technical 
means will be explained in detail, referring to FIGS. 8 to 10. 
FIGS. 9(a) to 9(f) are circuit diagram illustrating the construction of the 
circuit according to the present invention; FIGS. 10(a) to 10(d) are 
schemes showing waveforms for explaining the working mode of the circuit 
construction according to the present invention; and FIG. 8 is a circuit 
diagram of the semiconductor laser drive control device, to which the 
present invention is applied. 
In the figures reference numerals 1, 3, 5, 6, 7, 9, 14, 15, 19, 21, 25, 26, 
59, 61, 62 are resistances; 2, 16, 24 are capacitors; 4, 8, 18, 20, 27 are 
NPN type bipolar transistors; 10, 11, 51 are two-terminal-input type 
operational amplifiers; 12, 13, 57, 58 are diodes; 17 is a monitor diode 
incorporation type light emitting diode unit; 22 is a temperature 
detecting thermistor; 23 is a Zener diode; 53 is an input terminal; 54 is 
a reference voltage generating circuit; 55 is a reset terminal; 56 is an 
output terminal; 60 is a reset voltage generating circuit; De is a laser 
diode; Dm is a photo-diode; Sr is a reset switch; 100 is an initiation 
detecting section; 200 is an operation detecting section; 300 is a control 
section; and 400 is an operation voltage generating section. 
At first, the basic construction of the device according to the present 
invention will be explained, referring to FIGS. 9(a) and 9(b). 
The operational amplifier 51 indicated in FIG. 9(a) is so constructed that 
the negative power source terminal not indicated in the figures is 
connected with the ground line, while the positive power source terminal 
not indicated in the figures is connected with the positive pole of the 
power source Vcc so as to effect a comparing operation. The cathode of the 
diode 57 serving as positive feedback means is connected with the 
non-inverting input +, which is the comparing input terminal of this 
operational amplifier 51 and the anode thereof is connected with the 
output terminal 56 of the operational amplifier 51 so that the positive 
feedback current is supplied from the output terminal 56 to the 
non-inverting input terminal +. 
The cathode of the diode 58, which is voltage dividing means, is connected 
with the common connection between this non-inverting input + and the 
cathode of the diode 57 and this cathode is connected with the input 
terminal 53, to which the input signal Vin, which is the voltage to be 
compared, is supplied so that the signal current is supplied from the 
input terminal 53 to the non-inverting input terminal +. 
On the other hand the common terminal of the reset switch is connected with 
the inverting input terminal - serving as the reference input terminal of 
the operational amplifier 51 and the reference voltage generating circuit 
54 and the reset voltage generating circuit 60 are connected with the 
first and the second switching terminal of this reset switch Sr, 
respectively. This reset switch Sr is so constructed that depending on the 
reset instruction applied to the reset terminal 55, it is turned on from 
the comparing operation state where the reference voltage Vref from the 
reference voltage generating circuit 54 is applied to the inverting input 
terminal - to the returning operation state from the holding operation 
where the reset voltage Vs from the reset voltage generating circuit 60 is 
applied to the inverting input terminal -. In such a structure, in which 
the output signal Vout at the output terminal 56 is inverted when the 
input signal Vin is great with respect to the reference voltage Vref, the 
reset voltage is set so as to be higher than the reference voltage Vref. 
In the construction indicated in FIG. 9(b), only the diode 57, which is 
positive feedback means in the construction indicated in FIG. 9(a), is 
replaced by the resistance 59. 
In the construction indicated in FIG. 9(c), only the diode 57, which is 
voltage dividing means in the construction indicated in FIG. 9(a), is 
replaced by the resistance 61. 
In the construction where the output signal Vout at the output terminal 56 
is inverted when the input signal Vin is smaller than the reference 
voltage Vref, the reset voltage is set so as to be lower than the 
reference voltage Vref, as indicated in FIGS. 9(d), 9(e) and 9(f). These 
circuits are so constructed that FIG. 9(d) corresponds to FIG. 9(a); FIG. 
9(b) corresponds to FIG. 9(e); and FIG. 9(c) corresponds to FIG. 9(f). A 
pull up voltage is always applied from the positive pole of the power 
source Vcc through the resistance 62 to the non-inverting input terminal 
+. 
Now the operation will be explained, referring to FIGS. 10(a) and 10(b). 
When the input signal Vin indicated by a full line in FIG. 10(a) is applied 
to the input terminal 53, a substraction value Vin - VDF58 obtained by 
substracting the voltage VDF58 in the forward direction across the diode 
58 from the input signal Vin, which is indicated in the chain-dotted line 
in FIG. 10(a), exceeds the reference voltage Vref indicated by the broken 
line in FIG. 10(a) at a point of time t1 in FIG. 10(a) and thus the output 
signal Vout indicated in FIG. 10(b) is changed to the "H" level. The 
output signal Vout changed to the "H" level exceeds the voltage VDF57 in 
the forward direction across the diode 57 and thus the positive feedback 
current flows therethrough. In this way the state where the output signal 
Vout is changed to the "H" level. This state of the output signal Vout is 
stably maintained, because the value of the voltage Vin - VDF58 applied to 
the non-inverting input terminal + exceeds never the voltage in the 
backward direction of the diode 58 owing to the positive feedback current, 
which is made flow therethrough, and the input impedance of the 
non-inverting input terminal + is set so as to be extremely high. The 
holding operation maintained by this value of the voltage Vin - VDF57 is 
continued to be held, even if the substraction value Vin - VDF58 becomes 
lower than the reference voltage Vref at the point of time t2 in FIG. 
10(a), because no current flows through the diode in the backward 
direction. 
When a pulse reset signal RS of "H" level indicated in FIG. 10(b) is 
supplied, a value of the reset voltage Vs outputted by the reset signal 
generating circuit 60, which is indicated by a two-dot-one-dash line in 
FIG. 10(a) and which is higher than the reference voltage Vref, is applied 
for a short time to the inverting input terminal - through the reset 
switch. As the result, the output signal Vout indicated in FIG. 10(b) is 
changed to the "L" level and the holding state is removed. After the 
termination of this removing operation of short time, the comparing 
operation is effected in the state where the output signal Vout is at the 
"L" level, until the subtraction value Vin - VDF58 exceeds the reference 
voltage Vref at the next time. 
In the circuit construction indicated in FIG. 9(b), current through the 
resistance 59, which is set to a relatively high impedance value on the 
basis of the difference between the substraction value Vin - VDF58 and the 
output signal Vout at the "L" level, is made flow to the output terminal 
56. However, almost all the subtraction value Vin - VDF58 applied to the 
non-inverting input terminal + is divided by the resistance 59 and a 
value, which is very close to the "L" level at the output terminal 56 is 
applied to an input terminal of a load, whose input impedance value is set 
so as to be high with respect to the output impedance value of the output 
terminal 56 at the "L" level state, connected with the output terminal 56. 
Then the positive feedback current If is made flow through the resistance 
59 on the basis of the output signal Vout at the "H" level state and the 
procedure proceeds to the holding operation. A subtraction value Vout - 
R59.multidot.If obtained by subtracting the voltage drop across the 
resistance 59, through which the feedback current If flows, from the 
output voltage Vout is applied to the non-inverting input terminal + in 
this case. This applied voltage approaches a value, which is approximately 
equal to the output voltage Vout, in a relatively short time. Since in 
this holding operation no discharge takes place through the diode 58, the 
holding operation is maintained similarly to the case by the circuit 
construction indicated in FIG. 9(a). 
In the circuit construction indicated in FIG. 9(c), a subtraction value Vin 
- R61.multidot.Ii obtained by subtracting from the input signal Vi a value 
R61.multidot.Ii obtained by the voltage division due to an extremely short 
and weak input current Ii responding to variations in the input signal Vin 
applied to the resistance 61, whose impedance is set to a relatively high 
value. When an extremely short predetermined period of time measured from 
the point of time, where variations in the input signal Vin disappeared, 
has lapsed, a voltage value having the same level as the input signal Vin 
applied to the input terminal 58 is applied to the non-inverting input +. 
These voltages applied to the non-inverting input + are obstructed by the 
diode 57 and never applied to the load connected with the output terminal 
56. As the result, no erroneous operations take place, even if a load, 
whose input impedance value is relatively low with a low driving voltage 
with respect to the maximum value of the input signal Vin, is connected 
with the output terminal 56. 
When the value of the voltage applied to the non-inverting input + exceeds 
the reference voltage Vref, the output signal Vout is changed to the "H" 
level and the positive feedback current is made flow through the diode 57. 
Thus the procedure enters the holding operation. Since the value of the 
series impedance R61 + Rin of the output impedance of the signal supplying 
circuit connected with the input terminal 53 and the resistance 61 is very 
high, the value (Vout - VDF57 - Vin)/(R61 + Rin) of the current made flow 
through the resistance 61 by the potential difference Vout - VDF57 - Vin 
between the value of the voltage Vout - VDF57 applied to the non-inverting 
terminal + and the input voltage Vin at the input terminal 53 is very 
small. Therefore a voltage value (R61 + Rin).multidot.(Vout - VDF57 - 
Vin)/(R61 + Rin), which is slightly lower than the voltage value Vout - 
VDF57, is applied to the non-inverting input + and the holding operation 
is continued to be maintained. 
In the circuit construction indicated in FIG. 9(d), the positive pole power 
source voltage Vcc is applied always to the non-inverting input terminal + 
serving as the comparison input terminal through the resistance 62. The 
power source voltage Vcc is continued to be applied to the non-inverting 
terminal +, until at least one of the signal current Is of the signal 
source from the diode 58, which is voltage dividing means, and the 
positive feedback current If from the diode 57, which is positive feedback 
means, towards the output terminal 56 of the operational amplifier 51 is 
made flow to the common ground line GND, which is the negative pole of the 
power source. In this state, since the value of the power source voltage 
Vcc applied to the non-inverting input terminal + becomes never lower than 
the reference voltage Vref of the reference voltage generating circuit 54 
applied to the inverting input terminal - serving as the reference input 
terminal, the output signal Vout of "H" level, which is approximately 
equal to the voltage value Vcc at the positive pole of the power source, 
is continued to be outputted from the output terminal 56 of the 
operational amplifier 51. 
Then the voltage value of the input signal Vin applied to the input 
terminal 53 decreases gradually and when it becomes lower than the 
substraction value Vcc - VDF58 obtained by substracting the forward 
direction voltage VDF58 across the diode 58 from the voltage value of the 
power source Vcc, the signal current Is is made flow through the path of 
power source voltage Vcc at the positive pole .fwdarw. resistance 62 
.fwdarw. diode 58 .fwdarw. signal source .fwdarw. ground line GND in this 
order. In the state where the value of the voltage drop Is.multidot.R62 
produced across the resistance 62 by the value of this signal current Is 
exceeds the substraction value Vref - VDF58 obtained by subtracting the 
forward direction voltage VDF58 from the reference voltage Vref, since the 
addition value Vin + VDF58 obtained by adding the forward direction 
voltage VDF58 of the diode 58 to the input signal Vin applied to the 
non-inverting input terminal + becomes lower than the reference voltage 
Vref at the inverting input terminal -, the output signal Vout of "L" 
level, which is approximately equal to the GND level at the negative pole 
of the power source, is outputted through the output terminal 56 of the 
operational amplifier 56. By the output signal Vout at the output terminal 
56 in this state, the positive feedback current If is made flow through 
the path of resistance 62 .fwdarw. diode 57 .fwdarw. output terminal 56 
.fwdarw. ground line GND. As the result, even if the input signal Vin 
rises and the signal current Is is interrupted, the subtraction value Vcc 
- If.multidot.R62 - VDF57 obtained by subtracting the value of the voltage 
drop If.multidot.R62 produced across the resistance 62 by the positive 
feedback current If and the forward direction voltage VDF57 across the 
diode 57 from the value of the power source voltage Vcc applied to the 
non-inverting input terminal + exceeds never the reference voltage Vref, 
the "L" level output state is continued to be maintained. 
In the state where the addition value Vin + VDF58 obtained by adding the 
forward direction voltage VDF57 across the diode 57 to the input signal 
Vin exceeds the reference voltage Vref, by the fact that the reset signal 
RS is supplied to the reset switch Sr, the reset voltage Vs from the reset 
voltage generating circuit 60, which becomes lower than the subtraction 
value Vcc - If.multidot.R62 - VDF57, is applied to the inverting input 
terminal - and thus the output signal Vout held at the "L" level returns 
to the "H" level. 
In the circuit construction indicated in FIG. 9(e), when the output signal 
Vout is changed to the "L" level, the potential at the non-inverting input 
terminal + is moved to a potential, which is approximately equal to the 
"L" level, through the resistance 59 serving as the positive feedback 
means and the state where the input signal Vin doesn't exceed the backward 
direction voltage VDR 58 of the diode 62 is maintained. 
In the circuit construction indicated in FIG. 9(f), a decreased input 
signal Vin is applied through the resistance 61; the potential at the 
non-inverting input terminal + becomes lower than the reference voltage 
Vref; and thus the output signal Vout is moved to the "L" level and 
maintained. Even if the reset voltage Vs is applied to the inverting input 
terminal - and the output voltage Vout is changed to the "H" level, since 
the output signal Vout of "H" level never exceeds the backward direction 
voltage VDR57 of the diode 57, the output voltage Vout continues to 
return. 
Further, if the diodes 57 and 58 described above are replaced by a 
construction rectifying the flow of signals by means of transistors, 
buffer amplifiers, etc., the device can be operated in the same way. 
Hereinbelow and embodiment, in which a comparator with latch according to 
the present invention is applied to a semiconductor laser driving control 
device used for an optical reading device, etc., will be explained in 
detail, referring to FIG. 8. 
At first, the construction of the device will be explained. In the light 
emitting diode unit 17 there are disposed the laser diode De for 
irradiating the optical recording medium with a laser light beam and the 
PIN type photo-diode Dm for monitoring the intensity of the light emission 
of this laser diode De. It is so constructed that the cathode of the 
photo-diode Dm is connected with the anode of the laser diode De. The 
power source voltage Vcc is applied to the connection of the anode of the 
laser diode De with the cathode of the photo-diode Dm. The anode of the 
photo-diode Dm is connected with the comparision input point B for 
effecting the control of the intensity of the light emission of the laser 
diode De disposed in the control section 300 explained later. The cathode 
of this laser diode De is connected with the collector of the driving NPN 
type transistor 18 for controlling the current flowing through the laser 
diode De. The emitter of this transistor 18 is grounded through the 
resistance 19 for detecting the intensity of the conduction current of the 
operation detecting section 200 explained later. The base of this 
transistor 18 is constructed as an instruction signal input point E, to 
which a protection instruction and conduction current intensity 
instruction outputted by both the operation detecting section 200 
described later and the control section 300. On the other hand the laser 
diode De is so constructed that heat produced by the laser diode De, 
through which current flows, is transferred to the thermistor 22 for 
detecting the temperature. The power source voltage Vcc is applied through 
the resistance 21 to an end of this thermistor 22. The connection of this 
thermistor 22 with the resistance 21 is grounded through the Zener diode 
23, whose cathode is connected therewith for generating a constant 
voltage, and the capacitor similarly for bypassing alternating current 
component, which are connected in parallel. The other end of the 
thermistor 22 is grounded through the resistance 26 disposed on the 
operation detection section 200 described later for detecting the 
intensity of the current flowing therethrough, which increases with 
increasing temperature of the thermistor 22. 
In the initiation detecting section 100 the resistance 1 and the capacitor 
2 are connected in series between the power source terminal Vcc, with 
which the positive pole of the power source voltage Vcc is connected, and 
the common ground line GND, with which the negative pole of the power 
source voltage Vcc is connected. The base of the NPN type transistor 4 is 
connected with the common connecting point A between this resistance 1 and 
the capacitor 2. The emitter of this transistor 4 is grounded and the 
collector thereof is connected with an end of the resistance 3. The power 
source voltage Vcc is applied to the other end of this resistance 3 
through the resistance 5 set to a value extremely high with respect to the 
value of the resistance 3. The connection between the resistances 5 and 3 
constitutes the output terminal of the initiation detecting section 100. 
These are constructed so as to output an initiation judging signal, which 
decreases relatively slowly, for preventing the destruction accident of 
the laser diode De at the switching on of the power source Vcc, by the 
fact that the value of the voltage applied to the comparison input point B 
in the control section 300 described later is raised to the value of a 
voltage, which is extremely close to the power source voltage Vcc, only 
during a period of time determined depending on the time constant of the 
resistance 1 and the capacitor 2, starting from the point of time where 
the power source voltage Vcc is turned on. 
The bases of the NPN type transistors are connected with the connection of 
the resistance 19 in the operation detection section 200 with the emitter 
of the transistor 18 and the connection of the resistance 26 with the 
thermistor 22, respectively. The power source voltage Vcc is applied to 
the collectors of these transistors 20 and 27 through the resistance 25 
for pull-up and both the emitters thereof are grounded. This circuit is so 
constructed that the connection F of the collectors of these transistors 
20 and 27 with the resistance F supplies an anormality detection signal to 
the non-inverting input terminal + of the operational amplifier 11, which 
anormality detection signal is of "L" level, when an excessively high 
intensity of the current increasing with excessive increase of the current 
flowing through the laser diode De and with temperature rise of the 
thermistor 22 is found. The operational amplifier 11, to which the 
anormality detection signal of "L" level is supplied, is constructed so as 
to act as a comparator with latch holding the output state of "L" level, 
until it is reset. The anode and the cathode of the diode 12, through 
which the positive feedback current flows, are connected with the 
non-inverting input terminal + and output terminal of this operational 
amplifier 11, respectively. The value of the reference voltage Vref 
indicating the threshold value, which is the limit of the normal operation 
of the laser diode De, from the operation voltage generating section 400 
described later and the value of the reset voltage Vs from the transistor 
8 stated later are supplied to the inverting input terminal - of this 
operational amplifier 11. The cathode of the diode 13 preventing to 
transmit the "H" level of this output terminal to the instructing signal 
input point E is connected with the output terminal of this operational 
amplifier 11. The anode thereof is connected with one end of the 
resistance 15 limiting the intensity of the current flowing therethrough, 
when the output terminal of the operational amplifier is at the "L" level, 
and the other end is connected with the instructing signal input point E, 
which is the base of the transistor 18. The circuit is so constructed that 
the current flowing through a series circuit consisting of this resistance 
15 and the diode 13 serves as the protection instructing signal for 
cancelling the current intensity instructing signal applied from the 
control section 300 to the instructing signal input point E, owing to the 
fact that the value of the voltage to be compared Vin corresponding to the 
voltage drop across the resistances 20 and 27 serving as a signal source 
exceeds the value of the voltage Vbe, at which the current begins to flow 
in the forward direction between the base and the emitter of the 
transistors 20 and 27, and at this time the value of the voltage at the 
connection F between the transistors 20 and 27 having the rectifying and 
the voltage dividing function and effecting the detection operation 
becomes once lower than the value of reference voltage Vref applied to the 
operational amplifier 11 so that the output terminal of the operational 
amplifier 11 is held at the "L" level, only until the value of the reset 
voltage Vs is applied to the inverting input terminal - of the operational 
amplifier 11. 
The operational amplifier 10 in the control section 300 is constructed so 
as to work as a comparator, which outputs the "H" level, when the value of 
the voltage applied to the comparison input point B of the control section 
300, where the initiation detecting signal is applied to the inverting 
terminal - of the operational amplifier 10, connected with the anode of 
the photo-diode Dm as well as the resistances 3 and 5 exceeds the value of 
the reference voltage applied from the operation voltage generating 
section 400 stated later to the non-inverting input terminal + of this 
operational amplifier 10, and the "L" level, when the former becomes lower 
than the latter. The output terminal of the operational amplifier 10 is 
grounded through the resistance 14 and the capacitor 16. The connection E 
of the resistance 14 with the capacitor 16 in the control section 300 is 
connected with the base of the transistor 18 driving the laser diode De. 
The series circuit consisting of the resistance 14 and the capacitor 16 is 
constructed as an integrating circuit outputting a value of a DC voltage 
proportional to the ratio in time, with which the output terminal of the 
operational amplifier 10 outputs the "H" level. 
In the operation voltage generating means 400 a series circuit consisting 
of the resistance 6, the resistance 8 and the resistance 8 is connected 
between the voltage source Vcc and the ground line GND. It is so 
constructed that the value of the voltage indicating the intensity of the 
light emitted by the laser diode De is supplied from the connection C 
between the resistance 6 and the resistance 7 to the non-inverting input 
terminal + of the operational amplifier 11 and that the value of the 
voltage indicating the holding and releasing operation is supplied from 
the connection G between the resistance 7 and the resistance 8 to the 
inverting input terminal - of the operational amplifier 11. The collector 
of the transistor 8 for the reset is also connected with this connection 
G. The emitter of this transistor 8 is grounded. As far as a reset signal 
of "H" level is applied to the base of the transistor 8, the collector and 
the emitter of the transistor 8 are in the low impedance state. As far as 
a reset signal of "L" level is applied to the base of the transistor 8, 
the value of the reference voltage Vcf indicating the center value of the 
intensity of the light emitted by the laser diode De is outputted from the 
connection C and the value of the reference voltage Vref indicating the 
threshold value of the holding operation of the operational amplifier 11 
is outputted from the connection D. As far as a reset signal of "H" level 
is applied to the base of the transistor 8, a value of the voltage Vcr 
indicating an intensity of the light emission lower than the central value 
of the intensity of the light emitted by the laser diode De is outputted 
from the connection C and a value of the reset voltage Vs indicating the 
releasing operation of the holding state of the operational amplifier 11 
is outputted from the connection G. 
Hereinbelow the operation of the construction described above, referring to 
FIG. 8, will be explained. 
At first, when the power source of the code reading device is switched on, 
the potential at the non-inverting input terminal + (connection C) of the 
operational amplifier 10 arrives at the same time as the switch-on of the 
power source Vcc at the value of the reference voltage Vcf indicating the 
central value of the intensity of the light emitted by the laser diode De, 
expressed by the following equation; 
EQU Vcf=Vcc.multidot.(R7+R9)/(R6+R7+R9) 
On the contrary, the potential at the inverting input terminal - 
(connection B) of the operational amplifier 10 rises according to 
predetermined characteristics together with the potential of the 
connection A, which rises with a certain time constant determined by the 
time constant circuit consisting of the resistance 1 and the capacitor 2 
and an initiation judging current Isd flows through the path of power 
source Vcc .fwdarw. resistance 5 .fwdarw. resistance 3 .fwdarw. from 
collector to emitter of the transistor 4 .fwdarw. ground line GND with the 
rising potential at the connection A. This initiation judging current Isd 
charges the capacitor 2 and increases relatively slowly, corresponding to 
the base current Ibe4, which is made flow by the fact that th voltage Veb4 
applied between the base and the emitter of the transistor 4 arrives at a 
predetermined value (e.g. + 0.06 V), until it is saturated, depending on 
the resistance 1 and the current amplification factor h.sub.fe of the 
transistor 4. The potential at the connection B, which rises according to 
the increasing characteristics of the intensity of this base current Ice4 
descends to a potential, obtained by dividing the power source voltage by 
the resistance 5 set to a relatively high resistance value on one side and 
the resistance 3 set to a relatively low resistance value and the circuit 
between the collector and the emitter of the transistor 4 on the other 
side, which is somewhat lower than the value of the reference voltage Vcf 
at the connection C. Corresponding thereto, the potential at the 
connection E rises to a value of the voltage, with which a value of the 
driving current giving rise to an intensity of light somewhat higher than 
the central value of the light intensity emitted by the laser diode De by 
the fact that the ratio in time, with which the "H" level signal is 
outputted from the output terminal of the operational amplifier 10, 
increases gradually. Consequently the intensity of the driving current 
flowing through the laser diode De rises not rapidly at the switch-on of 
the power source and thus a so-called soft start is effected so that the 
intensity of the emitted light rises with an appropriate speed, until an 
intensity of emitted light arrives at a predetermined value. 
The intensity of the light emitted by the laser diode De is detected by the 
photo-diode Dm and in the case where the detected light intensity is 
higher than the set light intensity, the signal is negatively fedback from 
the photo-diode Dm so that the potential at the connection B is higher 
than the value of the reference voltage Vcf applied to the connection C, 
as explained later. In this way the value of the voltage at the connection 
E descends so that the intensity of the emitted light is reduced. 
Similarly, in the case where the intensity of the emitted light is lower 
than the set intensity, the signal is negatively fedback from the 
photo-diode Dm so that the potential at the connection B is lower than the 
value of the reference voltage Vcf applied to the connection C. In this 
way the value of the voltage at the connection E rises so that the 
intensity of the emitted light is increased. Consequently the intensity of 
the light, with which the optical recording medium is irradiated, by the 
laser diode De is stabilized in a stationary state, depending on the value 
of the reference voltage Vcf applied to the connection C. 
In the photo-diode Dm, to which a bias voltage is applied in the backward 
direction, the impedance RIDm in the backward direction produced between 
the cathode and the anode inversely proportionally to the increase in the 
intensity of the light illuminating the photo-diode Dm decreases. Together 
with this decrease of the impedance RIDm, the monitor current Im flowing 
through the path of power source Vcc .fwdarw. from anode to cathode of the 
photo-diode Dm .fwdarw. resistance 3 .fwdarw. from collector to emitter of 
the transistor 4 .fwdarw. ground line GND increases. Supposing a case 
where the value of the base current Ib8 limited by the value of the 
resistance R1 (.OMEGA.) of the resistance 1 and flowing through the 
transistor 4 from the base to the emitter becomes constant in the state 
where the voltage measured at the two extremities of the capacitor 2 is 
saturated, denoting the value of the power source voltage by Vcc (V), the 
internal resistance of the power source by Rcc (.OMEGA.), the impedance in 
the backward direction between the cathode and the anode of the 
photo-diode Dm by RIDm (.OMEGA.), the resistance value of the resistance 3 
by R3 (.OMEGA.), the value of the divided voltage given at this time 
between the collector and the emitter of the transistor 4 by Vce4 (V), and 
the internal resistance at this time between the collector and the emitter 
of the transistor 4 by Rce8 (.OMEGA.), the value of the monitor current Im 
(A) has a value of the negative feedback expressed by the following 
equation; 
EQU Im=(Vcc-Vce4)/(RIDm+R3+Rce8) 
Denoting the resistance value of the resistance 5 by R5 (.OMEGA.), the 
initiation judgment current Isd (A) flowing through the path of power 
source Vcc .fwdarw. resistance 5 .fwdarw. resistance 3 .fwdarw. from 
collector to emitter of the transistor 4 .fwdarw. ground line GND, in the 
state where the value of the base current Ib8 flowing through the 
transistor 4 between the base and the emitter limited by the value of the 
resistance R1 (.OMEGA.) of the resistance 1 is constant when the voltage 
between the two terminals of the capacitor 2 is saturated, has a value 
expressed by the following equation; 
EQU Isd=(Vcc-Vce4)/(R3+R5+Rce8) 
Consequently a resultant current Isd + Im of the initiation judgment 
current Isd and the monitor current Im flows through the path of 
resistance 3 .fwdarw. from collector to emitter of the transistor 4 
.fwdarw. ground line GND and controlled by a closed loop so as to approach 
the value of the reference voltage at the connection C, the potential VB 
(V) at the connection B in the stationary state has a value expressed by 
the following equation; 
EQU VB=(Isd+Im).multidot.(R3+R5+Rce8)+Vce4 
Next the protecting operation in the state where an excessive driving 
current IDe flows through the laser diode De will be explained. The 
driving current IDe is made flow through the path of power source Vcc 
.fwdarw. from anode to cathode of the laser diode De .fwdarw. from 
collector to emitter of the transistor 18 .fwdarw. resistance 19 .fwdarw. 
ground line GND. The state where the value of the driving current IDe is 
excessive takes place by the fact that e.g. when the instructing signal 
input VE from the control section 300 is applied at a high potential by 
some cause, an excessively high current is made flow through the laser 
diode De, which tends to destroy it. A current detection signal VR19 
produced at this time between the two terminals of the resistance 19 
corresponding to the value of the voltage to be compared Vin rises to a 
level exceeding the base-emitter voltage Vbe20 of the transistor 20 and 
thus a base current Ibe20 flows through the transistor 20 between the base 
and the emitter. In this way an excessive current detection value Ice20 
depending on the value of the base current Ibe20 flows through the path of 
power source Vcc .fwdarw. resistance 25 .fwdarw. from collector to emitter 
of the transistor 20 .fwdarw. ground line GND. At this time the potential 
at the connection F, through which the excessive current detection value 
Ice20 flows, becomes lower than the value of the reference voltage Vref 
applied to the inverting input - of the operational amplifier 11. 
Consequently the output terminal of the operational amplifier 11 is 
shifted to the "L" level and kept. Thus the protection instructing signal 
is applied to the connection E. Since the current intensity instructing 
signal applied from the control section 300 to the instructing signal 
input point De passes through the path of resistance 15 .fwdarw. from 
anode to cathode of the diode 13 .fwdarw. from output terminal of the 
operational amplifier 11 to negative power supplying terminal not shown in 
the figure .fwdarw. ground line GND, a state where the potential at the 
connection E is lowered is realized and further since no base current 
Ibe18 flows through the transistor 18, the driving current to the laser 
diode De in the state where the protection instructing signal is applied 
is interrupted and a protecting operation state where this driving current 
is cancelled is realized. At the same time as the state enters this 
protecting operation state, a positive feedback current flows through the 
path of power source Vcc .fwdarw. from anode to cathode of the diode 12 
.fwdarw. from output terminal of the operational amplifier 11 to negative 
power supplying terminal not shown in the figure .fwdarw. ground line GND. 
In the holding operation state where the positive feedback current flows 
through the common connecting point F of the collectors of the transistors 
20 and 26, the resistance 25, and the anode of the diode 12, even if the 
current detection signal VR19 becomes lower than the base - emitter 
voltage Vbe20 of the transistor 20, the potential applied to the 
non-inverting input terminal - of the operational amplifier 11 exceeds 
never the value of the reference voltage Vref. Furthermore, even if a 
voltage higher than the value of the reference voltage Vref is applied to 
the base of the transistors 19 and 26, this state is never transmitted to 
the collectors of the transistors 19 and 26, the holding operation 
continues to be maintained. 
Next the protecting operation in the state where the temperature approaches 
that of the destruction of the laser diode De will be explained. Even in 
the state where the driving current having an intensity lower than an 
excessive current flows through the laser diode De, the probability of the 
destruction of the laser diode De is high, if the temperature thereof 
rises. This temperature rise is transferred to the thermistor 22 and the 
value of the impedance of the thermistor 22 is lowered. The power source 
voltage Vcc is stabilized by a voltage stabilizing circuit consisting of 
the resistance 21, the Zener diode 23 and the capacitor 24 and an 
excessive current obtained by dividing the value of this stabilized 
voltage by the sum of the value of the impedance of the thermistor 22 and 
the resistance 26 flows through the thermistor 22. At this time a current 
intensity detecting signal produced between the two terminals of the 
resistance 26 corresponding to the value of the voltage to be compared Vin 
rises to a level higher than the base - emitter voltage Vbe27 of the 
transistor 27 and the base current Ibe27 flows through the transistor 27 
between the base and the emitter. An excessive current detection value 
depending on the value of the base current Ibe27 flows through the path of 
resistance 25 .fwdarw. from collector to emitter of the transistor 27 
.fwdarw. ground line GND in this state. The potential at the connection F, 
through which this excessive current detection value Ice20 flows, is lower 
than the value of the reference voltage Vref applied to the inverting 
input - of the operational amplifier 11. Consequently the output terminal 
of the operational amplifier 11 is shifted to the "L" level and held and 
the protection instructing signal is applied to the connection E. The 
driving current to the laser diode in the state where the protection 
instructing signal is applied is cancelled by the fact that the current 
intensity instructing signal applied from the control section 300 to the 
instructing signal input point E flows through the path of resistance 15 
.fwdarw. from anode to cathode of the diode 13 .fwdarw. from output 
terminal of the operational amplifier 11 to negative power source 
supplying terminal not shown in the figure .fwdarw. ground line GND. Since 
no base current Ibe18 flows through the transistor 18, the transistor 18 
is cut off and the protecting operation state is realized. Furthermore, in 
this state, a holding current flows through the path of power source Vcc 
.fwdarw. from anode to cathode of the diode 12 .fwdarw. from output 
terminal of the operational amplifier 11 to negative power source terminal 
not shown in the figure .fwdarw. ground line GND so that the potential at 
the connection F is approximately equal to the forward direction voltage 
value VFD12 allotted to the diode 12 between the anode and the cathode by 
the voltage division. Consequently, since it exceeds never the value of 
the reference voltage Vref applied to the inverting input terminal - of 
the operational amplifier 11, it is held similarly to the protecting 
operation by the excessive current. 
Next the reset operation to return the protecting operation by the 
excessive current and the excessive heat to the original state will be 
explained. A pulse signal of "H" level supplied from the reset instructing 
circuit not shown in the figure, e.g. by a manual operation, etc., is 
applied to the reset terminal. The collector - emitter circuit of the 
transistor 8 is made conductive by this pulse signal. Denoting the 
resistance value of the resistance 6 by R6 (.OMEGA.), the resistance value 
of the resistance 7 by R7 (.OMEGA.), and the value of the voltage allotted 
to the conductive transistor 8 between the collector and the emitter by 
the voltage division by Vce8 (V), the value of the reset voltage Vs (V) 
applied to the inverting input terminal of the operational amplifier 11, 
which voltage is equal to the potential at the connection G, is equal to 
the voltage value represented by the following equation; 
EQU Vs=Vcc-(R6+R7)(Vcc-Vce8)/(R6+R7) 
In the operational amplifier 11, to which this value of the reset voltage 
Vs (V) is once applied, at this time, since the value of the reset voltage 
Vs (V) becomes lower than the value of the forward voltage VFD12 applied 
to the non-inverting input terminal +, the output terminal is shifted to 
the "H" level and the holding state is reset. The potential Vcr (V) at the 
terminal C as far as the value of the reset voltage Vs (V) is applied to 
the operational amplifier 11 has a value, which is lower than the value of 
the reference voltage Vcf indicating the central value of the intensity of 
the light emitted by the laser diode De, and which is expressed by the 
following equation; 
EQU Vcr=Vce8+(Vcc-Vce8).multidot.R7/(R6+R7) 
An instructing signal for starting again the operation is supplied from the 
control section 300, to which the value of the reference voltage Vcr 
instructing this low intensity of the emitted light is applied, to the 
base of the transistor 18. When the reset terminal is returned to the "L" 
level, an instructing signal instructing the emission of the light in the 
stationary state is supplied from the control section 300. Consequently, 
in the new starting state, since an instructing signal to increase 
stepwise the intensity from the value of the reference voltage Vcr 
instructing a low intensity of the emitted light to the value of the 
reference voltage Vcr instructing a intensity of the emitted light in the 
stationary state, stress given to the laser diode De is small. Further, in 
the case where an improper state is detected again by the operation 
detecting section 200, if the driving function of the transistor 18 is 
normal, the interruption of the driving current IDe is effected in the 
state where the stress given to the laser diode De is small. 
Although in the present embodiment the present invention has been explained 
by using a construction using bipolar type transistors 19, 26 effecting 
the amplifying operation, setting the amount allotted to the dividing 
means having the rectifying function to "0", the present invention is not 
restricted thereto. Design modifications such as the amplifying operation 
using operational amplifiers, the comparing operation, the ideal diode 
operation, etc. may be carried out and further the amount allotted by the 
voltage division may be modified at need. Still further the positive 
feedback means can be modified, similarly to the voltage dividing means. 
Hereinbelow a fourth embodiment of the present invention having the fourth 
technical means will be explained in detail, referring to FIGS. 11 to 13. 
Hereinbelow an embodiment of the present invention will be explained in 
detail, referring to FIGS. 11 to 13. 
FIG. 11 is a block diagram showing the construction of a whole bar code 
scanner, which is a code reading device according to the present 
invention; FIG. 12 is a block diagram showing the construction of the 
principal part of the control structure of the device indicated in FIG. 
11; and FIG. 13 is a circuit diagram indicating the structure for 
processing the light reception signal. 
In the figures, reference numeral 1 is a control circuit; 2 is a light 
emission control section; 3 is a light emission driving circuit; 4 is a 
deflection control section; 5 is a deflection driving circuit; 6 is a 
focus adjusting control section; 7 is a focus adjusting drive circuit; 8 
is a preamplifier; 9 is an amplifying circuit; 10 is a binary coding 
circuit; 11 is a decode section; 12 is a light emitting element; 13 is a 
focus adjusting device; 14 is a focus adjusting lens; 15 is a holed 
mirror; 16 is a light receiving element; 17 is a fixed lens; 18 is a 
reflecting mirror; 19 is a galvano scanner; 20 is a bar code representing 
surface; 21 is an operation switch; 22 is a photo-electric converting 
section composed of the light emission driving circuit 3, the light 
emitting element 12, a light receiving element 16 and a preamplifier 8; 
30, 31, 32, 33, 34, 81, 82, 83, 84, 96 are operational amplifiers; 90 is 
an amplifying section; 91 is a reference voltage generating section; 92 is 
a feedback quantity setting section; 93 is a selecting section; 94 is a 
counter; 95 is a constant voltage power source section; 101 is an off 
signal generating circuit; 102 is a scanning counter; 103 is a constant 
memory; 104 is a comparing circuit; 111 is a decode circuit; 112 is an 
output circuit; C1 to C8 are capacitors; D1 to D4 are diodes; VR is a 
constant voltage power source element, Q1 is a PNP type transistor; R1 to 
R21 are resistances; Sc0 to Sc3 are switches and Vcc is a positive pole 
terminal for power supply (hereinbelow called simply "power source"). 
At first, the construction thereof will be explained. The control circuit 
1, in the state where the operation switch 21 is operated in order to 
carry out the detecting operation, continues to supply a scanning 
instructing signal s1, a light emission instructing signal s2 and a focus 
adjustment instructing signal s3 to the deflection control section 4, the 
light emission control section 2 and the focus adjusting control section 
6, respectively, by the fact that the operation switch 21 is once closed. 
To the control circuit 1 outputting these instructing signals s1, s2 and 
s3 a stop instructing signal ed from the output circuit 112 in the state 
where a decode signal dt is obtained in the decode section 11 and a pivot 
detecting signal eg from the galvano scanner 19 in the deflecting device 
are supplied. The device is so constructed that when either the stop 
instructing signal eg is supplied or pivot detecting signals eg are 
supplied more than a predetermined number of times, these instructing 
signals s1, s2 and s3 are interrupted. 
The pivot detecting signal eg and the scan drive instructing signal 4a, 
which is the same as the signal, which the control section 4, in which the 
scan instructing signal s1 is inputted, has supplied to the deflection 
driving circuit 5, is returned to this scan number setting section 101 in 
the control circuit 1. In the scanning counter 102 in the scan number 
setting section 101, the pivot detecting signal eg is supplied to its 
counting input terminal and the scan drive instructing signal 4a is 
supplied to its reset terminal. The scan drive instructing signal 4a 
resets the count number cn of the scanning counter 102 to its initial 
value at the same time as it instructs the pivot of the galvano scanner 19 
to the deflection driving circuit 5. The circuit is so constructed that 
pivot detecting signals eg outputted in the form of pulses of "H" level 
for every pivot period of the galvano scanner 19 are counted and the count 
number cn is supplied to the comparator 104. The circuit is so constructed 
that in the comparator 104 the count number cn is compared successively 
with the stored value cs previously set, corresponding to the maximum 
number of scannings for the scanner 19 and when they are in accordance 
with each other, the comparator 104 supplies the operation stop 
instructing signal s0 to the deflection control section 4, the light 
emission control section 2 and the focus adjusting control section 6 and 
at the same time interrupts the scanning instructing signal s1, the light 
emission instructing signal s2 and the focus adjustment instructing signal 
s3. 
The control circuit 1, in the state where the scanning instructing signal 
s1, the light emission instructing signal s2 and the focus adjustment 
instructing signal s3 are interrupted, is so constructed that these 
instructing signals s1, s2 and s3 are again outputted, when the operation 
switch 21 is again closed. 
The deflection control section 4, in the state where the scanning 
instructing signal s1 is supplied, continues to make the deflection 
driving circuit 5 output the deflection driving signal bi for making the 
galvano scanner 19 effect the pivoting operation by means of the scan 
drive instructing signal 4a and resets the scanning counter 102 in the 
state where the deflection driving signal bi rises. 
Further the circuit is so constructed that the pivot detecting signal eg 
outputted by the galvano scanner 19 is supplied to the deflection control 
section 4 and that under the condition that the scan instructing signal s1 
is supplied, a scanning period signal ST is supplied to the amplifying 
circuit 9 in synchronism with the rise of the pivot detecting signal eg to 
the "H" level. This scanning period signal ST falls to the "L" level, just 
before the sweep linear speed, with which the deflecting devices 18 and 19 
sweep the spot of the laser beam, goes out of the tolerated region 
therefor, to stop the amplifying and processing operation. When a 
predetermined period of time has lapsed, supposing that the linear sweep 
speed has been within the tolerated region, scanning period signal ST 
rises to the "H" level and is outputted to execute the amplifying and 
processing operation. 
The circuit is so constructed that the deflection driving circuit 5, in the 
state where the deflection driving signal bi is outputted, while the scan 
drive instructing signal 4a is supplied, interrupts the scan drive 
instructing signal 4a for interrupting the pivoting operation of the 
galvano scanner 19, when the operation stop instructing signal s0 is once 
supplied. 
When the deflection driving signal bi begins to be supplied, the galvano 
scanner 19 begins to move towards one end of the pivot region from the 
position not specified, where it has been stopped. The galvano scanner 19 
is so constructed that when it arrives at this end, it is returned so that 
it pivots forward and backward with a constant period and speed 
determined, depending on the mass, the resistance against the pivot, etc. 
of the mass consisting principally of the pivoting portion of the galvano 
scanner 19 and the pivoting reflecting mirror 18 mounted on this galvano 
scanner 19. A position detecting function is incorporated in this galvano 
scanner 19 to detect the pivot detecting signal eg rising to the "H" level 
at the position corresponding to the tolerated region of the linear sweep 
speed, with which the reflecting mirror 18 makes the spot of the laser 
beam sweep, for every scanning period to output it. 
The pivot detecting signal eg is supplied also to the light emission 
control section 2, in the state where the light emission instructing 
signal s2 is supplied. In this way an accident preventing construction is 
realized, in which the light emission control section 2 supplies the light 
emission drive instructing signal oe to the light emission driving circuit 
3 in synchronism with the second rise of the pivot detecting signal eg to 
the "H" level so that irradiation is not effected with a linear scanning 
speed of the laser spot at the start, which is lower than a predetermined 
value. For this accident preventing construction at the start it is 
sufficient that the number of pivot detecting signals eg is greater than 
1. It is so constructed that it contributes also to the stabilization of 
the reading speed and that the detecting operation time is not too long 
because of an excessively great number thereof. The accident preventing 
construction is realized by the fact that in the case where the repetition 
period of this pivot detecting signal eg is longer than a period 
previously set, the light emission control section 2 intercepts the light 
emission drive instructing signal oe so that irradiation is not effected 
with a linear scanning speed of the laser spot during the detection, which 
is lower than a predetermined value. 
The light emission driving circuit 3 is constructed so as to supply the 
light emission driving current to the light emission element 12 composed 
of a semiconductor laser diode for exciting it to emit a laser light beam 
during the period of time where the pivot detecting signal eg is supplied. 
The light emitting element 12 is constructed so as to irradiate the 
reflecting mirror 18 with the laser light beam having an intensity 
corresponding to the intensity of the light emission driving current 3a 
through the path consisting of the focus adjusting lens 14, the hole 
formed in the holed mirror 15 and the fixed lens 17 in this order, during 
the period of time the light emission driving current 3a flows 
therethrough. In this construction the laser beam projected to the 
reflecting mirror 18 forms a beam spot on the bar code representing 
surface 20 and is swept by the reflecting mirror 18 mounted so as to be 
pivoted with the galvano scanner 19. 
The focus adjusting control section 6 is constructed so as to supply the 
focus drive instructing signal 6a to the focus adjusting drive circuit 7 
for moving the focus adjusting lens 14 with a speed in a direction 
previously determined for the greatest number of pivots, which the galvano 
scanner effects, for every operation of the operation switch 21, during 
the period of time where the focus adjustment instructing signal s3 is 
supplied. 
The focus adjusting drive circuit 7, to which the focus drive instructing 
signal 6a is supplied, is constructed so as to supply the focus adjusting 
drive signal fc indicating the position, to which the focus adjusting lens 
14 is to be moved, corresponding to the value of the focus drive 
instructing signal 6a, to the focus adjusting device 13 having the voice 
coil, only during the period of time no operation interruption instructing 
signal s0 is supplied. The focus adjusting device 13, to which the focus 
adjusting drive signal fc is supplied, is constructed so as to move the 
focus adjusting lens 14 mounted on the actuator portion linked with the 
voice coil, through which current is made flow by the focus adjusting 
drive signal fc. 
The focusing position of the beam spot moved by the focus adjusting lens 14 
is constructed so as to be varied, corresponding to the pivot speed of the 
galvano scanner 19, depending on the intensity of the current flowing 
through the voice coil, and to be regulated mechanically. 
The device is so constructed that the laser light beam, whose focus is 
variable, is collected by the fixed lens 17 with collecting 
characteristics determined by the region of the diameter of the hole 
formed in the holed mirror. 
On the other hand, the device is so constructed that the laser light beam, 
with which the bar code representing surface 20 is irradiated, is 
collected and projected on the light sensitive surface of the light 
receiving element 16 composed of a PIN type photo-diode in the form of a 
reflected light beam corresponding to the reflection coefficient of the 
bar code representation through the path consisting of the pivoting 
reflecting mirror 18, the fixed lens 17 and the deflecting surface of the 
holed mirror 15. 
The device is so constructed that the light reception signal having a small 
amplitude corresponding to the intensity of the light thus collected, 
projected and reflected is supplied to the preamplifier 8, where it is 
compared with the reference voltage Vref supplied by the amplifying 
circuit 9 and amplified. The circuit is so constructed that the analogue 
signal es preamplified by the preamplifier 8, where it is compared with 
the reference voltage Vref and amplified, is supplied to the amplifying 
circuit 9 updating the amplification factor and the reference voltage Vref 
for the amplification operation according to the scanning period signal ST 
outputted by the deflection control section 4, corresponding to the 
pivoting operation of the galvano scanner 19. 
The circuit is so constructed that this amplifying circuit 9 supplies the 
value of the constant voltage Vs for setting the threshold value for the 
binary coding circuit 10; the divided voltage value Vr corresponding to 
the set threshold value is supplied; and this divided voltage value Vr 
generates a value of the reference voltage Vref, which is updated for 
every inputted scanning period signal ST, this reference voltage Vref 
serving as the reference for the amplifying operation by means of the 
preamplifier 8 and the amplifying circuit 9. This updating of the value of 
the reference voltage Vref is started by the fact that a pulse shaped 
scanning period signal ST is supplied from the deflection control section 
4 to the amplifying circuit 9, which signal is shifted to the "H" level on 
the basis of a pulse shaped pivot detection signal eg outputted by the 
galvano scanner 19, just before the linear sweep speed of the beam spot 
projected on the bar code representing surface 20 exceeds the tolerated 
variation value. Thus the circuit is so constructed that the amplifying 
circuit 9 continues to supply a high divided voltage value Vr to the 
binary coding circuit 10 for stopping the binary coding operation and a 
high value of the reference voltage Vref to the preamplifier 8 and the 
amplifying circuit 9 for stopping the amplifying operation. The device is 
so constructed that the pulse shaped scanning period signal ST, which is 
shifted from the "H" level to the "L" level for obtaining the value of the 
stationary divided voltage Vr for effecting the binary coding operation, 
is supplied from the deflection control section 4 to the amplifying 
circuit 9, in the state where the reflecting mirror 18 returns from this 
state to the pivoting center position. The amplifying circuit 9, to which 
the scanning period signal ST, which has been shifted to the "H" level, 
has been supplied, supplies immediately the stationary divided voltage 
value Vr to the binary coding circuit 10 and at the same time the value of 
the reference voltage Vref for the reference for the amplifying operation 
simulating the divided voltage value Vr at this time to the preamplifier 8 
and the amplifying circuit 9, before the linear scanning speed of the beam 
spot, with which the bar code representing surface 20 is irradiated, 
becomes a value within the tolerated variation region. The circuit is so 
constructed that the value of the reference voltage Vref updated in this 
way continues to be held during a certain period of time where the linear 
scanning speed of the beam spot, with which the bar code representing 
surface 20 is irradiated, is within the tolerated variation region and 
further that the value of the reference voltage Vref remains unchanged 
during a period of time until the scanning period signal ST shifted to the 
"H" level by the fact that the galvano scanner 19 is pivoted is supplied. 
The device is so constructed that the amplifying circuit 9, to which the 
scanning period signal ST shifted to the "H" level for every scanning 
period of the galvano scanner 19 is supplied, has a constant amplification 
factor, while the linear scanning speed of the beam spot is within the 
tolerated variation region and that the variation direction and the 
variation width of the amplification factor are previously set for every 
time when the scanning period signal ST is supplied. 
The device is so constructed that the binary coding circuit 10, to which 
the amplified signal Va from the amplifying circuit 9 with the constant 
amplification factor by the amplifying operation based on the updated 
value of the reference voltage Vref, processes the amplitude waveform of 
the amplified signal Va during a period of time where the stationary 
divided voltage value Vr to supply the binary signal di transformed into a 
rectangular wave of "H" and "L" level to the decode section 11. On the 
other hand the device is so constructed that during a period of time where 
a high value of the divided voltage Vr is supplied, the amplified signal 
Va in all the supplied states is cancelled and the binary coding circuit 
10 supplies a unchanged binary coded signal di to the decode section 11. 
The device is so constructed that the decode section 11, to which the 
binary coded signal di corresponding to the information represented by the 
bar code is supplied, transforms it into a bit image; further transforms 
each of the bit image data into character data; supplies the interruption 
instructing signal ed for interrupting the detection scanning, when it is 
judged that a set of start and stop code exists; and at the same time 
supplies the character data to a host computer not indicated in the figure 
in the form of the decoded signal. On the other hand the device is so 
constructed that in the state where no decoded signal dt can be outputted 
from the point of time where the binary coded signal di is supplied for 
the first time to the point of time previously set, corresponding to the 
pivoting speed of the galvano scanner 19, the decode section 11 cancels 
the supplied binary coded signal di, supposing that it contains no 
necessary information and thus no coded signal dt is outputted to the host 
computer. 
Next the construction of an embodiment of the signal processing from the 
light emitting element 16 to the binary coding circuit 10 will be 
explained, referring to FIG. 13. 
The cathode of the light emitting element 16 is connected with the power 
source Vcc, whose negative pole is grounded through the common ground line 
and the connection of this cathode with the power source Vcc is grounded 
through the noise bypassing capacitor C1 for removing undesirable noise 
having short periods. The anode of the light receiving element 16 is 
connected with the inverting input terminal - of the operational amplifier 
81, which is the input terminal of the preamplifier 8. The resistance R1 
for the current feedback is connected between this inverting input 
terminal - and the output terminal of the operational amplifier 81. The 
value of the reference voltage Vref having two states outputted by the 
reference voltage generating section 91 is applied to the non-inverting 
terminal + of the operational amplifier 81. A same value as this value of 
the reference voltage Vref serves as the operation reference potential. 
The circuit is constructed as a current - voltage transforming circuit 
generating an output voltage, in which variations in the impedance between 
the cathode and the anode of the light receiving element 16 are superposed 
on this operation reference potential. The value of the output voltage V81 
of this current - voltage transforming circuit is so constructed that 
according to increase and decrease in the intensity of the received light, 
the impedance from the cathode to the anode of the light receiving element 
16 is lowered and raised and the intensity of the input current, which is 
made flow through the path of power source Vcc .fwdarw. cathode and anode 
of of the light receiving element 16 .fwdarw. inverting input terminal - 
of the operational amplifier 81 .fwdarw. resistance R1 .fwdarw. inverting 
input terminal - of the operational amplifier 81.fwdarw.negative pole 
power source terminal not shown in the figure of the operational amplifier 
81 .fwdarw. ground in this direction, increases and decreases, 
respectively, so that a value of the product of variations in this current 
.DELTA.I and the current feedback resistance R1 is superposed on a same 
value as the value of the reference voltage Vref according to the 
relationship given by; 
EQU V81=Vref+.DELTA.I.multidot.R1 
The value of the output voltage Vo from the output terminal of this 
operational amplifier 81 is grounded through the capacitor C2 and the 
resistance R2. All of the cathode of the diode D1, the inverting input 
terminal - of the operational amplifier 82 and the non-inverting input 
terminal + of the operational amplifier 83 are connected with the common 
connection point between the capacitor C2 and the resistance R2. The anode 
of the diode D1 and the output terminal of the operational amplifier 82 
are connected with each other and thus the ideal diode circuit, in which 
the value of the reference voltage Vref is applied to the non-inverting 
input terminal + of the operational amplifier 82, forms a clamp circuit 
working together with the capacitor C2 by using the value of the reference 
voltage Vref as the working potential. A processing voltage value V82 
obtained by the fact that the value of the output voltage V81 of the 
current--voltage transforming circuit is clamped along the value of the 
reference voltage Vref on the "L" level side, when black bars, for which 
the intensity of the reflected light is weak, on the bar code representing 
surface 20 are read out by this clamp circuit, is applied to the 
non-inverting input terminal + of the operational amplifier 82. The 
resistance R3 for the negative feedback is connected between the inverting 
input terminal - of this operational amplifier 82 and the output terminal 
and the value of the reference voltage Vref is applied to this inverting 
input terminal - through the resistance R4. The value of the amplified 
voltage V83 of this operational amplifier 82 is outputted with the same 
polarity according to the ratio of the voltage division determined by the 
resistance R3 and the resistance R4 by dividing the value of the 
processing voltage V82, for which the "L" level side is clamped along the 
value of the reference voltage Vref, using the value of the voltage 
reference Vref as the working potential, as expressed by; 
EQU V83=V82.multidot.(R3/R4+1) 
This value of the amplified voltage V83 is grounded through a series 
circuit consisting of the capacitor C3 and the resistance R5 and the ideal 
diode circuit is connected with the common connecting point between the 
capacitor C3 and the resistance R5, which circuit consists of the diode D2 
and the operational amplifier 84 and works just as the diode D1 and the 
operational amplifier 82. The capacitor C3 and this ideal diode circuit 
are connected so that they work just as the set of the capacitor C3 and 
the ideal diode circuit clamping the value of the output voltage V8. Thus 
the value of the voltage obtained by processing the value of the voltage 
V83 by means of this clamp circuit is supplied to the amplifying circuit 9 
as the analogue signal es, whose voltage increases with the increasing 
intensity of the reflected light obtained by the fact that it is 
preamplified by the preamplifier 8 and the "L" level side thereof is 
clamp-processed along the value of the reference voltage Vref. 
The operational amplifier 96 is disposed in the amplifying section 90 of 
the amplifying circuit 9, in which amplifier the analogue signal es is 
applied to the non-inverting input terminal +. The resistance R6 for the 
negative feedback is connected between the output terminal and the 
inverting input terminal - of this operational amplifier 96. 
One end of the resistances R8 to R10 disposed in the feedback quantity 
setting section 92 is connected with the inverting input terminal - of the 
operational amplifier 96, to which this resistance R6 is connected. 
The other end of each of the resistances R8 to R10 disposed in the feedback 
quantity setting section 92 is connected with one end of each of the 
switches Sc0 to Sc3 disposed in the selecting section 93. The value of the 
reference voltage Vref outputted by the reference voltage generating 
section 91 disposed in the amplifying circuit 9 is applied to the other 
end of these switches Sc0 to Sc3. 
This reference voltage generating section 91 is so constructed that two 
kinds of values of the reference voltage Vref are outputted, referring to 
the constant voltage value Vs outputted by the constant voltage power 
source section 95 disposed in the amplifying circuit 9 according to the 
scanning period signal ST supplied from the deflection control section 4, 
which is shifted to the "L" and the "H" level for every scanning period of 
the galvano scanner, and the divided voltage value Vr, which sets the 
binary coding operation of the binary coding circuit 10 on the basis of 
this constant voltage value Vs by means of the resistances R12 to R15. 
The scanning period signal ST from the deflection control section 4 is 
applied to the base of the transistor Q1 disposed in the reference voltage 
generating section 91 through the resistance R18. The resistance R17 for 
setting the input impedance is connected between the base and the emitter 
of this transistor Q1. The constant voltage value Vs outputted always at a 
constant voltage by the reference voltage generating section 91 is applied 
always to the emitter of this transistor Q1. One end of the resistance R16 
disposed in the reference voltage generating section 91, the non-inverting 
input terminal + of the operational amplifier 34 and one end of the 
resistance R15 in the binary coding circuit 10 are all connected with the 
cathode of the transistor Q1 and the other end of the resistance R16 is 
grounded. The inverting input terminal - of this operational amplifier 4 
is grounded through the capacitor C5 set at a relatively large 
electrostatic capacitance and the output terminal of the operational 
amplifier 34 is so connected that the negative feedback is effected 
therefrom through the resistance R19. The common connecting point of the 
resistance R19, the capacitor C5 and the inverting input terminal - of the 
operational amplifier 34 serves as the output terminal for outputting the 
value of the reference voltage Vref of the reference voltage generating 
section 91. 
The circuit is so constructed that the common connecting point of one end 
of the resistance R16 disposed in the reference voltage generating section 
91 and the non-inverting input terminal + of the operational amplifier 34 
serves as the input terminal for referring to the binary coded reference 
voltage of the binary coding circuit 10 so that the constant voltage value 
Vs outputted by the constant voltage power source section 95 disposed in 
the amplifying circuit 9 is applied thereto through a series circuit 
consisting of the resistances R12 to R15 disposed in the binary coding 
circuit 10. 
In the transistor Q1 during the period of time where the deflection control 
section 4 applies the scanning period signal ST of "L" level to the base 
thereof, since the base current Ib is made flow through the transistor 
from the emitter to the base, the collector current Ic is made flow 
through the transistor Q1 from the emitter to the collector and this 
collector Ic flows through the resistor R16 to the ground line. During the 
period of time where the collector current Ic is made flow through the 
transistor Q1, representing the emitter--collector voltage allotted 
between the emitter and the collector of the transistor Q1 by the voltage 
division by Vce, a divided voltage value Vr(R), which is a high value 
close to the constant voltage value Vs, as expressed by the following 
equation, which is determined approximately by the product of the 
collector current value Ic and the value of the resistance R16, is applied 
to the non-inverting input terminal + of the operational amplifier 34, 
because the value of the series resistance circuit consisting of the 
resistances R12 to R15 is 1.5 to 4 times as great as that of the 
resistance R16 and the voltage Vce as well as the impedance Rce between 
the emitter and the collector are relatively low; 
##EQU1## 
The operational amplifier 34, in which the high voltage value Vr(R) 
allotted by the voltage division is applied to the non-inverting input 
terminal +, makes the negative feedback current flow through the 
resistance R19 from the output terminal thereof, until the voltage between 
the two terminals of the capacitor C5 connected with the inverting input 
terminal - arrives at the divided voltage value Vr(R). The time measured 
from the point of time where this negative feedback current begins to flow 
to the point of time where the voltage arrives at the value of the 
reference voltage Vref(R), which is equal to the divided voltage value 
Vr(R), is set to a relatively short charging time determined by the time 
constant of the resistance R19 and the capacitor C5. The circuit is so 
constructed that this reference voltage value Vref(R) is maintained only 
during the period of time where the voltage applied to the non-inverting 
input terminal + of the operational amplifier 34 is equal to the divided 
voltage value Vr(R). 
In the transistor Q1 during the period of time where the deflection control 
section 4 applies the scanning period signal ST of "H" level to the base 
thereof, the base current Ib flowing through the transistor Q1 from the 
emitter to the base is interrupted and the collector current Ic, which was 
made flow through the transistor Q1 from the emitter to the collector. In 
the state where the collector current Ic is interrupted, a divided voltage 
value Vr(F), which is a relatively low value close to the ground line 
side, as expressed by the following equation, obtained by dividing the 
constant voltage value Vs by the resistance ratio of the resistance R16 to 
the series resistance circuit consisting of the resistances R12 to R15, 
which is 1.5 to 4 times as great as that of the resistance R16, is applied 
to the non-inverting input terminal + of the operational amplifier 34 in 
the state where the collector current Ic is interrupted, because the 
emitter--collector voltage Vce allotted by the voltage division to the 
transistor Q1 between the emitter and the collector is extremely close to 
the constant voltage value Vs; 
EQU Vr(F)=R16.multidot.[Vs/(R12+R13+R14+R15+R16)] 
The operational amplifier 34, in which the low voltage value Vr(F) is 
applied to the non-inverting input terminal +, makes the negative feedback 
current flow through the resistance R19 from the capacitor C5, until the 
voltage between the two terminals of the capacitor C5 connected with the 
inverting input terminal - arrives at the divided voltage value Vr(F). The 
time measured from the point of time where this negative feedback current 
begins to flow to the point of time where the voltage arrives at the value 
of the reference voltage Vref(F), which is equal to the divided voltage 
value Vr(F), is set to a relatively short charging time determined by the 
time constant of the resistance R19 and the capacitor C5. The circuit is 
so constructed that this reference voltage value Vref(F) is maintained 
only the period of time where the voltage applied to the non-inverting 
input terminal + of the operational amplifier 34 is equal to the divided 
voltage value Vr(F). 
The circuit is so constructed that the switches Sc0 to Sc3 effect the 
closing operation according to the closing instruction from the counter 94 
disposed in the amplifying circuit 9 and vary the value of the impedance 
between the non-inverting input terminal - of the operational amplifier 96 
and the point, to which the reference voltage Vref is applied among 16 
values at maximum. 
The circuit is so constructed that the scanning period signal ST outputted 
by the deflection control section 4, which is shifted to the "H" level for 
every scanning period of the galvano scanner 19 is supplied to the counter 
94, which issues the closing instruction to the switches Sc0 to Sc3, so 
that the amplification factor is constant only during the period of time 
where the linear scanning speed of the beam spot is in the tolerated 
variation region and that the amplification factor is renewed and it is 
operated with a constant amplification factor, when the linear scanning 
speed of the beam spot has become once out of the tolerated variation 
region and returns to a value within the tolerated variation region. This 
counter 94 is constructed so as to update the count number step by step by 
shifting the level from "L" to "H" for every scanning period of the 
galvano scanner 19 and to issue the opening and closing instruction to 
each of the switches by the output state to four closing instruction lines 
representing this updated count number. 
The circuit is so constructed that during the period of time where the 
linear scanning speed of the beam spot is within the tolerated variation 
region, the amplified signal Va outputted by the amplifying section 90 
according to the opening and closing operation of the switches Sc0 to Sc3 
is outputted in the same polarity according to the following equation, 
using an amplification factor set by the resistance R6 and the resultant 
resistance Rz of the resistances R8 to R10 according to the opening and 
closing operation of the switches Sc0 to Sc3 and the reference voltage 
value Vref as the working voltage; 
EQU Va=es.multidot.(R6/Rz+1) 
The circuit is so constructed that the constant voltage power source 
disposed in the amplifying circuit 9 is grounded through the capacitor C6 
for bypassing relatively slow variations in the voltage of the power 
source Vcc and the capacitor for bypassing relatively fast variations in 
the voltage in order to effect the smoothing operation. This power source 
voltage value Vcc thus processed by bypassing voltage variations is 
applied to the input terminal of the constant voltage power source element 
VR of semiconductor three terminal type. The ground terminal of this 
constant voltage power source element VR is connected with the ground line 
so that the constant voltage value Vs outputted from this output terminal 
is grounded through the noise bypassing capacitor C8 for removing the 
pulse-like noise component. The circuit is so constructed that the 
constant voltage value Vs processed by bypassing voltage variations by 
means of this capacitor C8 is lower than the power source voltage value 
Vcc by a predetermined value and that the constant voltage value Vs 
stabilized within the nominal current consumption of the constant voltage 
power source element VR is supplied to one end of the resistor R12 in the 
binary coding circuit 10 as well as to the connection between the emitter 
of the transistor Q1 and the resistance R17 disposed in the reference 
voltage generating circuit 91. 
The amplified signal Va supplied to the binary coding circuit 10 is 
grounded through a series circuit consisting of the capacitor C4 and the 
resistance R11. The inverting input terminals - of the operational 
amplifiers 30, 31 and 32 as well as the anode and the cathode of the 
diodes D3 and D4, respectively, are connected with the connection between 
this capacitor C4 and the resistance R11. The non-inverting input terminal 
+ of the operational amplifier 31 is connected with the common connecting 
point between the resistance R12 and the resistance R13 among the 
resistances R12 to R16 connected in series between the constant voltage 
value Vs and the ground line. This output terminal is connected with the 
cathode of the diode D3 so that the diode D3 and the operational amplifier 
31 constitute an ideal diode circuit and thus an upper clamp circuit is 
constituted by this ideal diode circuit and the capacitor C4, which upper 
clamp circuit clamps the high voltage value side of the supplied amplified 
signal Va with the upper clamp voltage value indicated by the following 
equation; 
EQU V10h=(R13+R14+R15+R16).multidot.Vs/ (R12+R13+R14+R15+R16) 
The non-inverting input terminal + of the amplifier 32 is connected with 
the common connecting point between the resistance R14 and the resistance 
R15 among the resistances R12 to R16 connected in series between the 
constant voltage value Vs and the ground line and the output terminal 
thereof is connected with the anode of the diode D4 so that the diode D4 
and the operational amplifier 32 constitute an ideal diode circuit. This 
ideal diode circuit and the capacitor C4 constitute a lower limit clamp 
circuit, which clamps the low voltage side of the supplied amplified 
signal Va expressed by the following equation; 
EQU V10l=(R15+R16).multidot.Vs/(R12+R13+R14+R15+R16) 
The resistances R12 to R15 as well as the resistance 16, which are 
connected in series, are set to high impedance values so that their 
resistance is not varied by heat produced by the current flowing 
therethrough. Further the state of these resistances R12 to R15 connected 
in series is monitored by monitoring the divided voltage value Vr(F), 
which is the voltage value appearing between the two terminals of the 
resistance R16, and the signal thus obtained is supplied to the 
preamplifier 8 and the selecting section 93 in the amplifying circuit 9 as 
the reference voltage Vref(F) only during the period of time where the 
scanning period signal ST of "H" level is supplied. In this way the 
amplified signal Va, which is signal-processed along this reference 
voltage value Vref(F), is supplied. 
The non-inverting input terminal + of the operational amplifier 33 is 
connected with the common connecting point between the resistance R13 and 
the resistance R13 among the resistances R12 to R15 and the resistance 16 
connected in series and the output terminal and the inverting input 
terminal - thereof are directly connected with each other so that the 
central voltage value V10m between the upper clamped voltage value V10h 
and the lower clamped voltage value V10l is buffer-amplified and that they 
are outputted with a same value. This central voltage value V10m thus 
buffer-amplified is applied to the non-inverting input terminal + of the 
operational amplifier 30 through the resistance R20. The resistance R21 
for the positive feedback is inserted between the output terminal and the 
non-inverting input terminal + of this operational amplifier 30 so that 
the binary coding operation is executed around the central voltage value 
V10m. When the clamped voltage V10, whose upper and lower extremities are 
clamp-processed and which is applied to the non-inverting input terminal 
-, has once exceeded the voltage value applied to the non-inverting input 
terminal + of the operational amplifier 30, this operational amplifier 30 
outputs a signal of "L" level through the output terminal thereof and at 
the same time lowers further the voltage value applied to the 
non-inverting input terminal + towards the ground potential side. On the 
contrary, when the clamped voltage V10, whose upper and lower extremities 
are clamp-processed and which is applied to the non-inverting input 
terminal -, has once become lower than the voltage value applied to the 
non-inverting input terminal + of the operational amplifier 30, this 
operational amplifier 30 outputs a signal of "H" level through the output 
terminal thereof and at the same time raises further the voltage value 
applied to the non-inverting input terminal + towards the power source 
voltage value Vcc side. The output terminal of the operational amplifier 
30, which is updated for every inversion of such two stable threshold 
values is constructed as the output terminal of the binary coding circuit 
supplying the binary decoded signal di to the decode circuit 111. 
On the other hand, in the binary coding circuit 10, to which the high 
divided voltage value Vr(R) is applied, since the voltage difference 
between the upper clamped voltage value V10h and the lower clamped voltage 
value V10l is small by the fact that relatively low voltage Vce between 
the emitter and the collector in the state where the collector current Ic 
is made flow through the transistor Q1 is applied between the two 
terminals of the resistances R12 to R15 connected in series and the 
central voltage value V10m is shifted significantly towards the power 
source voltage Vcc side because of the fact that the divided voltage value 
Vr(R) is not high, the supplied amplified signal Va is not binary coded. 
In this way the circuit is so constructed that a binary coded signal di in 
the state where it is always at the "H" level and not shifted is outputted 
so that it is prevented that the processing time necessary for the 
succeeding decoding operation is elongated or the processing becomes 
impossible. 
Although in the embodiments explained above the means for selecting and 
setting the amplification factor is constructed so as to vary the 
amplification factor for every pivot of the galvano scanner 19, the 
present invention is not limited thereto, but it may be so constructed 
that the amplification factor is varied once for a plurality of pivots of 
the galvano scanner 19. 
Further, if this means for selecting and setting the amplification factor 
keeps the amplification factor constant during a period of time where 
reading out is effected with a linear speed of the pivot of the galvano 
scanner 19 is within the tolerated region, it is not limited to means 
varying it stepwise, but it may be constructed so as to vary it 
continuously. 
As explained above, according to the present invention having the first 
technical means, since the focusing position adjusting mechanism is 
controlled by the fact that the bar code is correctly decoded, it is 
possible to provide a laser scanner having excellent functions that the 
bar code is read out at a focusing position, where reading out can be 
effected, corresponding to the printing quality of the bar code and the 
surface state of the recording medium and that the reading probability is 
significantly improved. 
As explained above, according to the present invention having the second 
technical means, since the device is so constructed that the normal 
driving current is controlled by the driving element 18 controlling the 
driving current and at the same time and that it includes initiation 
detecting means 100 and control means 300 capable of making this element 
18 carry out a soft start operation at the starting so that no useless 
voltage divided in series in the laser diode De, the applied power source 
voltage can be utilized with a high efficiency and therefore a stable 
operation can be obtained even by setting the power source voltage at a 
low value. 
As explained above, according to the present invention having the third 
technical means, since the comparing circuit executes a stable holding 
operation by utilizing the result obtained by comparing the input voltage 
to be compared with the reference voltage through the diode inserted at 
least in one of the positive feedback circuit and the input circuit, an 
effect can be obtained that a comparing circuit with a holding function is 
provided, which can be formed in one-chip-analogue-IC and mounted on a 
small mounting board and which is suitable for small portable apparatuses, 
etc. 
As explained above, according to the present invention having the fourth 
technical means, since the device is so constructed that the amplification 
factor is fixed during one period for scanning and detecting the code and 
that the amplification factor is varied for different scanning periods, 
the signal processing can be effected with the optimum amplification 
factor and the code can be read out in a wide recording state. 
Furthermore, in a code reading device such as a hand held device, for 
which the power source voltage is restricted, an effect can be obtained 
that desired processed signals are obtained by utilizing the width of the 
power souce with a high efficiency for the amplifying and the binary 
coding operation, etc.