Printing device

The present invention relates to a printing device having a carriage and a serial-impact printing unit carried by the carriage, wherein characters are printed on a recording medium by the printing unit after the carriage has been moved to and positioned at predetermined printing positions in a printing direction. The printing device has a judging device for checking if the printing device is placed in a precise-positioning mode which is selected when relatively high positioning accuracy of the carriage is required, or in a normal-positioning mode which is selected when there is a relatively wide range of positioning tolerance of the carriage; and a switching device, responsive to the judging device, for effecting a printing operation at a comparatively low printing speed when the judging device has judged that the printing device is placed in the precise-positioning mode, and for effecting the printing operation at a comparatively high printing speed when the judging device has judged that the printing device is placed in the normal-positioning mode.

BACKGROUND OF THE INVENTION 
1. Field of the Art 
The present invention relates to a serial-impact printing device having 
character fonts or type elements, for example on a daisy type wheel, 
wherein a carriage which carries printing means, including such a type 
wheel, is moved along a line of printing to bring a desired character into 
a predetermined printing position. The positioned character is impacted 
subsequently on a recording medium, whereby successive characters are 
printed, one character at a time. 
2. Related Art Statement 
Such a serial-impact printing device is versatile, in that it may be used 
as a printer for printing data which is transferred from an external input 
device via an input connector, and also as a typewriter for printing data 
while the data is entered through a keyboard connected thereto. In either 
case, the printer is operated in a normal printing mode or in a special 
printing mode. In the normal printing mode, the characters are printed in 
a normal fashion-by means of intermittent movements of the carriage to 
successive printing positions. In the special printing mode, the 
characters are boldface-printed or shadow-printed for accentuation, or 
vertical lines are scored as for tabulation. 
This type of serial-impact printer starts a printing action only after the 
carriage has been positioned at the appropriate printing position, and 
therefore suffers difficulty in speeding the printing operation. More 
specifically described, when a character is printed at printing position 
"b" of FIG. 5, the carriage is moved from the preceding position "a" to 
the printing position "b" by a one-character spacing. As indicated by 
curves C1 and C2 in the figure, the carriage undergoes a transient 
vibrational movement around the printing position "b", whose amplitude is 
gradually reduced to zero, with a result of the carriage being finally 
positioned at the predetermined position "b". The printing means is 
inhibited from starting its printing action until the transient phenomenon 
is thoroughly removed, i.e., until a point of time "t4" is reached, 
whereat the impacting action against the sheet of paper is started by the 
printing means. Accordingly, the waiting time of the printing means 
reduces the printing efficiency or speed of the printer. 
Various attempts have been made to speed up the printing speed, i.e., to 
increase the number of characters printable per unit time. An example of 
such attempts is disclosed in Japanese Patent Application which was laid 
open in 1983 under Publication No. 58-67484. In a serial printer proposed 
in this application, the rate of movement of the carriage and the 
actuation timing of the print hammer are variably controlled depending 
upon a distance of movement of the carriage. 
When characters are printed on paper in a normal manner with intermittent 
movements of the carriage, the characters do not generally give an 
unpleasant impression or appearance to the readers, even though the 
characters are deviated from their normal printing positions by a distance 
less than one tenth of a character-to-character spacing. On the contrary, 
the readers are likely to feel displeased with boldfaced or shadowed 
characters or vertical scores even when the specially printed characters 
or vertical scores are deviated only a slight distance from their normal 
positions. Thus, even a small amount of deviation of the carriage from the 
predetermined positions will degrade the impression or appearance of the 
boldfaced or shadowed characters, or vertical lines, and thus lower the 
printing quality in the special printing mode. 
In the case where the printing device is used as a typewriter, it is 
required to correct or erase sets of characters or words which have been 
erroneously entered and printed. If the characters to be corrected are 
deviated from their normal positions, it is impossible to achieve perfect 
erasure or neat correction or replacement of the characters. When the 
printing device is operated as a printer, characters are merely printed 
and the correction of the printed characters is not necessary and 
impossible. In this case, non-special, ordinary characters will not give 
an unpleasant impression on the readers, even if the printed characters 
are slightly deviated from their normal positions. 
It will be understood that the length of waiting time of the printing means 
required for substantial removal of the transient vibrational movement of 
the carriage at each commanded printing position, will differ depending 
upon the specific printing modes, that is, whether the printing device is 
operated in the special-printing mode for effecting a special printing 
such as boldfaced printing, shadow printing and vertical scoring, and 
whether the printing device is operated in the typewriter mode or in the 
printer mode. Accordingly, the use of constant length of waiting time 
before starting the impacting action without regards to the specific 
printing modes will lower the overall printing efficiency or printing 
speed of the printing device. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a printing 
device having a carriage and serial-impact printing means carried by the 
carriage, having an improved printing speed, without lowering the printing 
quality. 
According to the invention, there is provided a printing device having a 
carriage and serial-impact printing means carried by the carriage, wherein 
characters are printed on a recording medium by the printing means after 
the carriage has been moved to and positioned at predetermined printing 
positions in a printing direction, the printing device comprising judging 
means and switching means. The judging means checks if the printing device 
is placed in a precise-positioning mode which is selected when relatively 
high positioning accuracy of the carriage is required, or in a 
normal-positioning mode which is selected when there is a relatively wide 
range of positioning tolereance of the carriage. The switching means, 
which is responsive to the judging means, operates to effect a printing 
operation at a comparatively low printing speed when the judging means has 
judged that the printing device is placed in the precise-positioning mode, 
and effect the printing operation at a comparatively high printing speed 
when the judging means has judged that the printing device is placed in 
the normal-positioning mode. 
In the printing device of the present invention constructed as described 
above, the printing operation is effected at a comparatively low speed in 
the precise-positioning mode, and at a comparatively high speed in the 
normal-positioning mode. The precise-positioning mode is selected when it 
is required to position the carriage and a selected type font or element 
of the serial-impact printing means relatively accurately at the 
predetermined printing position at which the corresponding character is to 
be printed. The normal-positioning mode is selected when a slight amount 
of deviation of the carriage from the predetermined printing positions 
will not appreciably affect the printing quality, that is when there is a 
relatively wide range of positioning tolerance of the carriage. According 
to this arrangement of the invention, the overall printing speed is 
increased, without substantively sacrificing the printing quality. 
The term "printing speed" used herein is interpreted to mean the number of 
characters printable per unit time, which is affected by the rate of 
movement of the carriage, and by the waiting time of the printing means 
after the carriage movement command is removed, and before the printing 
means starts an impacting action to print the selected character on the 
recording medium. Therefore, the printing speed is determined by the 
movement rate of the carriage and the waiting time of the printing means. 
According to an advantageous embodiment of the invention, the judging means 
checks if the printing device is placed in a typewriter mode or in a 
printer mode. In the typewriter mode, the characters are printed and/or 
corrected while the characters are entered. In the printer mode, the 
characters are printed after the characters have been entered and/or 
edited. The judging means judges that the printing device is placed in the 
precise-positioning mode when the typewriter mode is selected, and judges 
that the printing device is placed in the normal-positioning mode when the 
printer mode is selected. It will be understood that the typewriter mode 
of printing requires relatively precise positioning of the carriage to 
assure perfect correction or erasure of the printed characters, while the 
printer mode of printing operation requires relatively low positioning 
accuracy of the carriage, as the printer mode does not allow the printed 
characters to be corrected. 
According to another advantageous embodiment of the invention, the judging 
means checks if the printing device is placed in a special-printing mode 
or in a normal-printing mode. In the special-printing mode, the characters 
are printed in boldface or shadow fashion, or vertical lines are scored. 
In the normal-printing modes, the characters are normally printed. The 
judging means judges that the printing device is placed in the 
precise-positioning mode when the special-printing mode is selected, and 
judges that the printing device is placed in the normal-positioning mode 
when the normal-printing mode is selected. In this arrangement, the 
special printing is effected at a relatively low speed, while the normal 
printing is performed at a relatively high speed. Therefore, the overall 
printing speed is increased while maintaining the printing quality. 
According to one aspect of the invention, the switching means determines, 
based on the currently selected precise- or normal-positioning mode, the 
length of the waiting time of the printing means between the end of each 
movement of the carriage to the corresponding predetermined position, and 
the start of printing of the corresponding character. More specifically, 
the switching means is adapted to set the waiting time to be comparatively 
long when the judging means has judged that the printing device is placed 
in the precise-positioning mode, and to set the waiting time to be 
comparatively short when the judging means has judged that the printing 
device is placed in the normal positioning mode. 
According to another aspect of the invention, the switching means 
determines the rate of movement of the carriage, based on the currently 
selected positioning mode, precise- or normal-positioning mode. When the 
judging means has judged that the precise-positioning mode is selected, 
the switching means selects a comparatively low rate of movement of the 
carriage. When the normal-positioning mode is selected, the switching 
means selects a comparatively high rate of movement of the carriage. 
It is appreciated that both the waiting time of the printing means and the 
movement rate of the carriage be controlled depending upon the currently 
selected positioning mode, as described above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
To further clarify the concept of the present invention, a preferred 
embodiment of the invention will be described in detail, referring to 
FIGS. 1-5 of the accompanying drawing. 
There is schematically shown in FIG. 1 a printer section of a serial-impact 
printing device embodying the invention, wherein reference numeral 1 
designates an elongate platen which is rotatably supported on a printer 
frame 3 to hold a recording medium in the form of a sheet of paper 5. The 
platen 1 is rotated by a paper feed motor 7 via a gear train 9 which 
connects the motor 7 and the platen 1. With the platen 1 rotated, the 
sheet of paper 5 is fed in a direction perpendicular to an axis of 
rotation of the platen 1, i.e., in a direction perpendicular to a line of 
printing on the paper 5. 
A pair of spaced-apart parallel guide rods 11 are secured to the printer 
frame 3 so as to extend in parallel with the platen 1. The guide rods 11 
support a carriage 13 so that the carriage 13 is slidably movable along 
the platen 1 in opposed relation with the sheet of paper 5. The carriage 
13 is reciprocated by a carriage drive stepper motor 15 located behind the 
platen 1, via a wire 17 which transmits a rotary motion of the carriage 
drive motor 15 to the carriage 13. 
The carriage 13 carries a daisy type wheel 19 which is accommodated 
rotatably in a cartridge casing 21. As illustrated in FIG. 2, the type 
wheel 19 has a multiplicity of radial arms 23 which carry at their free 
ends multiple character fonts or type elements 25 which correspond to 
characters such as letters of a language or languages, numerals and 
various symbols. Thus, the type elements 25 are disposed along the outer 
circumference of the type wheel 19. 
The daisy type wheel 19 is rotated by a wheel drive stepper motor 27 
mounted on the carriage 13. The type wheel 19 is removably coupled to a 
rotor 27a of the stepper motor 27. Upon selection of a desired character, 
the type wheel 27 is indexed by the motor 27 by a suitable angle from a 
predetermined reference position, so that the corresponding type element 
25 is brought into printing position. 
The selected type element 25 which has been brought into the printing 
position by the wheel drive motor 27, is impacted by a print hammer 29 
against the sheet of paper 5 via a ribbon 31, with an impact pressure 
suitable for the selected type element 25. The ribbon 31 is fed by a 
ribbon feed motor 33 (FIG. 3) between the selected type element 25 and the 
sheet of paper 5. Thus, the desired characters are printed in succession 
on the paper 5 along the line of printing parallel to the axis of the 
platen 1, while the carriage 13 is moved intermittently. 
As is apparent from the foregoing description, the type wheel 19, wheel 
drive motor 27, print hammber 29, etc. constitute serial-impact printing 
means carried by the carriage 13 for printing the selected characters on 
the sheet of paper 5. 
Referring to FIG. 3, the control system of the printing device uses a 
central processing unit 35 (hereinafter referred to as "CPU 35"). The 
previously described paper feed motor 7, carriage drive motor 15, wheel 
drive motor 27 and ribbon feed motor 33 are connected to motor driver 
circuits 37, 39, 41 and 43, respectively, while the print hammer 29 is 
connected to a hammer driver circuit 45. These driver circuits 37, 39, 41, 
43 and 45 are connected to the CPU 35, so that the motors 7, 15, 27 and 
33, and the print hammer 29 are controlled by the CPU 35 through the 
respective driver circuits 37, 39, 41, 43, 45. 
The printing device is provided with a keyboard 47 connected to the CPU 35. 
The keyboard 47 has a multiplicity of character keys corresponding to the 
characters printed by the type elements 25, and various function keys 
which include a BOLDFACE key 49a, a SHADOW key 49b, a VERTICAL SCORE key 
49c and a PRINTER/TYPEWRITER selector key 49d. 
The BOLDFACE key 49a is used to effect a boldfaced printing in which the 
selected characters are printed in a boldfaced fashion. The SHADOW key 49b 
is used to effect a shadow printing in which the selected characters are 
printed by impacting the corresponding type elements 25 twice with the 
first and second impact positions being shifted a very small distance so 
that the two impressions overlap with each. The VERTICAL SCORE key 49c is 
turned on when vertical lines are scored. 
The printing device is operable in one of two printing modes, PRINTER mode 
and TYPEWRITER mode, which are selected by the PRINTER/TYPEWRITER selector 
key 49d. In the PRINTER mode, the characters which have been already 
stored in a random-access memory 51 (hereinafter referred to as "RAM 51"), 
are printed in a continuous manner. In this mode, it is impossible to 
correct the printed characters. In the TYPEWRITER mode, the desired 
characters are printed and/or corrected while they are entered through the 
keyboard 47, as in an ordinary typewriter. 
The above-indicated RAM 51, and a read-only memory 53 (hereinafter ROM 53) 
are connected to the CPU 35. The CPU 35 operates to process various 
signals, using the RAM 51 and the ROM 53. 
Upon depression of the character keys on the keyboard 47, corresponding 
character signals are applied to the CPU 35. Furthermore, the CPU 35 
receives BOLDFACE, SHADOW, VERTICAL SCORE and MODE signals, when the 
corresponding keys 49a, 49b, 49c and 49d are operated. The above-indicated 
signals from the keyboard 35 are coded by the CPU 35, and the coded signal 
is stored in the RAM 51. SPECIAL-PRINTING data indicative of the 
activation of the key 49a, 49b, 49c is stored at a bit 51a, while MODE 
data representative of the PRINTER or TYPEWRITER mode selected by the 
selector key 49d is stored at another bit 51b. 
In the instant embodiment, the content of the bit 51a is "1" when any one 
of the BOLDFACE, SHADOW and VERTICAL SCORE keys 49a, 49b, 49c is 
activated. When none of these keys 49a, 49b, 49c are activated, the 
content of the bit 51a is "0". When the PRINTER/TYPEWRITER selector key 
49d is set in the PRINTER mode position, the content of the bit 51b is 
"1". When the TYPEWRITER mode is selected by the selector key 49d, the 
content of the bit 51b is "0". 
Based on the SPECIAL-PRINTING data and MODE data, i.e., on the current 
contents of the bits 51a, 51b, the CPU 35 judges whether the carriage 13 
should be positioned at the predetermined printing positions with 
relatively high accuracy, or there is a relatively wide range of 
tolerances in positioning the carriage 13. In other words, the CPU 35 
judges that the printing device is placed in a precise-positioning mode 
when the content of the bit 51a or 51b is "1", and judges that the 
printing device is in a normal-positioning mode when the content of the 
bit 51a, 51b is "0". Thus, the CPU 35 serves as judging means for checking 
if the printing device is currently placed in the precise-positioning mode 
or in the normal-positioning mode. 
The ROM 53 stores programs for controlling the driver circuits 37, 39, 41, 
43, 45. The following programs are similar to those used in a known 
serial-impact printer: program for operating the wheel drive motor 27 for 
indexing the type wheel 19 to bring the selected type element 25 into the 
predetermined printing position in front of the print hammer 29; program 
for operating the paper feed motor 7 to rotate the platen 1 in the 
clockwise and counterclockwise directions for feeding the sheet of paper 
5; program for operating the ribbon feed motor 33 to feed the ribbon 31 
past the selected type element 25; and program for driving the print 
hammer 29 to impact the selected type element 25 against the sheet of 
paper 5. 
Referring next to FIG. 4, the operation of the printing device constructed 
as described hitherto will be described. For easy understanding, steps of 
operation are indicated by step numbers following letter S. 
Initially, the PRINTER/TYPEWRITER selector key 49d is set by the operator 
to select the PRINTER mode or TYPEWRITER mode. The MODE data 
representative of the currently selected mode is stored at the bit 51b in 
the RAM 51. The CPU 35 reads out the MODE data in step S1. In the case 
where the TYPEWRITER mode is selected, for example, the content "0" of the 
bit 51b is read out by the CPU 35. Based on the MODE data "0", the CPU 35 
checks in step S2 whether the TYPEWRITER mode or the PRINTER mode is 
selected. If the MODE data is "0" and the TYPEWRITER mode is selected, the 
CPU 35 judges that the carriage 13 should be positioned with relatively 
high accuracy, and goes to step S3 to move the carriage 13 at a 
comparatively low speed. More specifically, step S3 is executed wherein 
low-frequency drive pulses are applied to the motor driver circuit 39 
until the carriage 13 is moved to the commanded printing position. As a 
result, the carriage drive stepper motor 15 is operated to move the 
carriage 13 at the comparatively low rate, and is stopped so that the 
carriage 13 is positioned at the commanded position. The CPU 35 judges 
that the movement of the carriage 13 is stopped when the last drive pulse 
is applied to the driver circuit 39. 
A curve C2 of FIG. 5 indicates the movement of the carriage 13 in relation 
to time, when the carriage 13 is moved in step S3 in the TYPEWRITER mode 
(i.e., at a comparatively low rate). As shown in the figure, the carriage 
13 undergoes a transient vibrational movement when the carriage movement 
is stopped at the predetermined or commanded position "b", at a point of 
time "t0'". 
Then, the CPU 35 goes to step S4 to read out the SPECIAL-PRINTING data 
stored at the bit 51a in the RAM 51, and then to step S5 wherein the CPU 
35 checks if any one of the BOLDFACE, SHADOW and VERTICAL SCORE keys 49a, 
49b, 49c has been operated. This checking in step S5 is executed for 
determining whether a SPECIAL-PRINTING mode is established with the key 
49a, 49b, 49c set in the ON position. If the SPECIAL-PRINTING mode is 
established, step S6 is performed to allow a comparatively long waiting 
time between the end of movement of the carriage 13 in step S3, and the 
start of activation of the print hammer 29 to impact the selected type 
element 25 in step S7 which will be described. Namely, if the BOLDFACE, 
SHADOW or VERTICAL SCORE key 49a, 49b, 49c has been depressed and the 
SPECIAL-PRINTING data "1" is stored at the bit 51a, the CPU 35 judges in 
step S5 that the printing device is placed in the SPECIAL-PRINTING mode. 
In this case, the CPU 35 goes to step S6 to allow a comparatively long 
time before the type element 25 is impacted, so that the amount of the 
transient vibrational movement of the carriage 13 is sufficiently reduced 
and the carriage 13 is positioned accurately at the commanded position 
"b". After the elapse of the predetermined comparatively long waiting time 
(between points "t0'" and "t4" of the curve C2 in FIG. 5), the CPU 35 goes 
to step S7 to apply a drive signal to the hammer driver circuit 45 to 
activate the print hammer 29, whereby the selected type element 25 of the 
type wheel 19 is impacted against the sheet of paper 5 via the ribbon 31 
interposed between the type element 25 and the paper 5. Thus, the 
boldfaced or shadow printing or vertical scoring is started only after the 
carriage 13 and the type element 25 have been accurately positioned. 
In the case where none of the keys 49a, 49b, 49c have been depressed and 
the SPECIAL-PRINTING data "0" is stored at the bit 51a of the RAM 51, the 
CPU 35 judges in step S5 that the SPECIAL-PRINTING mode is not 
established, and therefore goes to step S8 in which comparatively short 
waiting time is given before the print hammer 29 is activated in step S7. 
It is noted that the printing of characters in the normal printing mode 
does not require so high positioning accuracy of the carriage 13 as is 
required in the SPECIAL-PRINTING mode. Upon expiration of the 
predetermined comparatively short waiting time, the drive signal is 
applied in step S7 to the hammer driver circuit 45 to activate the print 
hammer 29. The type element 25 is impacted by the print hammer 29 at a 
point of time "t2" of the curve C2 in FIG. 5. In this case, the amount of 
deviation of the actual printing position from the predetermined position 
"b" due to the transient phenomenon of the carriage 13 is held within a 
permissible positioning tolerance l2. With the positioning deviation or 
error held within this range l2, the printed character may be corrected 
satisfactorily, that is, an erroneously entered character may be well 
erased and a desired character may be printed. Thus, the positioning error 
of the carriage 13 within the tolerance l2 will not result in degrading 
the printing quality to such extent that gives an unpleasant impression to 
the reader. Thus, the waiting time between "t0'" and "t2" in the normal 
printing mode is considerably shorter than the waiting time between "t0'" 
and "t4" in the SPECIAL-PRINTING mode, whereby the printing speed is 
accordingly increased. 
Referring back to step S1, if the PRINTER mode is selected by the selector 
key 49d and the MODE data "1" is stored at the bit 51b in the RAM 51, the 
CPU 35 judges in step S2 that the PRINTER mode is selected. In this case, 
the CPU 35 goes to step S9 wherein high-frequency drive pulses are applied 
to the motor driver circuit 39 to operate the carriage drive motor 15 for 
moving the carriage 13 at a comparatively high speed, as indicated by a 
curve C1 in FIG. 5. In this connection, it is noted that the PRINTER mode 
of operation, which does not permit correction of printed characters, does 
not require so high positioning accuracy of the carriage 13 as is required 
in the TYPEWRITER mode. 
Subsequently, the CPU 35 goes to step S10 similar to step S4, to read out 
the SPECIAL-PRINTING data at the bit 51a, and to step S11 similar to step 
S5, to check if the SPECIAL-PRINTING mode is established or not. If any 
one of the keys 49a, 49b, 49c has been operated and the SPECIAL-PRINTING 
data "1" is read out, the CPU 35 judges in step S11 that the 
SPECIAL-PRINTING mode is established. In this instance, the CPU 35 
executes step S12 to give a comparatively long waiting time before the 
following step S13 is executed to activate the print hammer 29. 
As soon as the predetermined comparatively long waiting time (between "t0" 
and "t3" of FIG. 5) has elapsed, the drive signal is applied to the hammer 
driver circuit 45 to activate the print hammer 29 and thereby impact the 
selected type element 25 against the paper 5. In this case, the amount of 
deviation of the actual printing position from the predetermined position 
"b" due to the transient phenomenon of the carriage 13 is held within a 
permissible positioning tolerance l3. With the positioning deviation or 
error held within this range l3, the printing in the SPECIAL-PRINTING mode 
may be accomplished with satisfactory printing quality. Namely, the 
positioning error of the carriage 13 within the tolerance l3 will not 
result in degrading the quality of the boldfaced or shadow printing or 
vertical scoring, to such extent that gives an unpleasant impression to 
the reader. The waiting time between "t0" and "t3" in the SPECIAL-PRINTING 
mode in the PRINTER mode is considerably shorter than the waiting time 
between "t0" and "t4" given in the conventional printer. Hence, the 
printing speed is accordingly increased. 
If none of the keys 49a, 49b, 49c have been operated and the 
SPECIAL-PRINTING data "0" is read out in step S10, the CPU 35 judges that 
the SPECIAL-PRINTING mode is not established, and goes to step S14 to 
allow a comparatively short waiting time between "t0" and "t1" of the 
curve C1 of FIG. 5. That is, the drive signal is applied in step S13 to 
the hammer driver circuit 45 at point of time "t1" shortly after the 
carriage 13 has reached the predetermined position "b". 
In this case, the amount of deviation of the actual printing position from 
the predetermined position "b" due to the transient phenomenon of the 
carriage 13 is held within a permissible positioning tolerance l1. With 
the positioning error held within this range l1, the normal printing in 
the PRINTER mode may be accomplished with satisfactory printing quality. 
Namely, the positioning error of the carriage 13 within the tolerance l1 
will not result in degrading the printing quality to such extent that 
gives an unpleasant impression to the reader. Furthermore, the speed of 
the normal printing in the PRINTER mode is very much increased, since the 
activation of the print hammer 29 is effected at point "t1". 
As discussed hitherto, the CPU 35 serves as judging means for checking if 
the printing device is placed in the PRINTER mode or in the TYPEWRITER 
mode, and for checking if the SPECIAL-PRINTING mode is established or not. 
These checking operations are carried out by reading the MODE and 
SPECIAL-PRINTING data stored in the RAM 51. In addition, the CPU 35 serves 
as switching means for selecting a comparatively low or high rate of 
movement of the carriage 13, based on whether the PRINTER or TYPEWRITER 
mode is selected. Further, the CPU 35 serves as switching means for 
selecting a comparatively long or short waiting time between the end of 
movement of the carriage 13 and the start of activation of the print 
hammer 29, based on whether the SPECIAL-PRINTING mode is established or 
not. In the TYPEWRITER mode and the SPECIAL-PRINTING mode, the carriage 13 
should be positioned at the predetermined printing positions with 
relatively high accuracy, and therefore the carriage 13 is moved at a 
comparatively low speed and the print hammer 29 is activated a 
comparatively long length of time after the carriage 13 has been moved to 
the predetermined position. In the PRINTER mode, a permissible range of 
positioning error of the carriage 13 is relatively wide, and therefore the 
carriage 13 is moved at a comparatively high speed and the print hammer 13 
is activated a comparatively short length of time after the end of 
movement of the carriage 13. Consequently, the overall printing speed of 
the printing device is increased, without lowering the printing quality 
even when the printed characters are corrected in the TYPEWRITER mode, or 
even when the special printing such as boldfaced or shadow printing or 
vertical scoring is effected. 
While the present invention has been illustrated in its preferred 
embodiment, it is to be understood that the invention is not confined to 
the precise disclosure contained herein, but may be otherwise embodied 
with various changes which may occur to those skilled in the art. 
In the illustrated embodiment, an open-loop control is employed for 
controlling the carriage drive stepper motor 15, and the CPU 35 judges 
that the movement of the carriage 13 is stepped at the time the last drive 
pulse is applied to the driver circuit 39. If a closed-loop control is 
used, however, the amplitude of the transient vibrational movement of the 
carriage 13 is reduced. Under some printing conditions (modes), therefore, 
it is possible to start the activation of the print hammer 29 immediately 
after the carriage 13 has been moved to the predetermined printing 
position. Namely, the comparatively short waiting time (between "t0'" and 
"t2", or "t0" and "t1" of FIG. 5) used in step S8 or S14 in the 
illustrated embodiment may be further reduced, so that the print hammer 29 
is activated as soon as the carriage 13 has been moved to the 
predetermined position "b", if the closed-loop control is employed for the 
carriage drive stepper motor 15. 
Although the rate of movement of the carriage 13 is selected based on 
whether the TYPEWRITER or PRINTER mode is selected, while the waiting time 
of the print hammer 29 is selected based on whether the SPECIAL-PRINTING 
mode is established or not, it is possible that the movement rate of the 
carriage 13 be selected depending upon the specific type of printing 
(normal printing, or special printing such as boldface or shadow 
printing), while the waiting time of the print hammer 29 be selected 
depending upon the currently selected mode of printing (typewriter mode or 
printer mode). 
It will be obvious that other changes, modifications and improvements may 
be made in the invention without departing from the scope of the invention 
defined in the appended claims.