CRT display apparatus

A CRT display apparatus equipped with a control apparatus for performing a focusing control and a brightness control by changing a grid voltage by means of a potentiometer. The control apparatus includes a motor for driving the potentiometer in response to an externally supplied control signal, and the motor is mechanically arranged with the potentiometer in an integrated form. Both of a plurality of potentiometers and motors for driving the plural potentiometers are formed on the same substrate in an integrated form. Also, the control apparatus is molded with a flyback transformer for constituting the CRT display apparatus. The motor is constructed of either an ultrasonic motor, or a plastic geared motor.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a CRT display apparatus. More 
specifically, the present invention is directed to a CRT (cathode-ray 
tube) display apparatus having a high-voltage/precise voltage control 
apparatus for performing a focusing control and a brightness control 
(screen voltage control). 
In the conventional apparatuses for utilizing high-precision electron 
beams, such as CRT display apparatuses (involving television receivers), a 
focusing control is necessarily required by which a high voltage of a 
focusing electrode is controlled, or adjusted to realize a clear beam 
spot. Concretely speaking, in a computer color CRT display apparatus with 
employment of a bipotential tube, a high-voltage focusing control voltage 
is needed, and a variable voltage dividing circuit (constructed by a 
potentiometer) for dividing an anode voltage into relatively high voltages 
of 6 to 8 KV is employed to apply such relatively high voltages to two 
focusing electrodes in order to follow variations in the anode voltage at 
high speeds. Then, these voltages are controlled so as to minimize the 
spot diameters, while a parabolic voltage is applied via a capacitor to 
one of these focusing electrodes. Similarly, another voltage dividing 
circuit is used so as to follow the screen voltage. A typical conventional 
voltage controlling circuit has been opened in, for instance, 
JP-A-63-203063. 
That is to say, this prior art publication describes an improvement in the 
focusing control of the color CRT display apparatus. The voltage dividing 
resistor circuit is arranged by such a series circuit constructed of the 
parallel resistor circuit used to derive convergence voltages for the 
first and second convergence electrodes with the electrode pieces for 
constituting the 4-pole lense, and also the resistor circuit provided at 
the low voltage side. To this convergence-voltage deriving parallel 
resistor circuit, both of the variable resistor for controlling the first 
convergence voltage and the variable resistor for controlling the second 
convergence voltage are connected in a parallel form. These two variable 
resistors are independently adjusted or controlled, so that preselected 
optimum DC convergence voltages are applied to the first convergence 
electrode and the second convergence electrode, and furthermore, the 
parabolic voltages synchronized with the deflection period are applied to 
the first and second convergence electrodes. As a consequence, optimum 
convergence conditions of the electron beams can be obtained over not only 
the peripheral portion of the screen, but also the central portion 
thereof, and also the variable screen voltage for controlling the cut-off 
point can be obtained at the same time. 
Since this conventional focusing control operation requires very precise 
beam spot adjustments, resulting in fatigue of operators, it is preferable 
to automatically perform such a focusing control operation. However, it is 
practically difficult to realize an automatic focusing control operation, 
because the above-described focusing control operation must be carried out 
under high voltage and precise adjustment. 
As to the conventional high voltage/precise controlling method, such an 
automatic control method may be conceived that a motor-driven screw driver 
having a precise alignment servo mechanism is used to be fitted to the 
rotary unit of the above-described focus controlling potentiometer. 
However, such an automatic focus control method owns the following 
drawbacks. That is to say, it is rather difficult to maintain reliability 
over a long time for such a mechanically precise alignment. Moreover, this 
difficulty is emphasized because the recently developed CRT display 
apparatuses employ the tilt and swivel mechanism. Accordingly, no 
automatic control method with high precision and reliability have been 
developed in view of practical capability. 
SUMMARY OF THE INVENTION 
The present invention provides a compact control apparatus with high 
reliability, capable of automatically performing a high voltage and 
precise voltage control (adjustment) for a focusing control and a 
brightness control of a CRT display apparatus. 
The present invention realizes an automatic focusing control and a screen 
control with employment of the above-described control apparatus. 
The present invention also minimizes magnetic interference. 
The present invention a CRT (cathode-ray tube) display apparatus comprising 
a control apparatus for controlling a CRT display by changing a grid 
voltage by means of a potentiometer. The control apparatus includes a 
motor for driving the potentiometer in response to an externally supplied 
control signal, and the motor is mechanically arranged with the 
potentiometer in an integrated form. Also, to achieve this object there 
are provided the following technical ideas. A plurality of potentiometers 
and the motors for driving these potentiometers are formed on the same 
board in an integrated form. The control apparatus is molded with a 
flyback transformer for constituting the CRT display apparatus. Also, the 
above-described motor is constructed of either an ultrasonic motor, or a 
plastic geared motor. 
The present invention provides an image apparatus positioned at a display 
screen side of the CRT display apparatus, and the motor is driven in 
response to an output signal derived from the imaging apparatus to 
automatically control at least one of focusing and brightness of the CRT 
display apparatus. 
The present invention provides the drive motor adjacent to the flyback 
transformer, whereby the control apparatus can be operated without any 
trouble even in a strong magnetic field. 
In accordance with the means for achieving the above-described objects of 
the present invention, since the potentiometer for dividing the high 
voltage is mechanically combined with the motor for driving this 
potentiometer in an integrated form, a compact automatic control apparatus 
can be realized. Also, since a plurality of potentiometers and the motor 
for driving these potentiometers are formed on the same board in an 
integrated form, which are then molded with the flyback transformer in an 
integrated form, the CRT display apparatus can be made compact. Even when 
such a drive motor as an ultrasonic motor and a plastic geared motor is 
integrally molded with the flyback transformer, or is operated adjacent to 
the flyback transformer, this drive motor can be operated even in the 
strong magnetic field, so that magnetic interference can be minimized and 
reliability can be improved. Also, since the ultrasonic motor or the 
plastic geared motor may be driven by intermittently applying a pulse 
voltage thereto, the potentiometers may be driven in a stepwise mode, so 
that a fine and precise voltage control is realized. 
In accordance with a means for achieving another object of the present 
invention, the motor formed with the potentiometers in an integrated form 
is driven based upon the output signal derived from the imaging apparatus 
arranged at the display screen side of the CRT display apparatus in order 
that both of the focusing and the brightness of the CRT apparatus becomes 
optimum, whereby an automatic focusing/brightness controlling operation 
can be realized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, there is shown a focusing voltage control (adjustment) and a 
screen voltage control (adjustment) of a CRT (cathode-ray tube) display 
apparatus, to which the present invention has been applied, according to a 
preferred embodiment of the present invention. In FIG. 1, a high voltage 
generating circuit 100 is constructed of a flyback transformer 110, an 
output voltage dividing circuit 120, and other circuit elements, and is 
resin-molded in an integrated form except for a terminal thereof in order 
not to expose the high voltage unit. A primary winding 131 of the flyback 
transformer 110 is connected via a resistor 512 in parallel to a 
horizontal deflection coil 511, and is driven (energized) by a +B power 
supply applied to a terminal 513 and a horizontal deflection drive circuit 
300. More specifically, the flyback transformer 110 is driven via the 
primary winding 131 by a pulse voltage generated during the horizontal 
flyback period of the horizontal synchronization (deflection) pulse 
voltage. It should be noted that the horizontal synchronization pulse is 
input to a terminal 310. 
On the other hand, an output of secondary windings 132 and 133 of the 
flyback transformer 110 are applied as an anode voltage of a CRT display 
apparatus 200 in such a manner that this output voltage is rectified by 
rectifier diodes 136 and 137, and then smoothened by a capacitor 138, and 
thereafter applied via a high voltage output terminal 153. A typical 
voltage range of this anode voltage is 25 KV to 30 KV. Another terminal of 
the secondary winding 133 of the flyback transformer 110 is grounded 
through an over current detecting circuit 520 arranged by a parallel 
circuit of a capacitor 526 and a resistor 527. 
It is so arranged that the anode output voltage of the flyback transformer 
110 is detected via a voltage dividing circuit constructed of resistors 
having high resistance values 141 and 142, and the pulse voltage of the 
horizontal deflection drive circuit is controlled via a high voltage 
control circuit 400 in order that the anode voltage becomes a preselected 
constant voltage. 
The high voltage to be applied to an anode output terminal 153 is divided 
by an automatic controlling apparatus 120 arranged by a resistor having a 
high resistance value 143, potentiometers with high resistance values 121a 
and 121b, and drive motors 111a and 111b. A divided voltage is applied 
from a terminal 154 to a focusing electrode of the CRT display apparatus 
200 (normally, although a high-precision CRT display apparatus, or a 
large-screen television owns two focusing electrodes, only one focusing 
electrode is shown for purposes of simple illustration in the preferred 
embodiment of FIG. 1). Similarly, the divided voltage is applied from a 
terminal 155 to a screen electrode of the CRT display apparatus 200. 
Normally, voltage ranges of these required divided voltages are 6 to 8 KV 
for the focusing electrode and 500 to 800 V for the screen electrode. 
A resistance value of the potentiometer 121a for controlling the focusing 
voltage is selected to be several to 10M (ohms). Both of the potentiometer 
121a and a drive motor 111a are mechanically formed in an integral mode, 
and either a compact plastic geared motor, or an ultrasonic motor is 
employed as this drive motor. This compact motor owns such a feature that 
relatively no magnetic influence is given and this motor is suitable to be 
molded in an integrated form with the flyback transformer 110. 
An industrial imaging apparatus (ITV) 600 equipped with an optical 
enlarging lens system and a light receiving sensor is arranged at a screen 
side of the CRT display apparatus 200, the output 610 of which is 
connected to a controller 700 including a microcomputer. Drive outputs of 
the controller 700 are connected to an input line 116'a of the drive motor 
111a for controlling the focusing voltage and to an input line 116b of the 
drive motor 111b for controlling the screen voltage, respectively. 
In the above-described circuit arrangement shown in FIG. 1, upon receipt of 
the synchronization at the synchronization input terminal 310, the 
horizontal deflection drive circuit 300 drives the deflection coil 511 and 
the primary winding coil 131 of the flyback transformer 110 to generate a 
voltage having a value on the order of 30 KV at the anode output terminal 
153 of the secondary winding of the flyback transformer 110. This anode 
voltage is detected by the voltage dividing circuit constructed of the 
registers having the high resistance values 141 and 142, and the divided 
anode voltage is negative-feedback-controlled by the high voltage control 
circuit 400 so as to obtain a constant voltage, so that this anode high 
voltage becomes constant, and the CRT display apparatus 200 is under 
display condition. 
Under such a condition, the automatic focusing control (adjustment) of the 
arrangement shown in FIG. 1 is performed as follows: 
It should be noted that FIG. 2 shows an example of a crosshatch pattern 
employed in the automatic focusing control of the arrangement shown in 
FIG. 1, and FIG. 3 shows a waveform of an electric output signal 
corresponding to a line width of the crosshatch pattern used in the 
automatic focusing control of the arrangement shown in FIG. 1. 
First, crosshatch patterns (cross-shaped patterns) 211 to 214 as 
represented in FIG. 2 are projected onto positions on the screen of the 
CRT display apparatus, where the focusing should be controlled. These 
crosshatch patterns are focused by the imaging apparatus 600 to convert 
the line components of the crosshatch patterns into electrical signals as 
shown in FIG. 3. That is to say, the waveform of FIG. 3 corresponds to the 
electric signal output obtained when the line component of the crosshatch 
patterns are scanned by the imaging apparatus (ITV) 600. In this case, the 
line width is defined by a scanning time duration "t.sub.w " at an 
amplitude of A/2. In other words, a value "W" obtained by counting this 
time duration "t.sub.w " by a counter with a constant clock is used as 
focusing information, and the focusing voltage is controlled in order that 
this value "W" becomes minimum. Such a condition is regarded as a best 
focusing condition. 
A control and a judgement for this focusing control operation are executed 
by the controller 700 equipped with the microcomputer shown in FIG. 1. 
That is, in FIG. 1, from the output 710 of the controller 700, a stepwise 
drive voltage is applied to the drive motor 111a of the automatic 
controlling apparatus 120, whereby the dividing voltage of the focusing 
potentiometer 121a is fine-controlled in such a manner that the signal 
"t.sub.w " of the above-described line width becomes minimum. 
In FIG. 4, there is shown a flow chart for explaining the above-explained 
automatic focusing control operation. A major point of this automatic 
focusing control operation will now be summarized. After the sensor of the 
imaging apparatus has been focused onto an object for control (at a step 
2), a line width "Wi" sensed at this time is stored as an initial value 
into a register of the microcomputer (step 3). Subsequently, the drive 
voltage is stepwise increased by 1 step under which a line width 
"W.sub.i+1 " is sensed (step 4), and then a judgement is made of a step 
direction based upon a relative relationship between the first-sensed line 
width "Wi" and the second-sensed line width "W.sub.i+1 ". Thereafter, the 
drive voltage is stepwise produced along this judged stepping direction. 
If the judgement result would be reversed, then the drive voltage is 
returned to that for the previous step by 1 step, so that the fine control 
is completed. 
It should be noted that as to the screen voltage control, brightness of the 
screen is measured by the ITV 600 and then the screen control 
potentiometer 121b is driven in such a way that the measured brightness of 
the screen becomes predetermined brightness in a similar manner to that of 
the above-explained automatic focusing control. 
With respect to the arrangement for the automatic focusing voltage (and 
screen voltage) control system as indicated in FIG. 1, both of the 
adjustment (control) precision and the reliability of the automatic 
control apparatus 120 are very important, which are indicated by the 
function of the motor driven potentiometer. 
It should be noted that since the control precision about the focusing 
voltage and the screen voltage must be selected to be approximately 1% of 
the output voltage, a stepwise value for 1 step control may be preferably 
selected to be approximately 1/4 (0.25)%. Also, it is preferable that the 
automatic control apparatus 120 may be molded with the flyback transformer 
in an integrated form in view of reliabilities of the operations. As a 
consequence, the drive motor of the automatic control apparatus may 
preferably satisfy the below-mentioned conditions (1) to (3): 
(1). Even in a strong magnetic field, the drive motor of the automatic 
control apparatus is operable without any trouble. 
(2). Low heat dissipation during the normal motor drive operation. 
(3). The drive motor owns a stepwise characteristic and has large 
stationary torque. 
To satisfy the above-described conditions, either a plastic geared stepper 
motor, or an ultrasonic motor is employed as the drive motor in the 
preferred embodiment of the present invention. 
FIG. 5 schematically illustrates an example of a construction of an 
automatic control apparatus according to the present invention with 
employment of a plastic geared stepper motor as the drive motor. In the 
construction shown in FIG. 5, a high voltage potentiometer 121 is 
assembled with a stepper motor 111 having a plastic gear in an integrated 
form. The stepper motor 111 is driven via four drive signal lines 116 (in 
case of a four-pole stepper motor) by receiving a pulse signal produced 
from a motor drive control circuit 117 in response to a normal rotation 
input 118a and a reverse rotation input 118b. In this case, a gear down 
ratio of this plastic gear is selected to be approximately 0.25% as a 
voltage variation of the divided output voltage of the potentiometer for 
one step of the stepper motor, as previously explained. 
As a merit of employing such a speed-reduction purpose plastic gear of the 
drive motor, there are such that no adverse influence is given in the 
magnetic field and easy lubrication can be achieved. In addition, 
occurrences of excessive drive torque in an upper limit and a lower limit 
of the potentiometer can be suppressed since soft plastic such a Teflon 
(trademark) is used in a portion or a whole portion of the torque 
transmission, and a structure of the stopper can be made simple. 
FIG. 6 schematically shows a potentiometer employed in the automatic 
control apparatus, according to one preferred embodiment of the present 
invention. A resistor member having a thick film 125 is printed on a 
housing 121 of the potentiometer, and conductive terminals 122, 123 and 
124 are provided on both ends of this resistor member 125. A variable 
ring-shaped print conductive member 126 and a brush 127 form a wiper of 
the potentiometer. In case of the potentiometer shown in FIG. 6, the brush 
127 is made of a cylindrical metal spring coil, a half portion of which is 
embedded in a disk at the rotary member (not shown). This brush 127 can be 
firmly in contact with the resistor member 125 and the conductor 126 under 
a mechanically light load. 
FIG. 7 schematically indicates a sectional view of another automatic 
control apparatus, according to another preferred embodiment of the 
present invention, for containing an ultrasonic motor and a potentiometer 
in an integrated form. It should be noted that the same reference numerals 
shown in FIG. 5 are employed as those for denoting the same or similar 
components indicated in FIG. 6. In FIG. 7, a piezoelectric vibrating 
element is attached to a metal elastic member 113. Also, a rotary member 
115 is in contact with the above-described elastic member 113 via a 
friction member 114 attached thereto. The rotary member 115 is made of 
such an electric insulating member as a ceramics plate, in which a notch 
portion is partially formed. A half portion of the brush 127 made of a 
cylindrical metal spring coil for this potentiometer is embedded in this 
notch portion. This brush 127 is in contact with the thick-film resistor 
member 125 and the conductive member 126 of the potentiometer 121. 
Although not shown in FIG. 7, there are provided separating electrodes in 
the piezoelectric vibrating member 112, to which the voltage is applied, 
such an integrated form of the drive motor unit and the potentiometer unit 
are entered into a plastic housing (not shown) having a compression spring 
plate, and maintains a proper contact pressure. 
An operation of the automatic control apparatus with the above-described 
arrangement, shown in FIG. 7, will now be described. Two-phase AC voltages 
having a predetermined resonance frequency and 90.degree. different phases 
from each other are applied to the separating electrodes of the 
piezoelectric vibrating member driving unit 112. As a consequence, a 
traveling wave is produced in the piezoelectic vibrating member driving 
unit 112, and then amplified by the elastic member 113. Since the elastic 
member 113 is in contact with the rotary member 115 via the friction 
member 114 under exertion of pressure, the rotary member 115 receives a 
rotation force along a direction opposite to the traveling direction of 
the traveling wave, and therefore the rotary member 115 is rotated. As a 
result, the brush 127 of the potentiometer is also rotated so that the 
voltage applied to the potentiometer 121 can be controlled. Furthermore, 
the automatic control apparatus of FIG. 7 with employment of the 
ultrasonic drivemotor has such advantages, in addition to the 
above-described 3 conditions, as a high response characteristic, high 
resolution, a simple/compact construction, and a easy molding 
characteristic. 
It should be noted that a control circuit is required to correctly drive a 
plurality of automatic control apparatuses. 
FIG. 8 represents a control circuit for precisely driving three ultrasonic 
motors. In FIG. 8, a high frequency oscillator 511 of a servo motor 
control circuit 117 supplies a clock to a counter 512. The counter 512 
frequency-divides the inputted clock to obtain frequency-divided outputs 
having mutually different phases by 90.degree. from two output terminals 
531 and 532 thereof. It should be noted that the frequencies of the 
divided outputs are selected to be commonly the resonance frequency of the 
ultrasonic motor. Then, two divided output signals are inputted to 
exclusive OR gate circuits 513 and 514. The exclusive OR gate circuit 513 
has a phase inverting input terminal 535. In other words, the waveforms 
having 90.degree.-phases different from each other derived from the 
exclusive OR gate circuits 513 and 514 can invert the relationship between 
"lead" and "delay" in response to the conditions of the input signal of 
the terminal 535 by applying the input signal having 180.degree. different 
states of "1" or "0" to the terminal 535. These 2 phase output signals are 
supplied via AND gate circuits 515 and 516 each having an ON/OFF control 
terminal 536 to drive amplifiers (driver) 517 and 518, respectively. 
Outputs of the drive amplifiers 517 and 518 are supplied via filter 
reactors 521 and 522 and a multiplexer 525 to drive the respective 
ultrasonic motors 111a to 111c. 
The control circuit shown in FIG. 8 with the above-described circuit 
arrangement can select an arbitrary motor from three ultrasonic motors 
111a to 111c in response to the control input 526 of the multiplexer 525 
to control the normal rotation or the reverse rotation of the selected 
ultrasonic motor by the control terminal 535, and also can control the 
application time of the drive pulse by the control terminal 536. 
FIG. 9 is a sectional view of an automatic control apparatus according to a 
further preferred embodiment of the present invention. In the construction 
of FIG. 9, drive portions of an ultrasonic motor such as a piezoelectric 
vibrating member driving unit 112, a metal elastic member 113, and a 
friction member 114 are arranged at an outer circumference, and a main 
body 121 of potentiometer is positioned at a center portion of an inside, 
both of which are constructed by a common rotary member 115. With such a 
construction, since drive torque is produced at the outer peripheral 
portion to drive the load at the inner peripheral portion, there is a 
merit that the overall automatic control apparatus can be made thin and 
compact. 
FIG. 10 is a sectional view of an automatic control apparatus according to 
a further preferred embodiment of the present invention. In the 
construction of FIG. 10, a drive portion of an ultrasonic motor is 
identical to that of the preferred embodiment shown in FIG. 7, and there 
is such a different point that a shaft having a fitting concave for a 
screw driver is formed on a rotary member 115 of a potentiometer 
functioning as a load. With such a construction, the screw driver is 
fitted to the concave of the shaft 128, so that a manual control may be 
similarly performed. 
FIG. 11 represents an example in which the automatic control apparatus 
according to the present invention is assembled to the same board. In an 
application to a CRT using a plurality of voltage control circuits as 
shown in FIG. 1, it is preferable to form the automatic control apparatus 
as a circuit (assembling member) in which a plurality of elements have 
been assembled on the same board, in view of reliability about the mutual 
connections among the high voltage circuit elements, and also economical 
reasons. As a consequence, in the example of consequence, in the example 
of FIG. 11, a high-voltage dividing resistor member 143, two focusing 
control potentiometers 121a and a single screen voltage control 
potentiometer 121b of an automatic control apparatus 120 are mounted on a 
circuit board 121, which are mutually connected by a printed conductive 
member 129. Each of these potentiometers has a thick-film-printed resistor 
member 125 and a conductive member 126 contacting with a movable brush 
(not shown in detail). The movable brush of the respective potentiometers 
is driven by an ultrasonic motor (not shown) similar to that of FIG. 10 
which has been employed for each of the potentiometers. 
Since the automatic control apparatus according to the present invention 
has been constructed as illustrated in FIG. 11, reliability and economical 
matters about mutual connections among these components can be improved. 
Although there has been described in the above-explained automatic control 
apparatuses according to the preferred embodiments of the present 
invention that the ultrasonic motors and the potentiometers are of rotary 
type, these components may be alternatively constructed as a straight line 
motion type. 
In accordance with the present invention, since the potentiometers for 
dividing the high voltage and the motor for driving these potentiometers 
are mechanically formed in an integrated form in the CRT control 
apparatus, the CRT display apparatus can be made compact. Also, since a 
plurality of potentiometers and the motor for driving these potentiometers 
are formed on the same board in an integrated form, which are then molded 
with the flyback transformer in an integrated form, the CRT display 
apparatus can be made compact. Even when such a drive motor as an 
ultrasonic motor and a plastic geared motor is integrally molded with the 
flyback transformer, or is operated adjacent to the flyback transformer, 
this drive motor can be operated even in the strong magnetic field, so 
that magnetic interference can be minimized and reliability can be 
improved. Also, since the ultrasonic motor or the plastic geared motor may 
be driven by intermittently applying a pulse voltage thereto, the 
potentiometer may be driven in a stepwise mode, so that a fine and precise 
voltage control is realized. 
In accordance with another present invention, the motor formed with the 
potentiometers in an integrated form is driven based upon the output 
signal derived from the imaging apparatus arranged at the display screen 
side of the CRT display apparatus in order that both of the focusing and 
the brightness of the CRT apparatus become optimum, whereby an automatic 
focusing/brightness controlling operation can be realized.