JPS6190222A - Constant current control device - Google Patents

Abstract

PURPOSE:To prevent the deviation of rise-up time of load current and to regularize the total energy supplied to the load, by correcting such as to increase the load current when the power source voltage is reduced and to reduce the load current when the power source voltage is increased. CONSTITUTION:When power source voltages VDD, VEE decreases, a current Ip supplied to a resistor 21 of a correction means 54 is also reduced, and an output voltage Vh of an operation amplifier 13 is lowered. Consequently, correction current Ib decreases resulting in the reduction of detection current Ip. As the result, a differential amplifying circuit 51 is activated so that the output voltage Vc of the operation amplifier 11 may increase, and load current Io is increased. Contrarily, when the voltages VDD, VEE increases, the current Ip and Ib also increase, and the detection current Ip increases. Therefore, the circuit 51 is activated to reduce the voltage Vc of the amplifier 11, and the current Io is reduced. Thus, the current Io is corrected and the deviation of the rise time of the current is prevented, and the total energy supplied to the load is maintained at a constant level.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a constant current control device, specifically a constant current control device that prevents fluctuations in current value due to fluctuations in power supply voltage, and is particularly applicable to printers, electronic typewriters, etc. -It can be applied to motor drive circuits, hammer drive circuits, magnet drive circuits, etc.

(Prior Art) Generally, constant current control devices are required to stably supply a target current value to a load.

Therefore, the current value of the load current is conventionally detected and controlled to a target current value by feedback control.

As such a conventional constant current control device, there is, for example, one shown in FIG.

In this constant current control device, when both transistors Tri and Tr2 are on, a load current of 1
1, the current supply time is controlled by the drive signal S1 input to the base terminal of the transistor Tri, and the control signal S2 is input to the base terminal of the transistor Tr2.
The current value of the load current 11 is controlled by. That is, the load current 1 is detected by the differential amplifier circuit 1 as a voltage drop across the current value detection resistor R1 connected in series with the coil L1, and is compared with a reference current by the arithmetic circuit 2 to generate the control signal S2.
is input to the transistor Tr2. The differential amplifier circuit 1 includes resistors R2, R3, R4゜R5, R6 and an operational amplifier O.
It includes a PI, differentially amplifies the voltage drop (RIXII) across the resistor R1, converts it into a current value through the resistor R6, and outputs the current value to the arithmetic circuit 2.

The arithmetic circuit 2 includes resistors R7, R8, R9, RIO, an operational amplifier OP2, and a reference voltage generator 3, and combines the detected current detected by the differential amplifier circuit 1 with the output voltage of the reference voltage generator 3 and resistors R9, R10. A control signal S2 is output by comparing it with a reference current determined by .

The control signal S2 has a negative value when the detected current is smaller than the reference current, and has a positive value when the detected current is larger than the reference current. A positive power supply voltage VOO is applied to the emitter terminal of the transistor T r 2,
A negative power supply voltage vl is applied to the emitter terminal of the transistor T r l.

Therefore, when the drive signal S10 is positive, the transistor T
During the period when rl is in the on state, transistor Tr2 supplies load current ■1 to coil L1 according to the value of control signal S2, and load current ■1 is controlled to a target current value.

However, in such a conventional constant current control device, when the voltage of the load power supply that supplies the load current fluctuates, the rise time of the load current fluctuates, and the total amount of energy supplied to the load fluctuates.

Therefore, if such conventional constant current control devices are applied to motor drive circuits, hammer drive circuits, magnet drive circuits, etc. of printers and electronic typewriters, normal control will be impossible due to motor tax adjustment, and A decrease in the attraction force of the magnet may cause uneven printing pressure or malfunction of the magnet.

In addition, in order to solve the same problem as above due to variations in power supply voltage, it is necessary to use high-precision parts in the power supply and to adjust the output voltage after the power supply is assembled. Preventive measures will increase costs due to increased parts costs and man-hours.

(Purpose of the Invention) Therefore, the present invention corrects the load current by increasing the load current when the power supply voltage decreases and decreasing the load current when the power supply voltage rises. The purpose is to prevent fluctuations in the rise time of the power supply and to keep the total amount of energy supplied to the load constant.

(Structure of the Invention) In order to achieve the above object, the present invention includes a switch means that turns on and off the load current supplied from the power supply to the load according to a control signal, and a load current that is caused by voltage drop of a resistor connected in series with the load. A constant current control device comprising: a differential amplifier circuit that detects and supplies a detected current; and a comparison arithmetic circuit that compares the detected current with a predetermined reference current and outputs the control signal. One feature of the present invention is that a correction means is provided for detecting fluctuations in the power supply voltage and adding a correction current corresponding to the fluctuations in the power supply voltage to the detected current.

Hereinafter, the present invention will be specifically explained based on examples.

1 to 6 are diagrams showing one embodiment of the present invention, and this embodiment is applied to a hammer drive device of a daisy printer. FIG. 1 is an overall perspective view of the daisy printer. In FIG. 1, reference numeral 11 is a die-cast frame, and a guide strip 12 of this frame 11 and a guide shaft 13 fixed to the frame 11 are connected to a carrier 1.
4 is attached so as to be able to reciprocate. This carrier 1
A carriage 16 to which a petal-shaped type wheel 15 is detachably attached is attached to the frame 4, and a platen 17 is provided in the center of the frame 11 along the reciprocating direction of the carrier 14.

As shown in FIG. 2, the carriage 16 is made up of a die-cast main body 18 in which various parts are assembled and implanted.

That is, a motor 19 is attached to the lower central portion of the main body 18, and a drive shaft 20, which is connected to the motor 19 via a universal joint (not shown), rotates at one end around a shaft 21, as shown in FIG. Arm 22 held freely
It is maintained by

The type wheel 15 is attached to the tip of the drive shaft 20, a magnetic body is provided in the middle of the arm 22, and magnets 23 and 24 are disposed on both sides of the arm 22 in the vertical direction. Each of the magnets 23 and 24 has a yoke made of laminated iron plates and silicon steel plates, and a solenoid is wound around this yoke. The magnet 23, 24 whose solenoid is energized attracts the arm 22 and shifts the type wheel 15 in the vertical direction. This type wheel 1
5 is regulated by a stopper (not shown). In addition, the main body 1 is attached to the tip of the arm 22 with a screw 25.
A leaf spring 26 fixed to 8 is attached.

Further, in FIG. 2, a holder 28 in which a hammer 27 is slidably housed is provided above the front part of the main body 18, and the hammer 27 is always urged rearward by a spring provided in the holder 28. ing.

A free end of an armature 29 supported rotatably is located behind the holder 28.
A rear end of a hammer 27 is linked to the free end of the hammer 9.

The armature 29 is attracted by the magnet 30 and rotates, causing the hammer 27 to protrude toward the tip to perform printing. When the coil wound around the yoke is energized, the magnet 30 attracts the armature 29, and the rotation of the armature 29 is restricted by stoppers 31 and 32.

On the top surface of the main body 18 is a ribbon cartridge 3 shown in FIG.
3 is set, and this ribbon cartridge 33 is held by a holding member 34 rotatably supported by the main body 18, and its front portion is shifted up and down by a push-up lever 35 shown in FIG. The ribbon cartridge 33 is vertically shifted 9 in conjunction with the vertical shift of the type wheel 15, but the vertical shift of the ribbon cartridge 33 is regulated by an upper stopper 36. The only parts that move when the ribbon cartridge 33 is shifted are the ribbon cartridge 33 itself and the holding member 34, so the movable weight is extremely light and vibrations are less likely to occur.

Each operation of this daisy printer, that is, selection operation, space operation, line feed operation, etc., is controlled by a control board unit 41 shown in FIG.
is equipped with a main control board 42 and a power board 43. The main control board 42 includes a circuit for controlling an interface circuit and a power board circuit, and the power board 43 includes a board for controlling a motor and a magnet, and a sensor board for amplifying feedback signals from the motor. . The hammer 27 is driven by a drive circuit on a hammer drive board 44, and the ribbon cartridge 33 and type wheel 15 are shifted by drive circuits on a ribbon lift drive board 45 and a shift drive board 46, respectively. Further, to move the carriage 16 by the printing interval, the space servo motor is driven by the drive circuit of the space servo drive board 47, and for line driving, the line feed motor is driven by the drive circuit of the line feed drive board 48. This is done by rotating the platen. Further, the selection servo motor is feedback-controlled by the drive circuit of the selection servo drive board 49 to rotate the type wheel 15, and the ribbon feed drive board 5
The ribbon in the ribbon cartridge 33 is fed by the drive circuit 0.

As the drive circuit of the hammer drive board 44, as shown in FIG. 6, a constant current control circuit is used. In FIG. 6, L2 is a coil as a load wound around the yoke of the magnet 30 for driving the hammer, and the coil L2
A resistor Rs for detecting load current is connected in series with the resistor Rs. The resistor Rs has a transistor T that controls the drive time.
r3 is connected, and a negative power supply VEE is applied to the emitter terminal of the transistor Tr3. A hammer signal HAM for instructing the drive of the hammer 27 is input from the drive circuit of the hammer drive board 44 to the base terminal of the transistor Tr3, and the transistor Tr3 is turned on when the hammer signal RAM has a positive value. Become. On the other hand, the collector terminal of a transistor Tr4 is connected to the coil L2, and a positive power supply voltage VDD is applied to the emitter terminal of the transistor Tr4, and a control signal C8, which will be described later, is input to its base terminal. The transistor Tr4 is in an off state when the control signal C8 has a positive value, and is in an on state when the control signal C8 has a negative value, and the load current 1o is supplied from the power supply to the load.
It acts as a switch means to turn on and off according to the control signal C8.

The load current Io supplied to the coil L2 is the differential amplifier circuit 5.
1 is detected. That is, the differential amplifier circuit 51 is composed of resistors R11, R12, R13, R14, R15 and an operational amplifier OpH, and the voltage drop across the resistor Rs (Rs・
Io) is differentially amplified (Vc) and converted into a current value by a resistor R15 to supply a detection current Ia. This detected current Ia is compared with a predetermined reference current by a comparison calculation circuit 52. The comparison calculation circuit 52 includes resistors R16, R17, and R1.
8, R19, an operational amplifier 0P12, and a reference voltage generator 53. The operational amplifier ○P12 receives the detection voltage Vd from the detection current Ia at its non-inverting input terminal, and the reference voltage generator 53 at its inverting input terminal. A comparison voltage Vf obtained by dividing the output voltage Ve of 1 by resistors R18 and R19 is input. That is, the comparison calculation circuit 52 compares the detected current a with the output voltage Ve of the reference voltage generator 53 and the resistor R18.
, R19 and the control signal C8.
The control signal C8 is output when the detected current a is smaller than the reference current (Vd<Vf).

It is a negative value, and when the detection current Ia is larger than the base i4g current (Vd>Vf), it is a positive value. Therefore, the comparison calculation circuit 52 outputs the control signal C8 so that Vd=Vf, thereby controlling the load current IO to the target current value.

In FIG. 6, 54 is a correction means for correcting fluctuations in the power supply voltages V, . Resistance R22, R23, R24, R25
, R26. The correction means 54 is a resistor R20
, resistance R21 due to the fluctuation detection current Ip flowing through R21.
The voltage drop (R21 Output. That is,
The correction current Ib is added to the detection current Ia, and is added to the output voltage Ve of the reference voltage generator 53 and the resistors R18 and R1.
By appropriately setting 9 and determining the reference current, it is possible to control the load current 0 to a target current value.

In addition, in FIG. 6, Dl is a flywheel diode of the coil L2.

Next, the action will be explained.

When the recording paper is set, the carriage 16 is moved to a predetermined position, and the printing type is selected by rotating the type wheel 15, the hammer signal RAM input from the main control board 42 to the transistor Tr3 of the hammer drive board 44 is output. switches from negative to positive.

At this time, since the detection current Ia is zero, the control signal C8
is positive, and the transistor Tr4 is in the on state. Therefore, when the hammer signal RAM switches from negative to positive, the transistor Tr3 turns on and the coil L2
The load current IO begins to flow, and the magnet 30 begins to attract the armature 29. When the load current IO increases and the detection current Ia becomes larger than the reference current, the control signal C8 switches from negative to positive, the transistor Tr4 turns off, and the supply of the load current Io from the power supply is cut off.

At this time, the load current IO flowing through the coil L2 circulates through the resistor Rs, the diode D1, and the coil L2, and is attenuated. Thereafter, when the detected current Ia decreases with the decrease of the load current IO and becomes smaller than the reference current, the control signal C8 switches from positive to negative. Therefore, the transistor T r 4 is turned on again and the supply of the load current 0 to the coil L2 is resumed. This control operation of the load current 0 is performed during the period when the hammer signal RAM is positive, and the load current Io is controlled to the target current value. Hammer signal RA
The time during which M is positive is shorter than the time until the armature 29 collides with the stopper 32. Therefore, hammer 2
The printing pressure according to 7 is determined by the total amount of energy supplied during the period when the hammer signal HAM is positive, and the control circuit of the main control board 42 adjusts the positive time of the hammer signal RAM depending on the type of printing type. The printing pressure is controlled to be constant by controlling the pressure.

Next, a case where the power supply voltage Vpp and VEE fluctuate will be explained.

Now, if the power supply voltage V,..., vat drops,
The current Ip flowing through the resistor R21 of the correction means 54 decreases,
The output voltage vh of the operational amplifier 0P13 decreases. Therefore, the correction current Ib decreases, causing the detection current rp to decrease. As a result, the differential amplifier circuit 51 operates as an operational amplifier 0PII.
operates to increase the output voltage Vc of the load current I
o increases. Therefore, the power supply voltage V. . ,v'EE
It is possible to correct the decrease in the load current IO due to the decrease in the load current IO, and it is possible to prevent the rise time of the load current IO from being delayed.

As a result, the total amount of energy supplied to the magnet 30 can be prevented from decreasing, and the printing pressure can be prevented from decreasing.

Conversely, when the power supply voltages VOa and VEE rise, the current Ip increases, the correction current Ib increases, and the detection current Ip increases.
increases. Therefore, the differential amplifier circuit 51 operates to reduce the output voltage VC of the operational amplifier 0PII,
Load current factor 0 decreases.

As a result, it is possible to correct the increase in load current Io due to the increase in power supply voltage VCIEI, ■εε. Therefore, an increase in the total amount of energy supplied to the magnet 30 can be prevented, and an increase in printing pressure can be prevented.

The above correction operation can be expressed as follows. That is, in the differential amplifier circuit 51, the operational amplifier 0PII
The output voltage Vc is expressed by the following equation.

-V a
a, R14/R13=b, then vc=upper two 'XVb+Io・Rs-b1+a...(2) Now, if a-b=1, the first term on the right side of equation (2) is It becomes zero.

V c ”I o-Rs-b -(
3).

Next, in the correction means 54, the output voltage vh of the operational amplifier 0P13 is similarly expressed by the following equation.

VE [:
If 2/R23=c and R25/R24=d, then v h
=-L knee 5Lx V k + I p-R21
・d1+c (5) Now, if c-d=1, the first term on the right side of equation (5) becomes zero, and V h = I p-R21-d
−・−・−(6).

Further, in the comparison calculation circuit 52, the comparison voltage Vf is expressed by the following equation.

veIIR1910,0, (7) vf=R18+R19 When the operational amplifier 0P12 is in a balanced state, the following equation holds true.

V e 'R19,,,,,, (8゜vd:■f:R
18+R19 Therefore, now let the current flowing through the resistor R17 be Ic, and the current flowing through the resistor R16 be Id.

Ic+Ib=Ia+Id-...(9)
V e V d + V h V d η宸V c
R17R26R15 +ヱ±niケ肚・・・(10) R16 Note that Vop is the output voltage of operational amplifier 0P12 (10)
Substituting equation (3) into the equation and rearranging the load current Io.

Furthermore, by substituting and rearranging equation (6), we get...
(12) Now, R22, R23, R24, R25) R20, R2
1, the current Ip is expressed by the following equation.

Engineering p# 叉eniki L ・・・・・・(13)
R20+R21 Substituting equation (13) into equation (12) and rearranging, I O
= X -ct (V hit - V want)
, (14) However.

becomes.

As is clear from equation (14), the equation for the load current factor 0 includes a term with a minus sign in which the absolute value of the power supply voltage vDf) and vfE are multiplied by the coefficient. Therefore, when the absolute values of the power supply voltages VDD and VEE decrease, the load current 0 is corrected to increase, and the power supply voltage vt10
, ■□ increases, the load current factor 0 is corrected to decrease. The rate of this correction is the coefficient α above
It can be set arbitrarily by appropriately selecting the setting value of . As a result, it is possible to prevent variations in the rise time of the load current 0 due to variations in the power supply voltages V and VEE, and it is possible to control the total amount of energy supplied to the coil L2, which is the load, to be constant at all times. Therefore, the printing pressure can always be controlled to a stable predetermined pressure.

Although the above embodiment describes the case where the present invention is applied to a hammer drive device of a daisy printer, the scope of application of the present invention is not limited to this, and is generally applicable to a constant current control device that controls a load current to a constant value. It can be applied, but
It is particularly useful as a constant current control device for the above-mentioned magnets, DC motors, pulse motors, and the like. In this case, malfunctions due to variations in the attraction force of the magnets can be prevented, and loss of control due to motor step-out can be prevented.

Further, although a power source with a positive potential is used as the power source, the present invention can be similarly applied to a power source where one side is at a positive potential and the other side is at a ground potential, or one side is at a ground potential and the other side is at a negative potential. .

(Effects) According to the present invention, in a constant current control device, fluctuations in load current due to fluctuations in power supply voltage can be corrected, so fluctuations in the rise time of load current can be prevented.
The total amount of energy supplied to the load can always be controlled to a predetermined value.

[Brief explanation of the drawing]

1 to 6 are diagrams showing an embodiment of the constant current control device of the present invention. FIG. 1 is a perspective view of a daisy printer to which an embodiment of the present invention is applied, and FIG. A top view of the carriage of the printer, FIG. 3 is a front view of the carriage of the daisy printer, and FIG. 4 is a perspective view of the ribbon cartridge used in the daisy printer.
FIG. 5 is a block diagram of the control board unit of the daisy printer, and FIG. 6 is a circuit diagram of the constant current control device of the present invention applied as the hammer drive device. FIG. 7 is a circuit diagram showing an example of a conventional constant current control device. 51...Differential amplifier circuit. 52... Comparison calculation circuit, 54... Correction means, L2... Coil (load), Tr4... Transistor, Rs... Resistor . R21...Resistance. Figure 3 2nd Figure 4

Claims (2)

[Claims] (1) A switch means that turns on and off the load current supplied from the power supply to the load according to a control signal, and a differential amplifier circuit that detects the load current based on the voltage drop of a resistor connected in series with the load and supplies the detected current. and a comparison calculation circuit that compares the detected current with a predetermined reference current and outputs the control signal.
1. A constant current control device comprising: a correction means for detecting fluctuations in the power supply voltage and adding a correction current corresponding to the fluctuations in the power supply voltage to the detected current. (2) Claims characterized in that the correction means detects fluctuations in power supply voltage based on fluctuations in voltage drop of a resistor connected to the power supply, and outputs a correction current corresponding to the fluctuations in the power supply voltage. The constant current control device according to item 1.