JPS6321923B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a pulse energization duty ratio detection circuit,
The present invention relates to a pulse current type DC speed servo characterized by comprising a variable drive voltage supply circuit, a reference clock oscillator phase detection circuit, a switch type drive circuit, a DC motor, and an encoder.

With the development of print motors and coreless motors, these DC motors with low inertia rotors are now being used in control systems for printer carriages and the like.
For such control systems, particularly speed control systems, a phase lock loop control system as shown in FIG. 1 is generally used for the purpose of improving control accuracy and simplifying the control circuit.

A conventional example will be explained using FIGS. 1 and 2.

The device uses start command 1 as reference clock oscillator 2.
, the reference clock 3 is oscillated, the phase difference with the output pulse 5 of the encoder 11 is detected by the phase detection circuit 4, and the voltage (or current) of the power supply 8 is detected by the phase difference signal 6 by the switch type drive circuit. It is turned on and off at 7 and applied to the DC motor 10 as a pulsed energization signal 9.

To explain this operation process using FIG. 2, first, when a start command is applied at time 19, the detected phase difference signal 6 causes the reference clock period 13
A signal 9 corresponding to the phase difference is applied to the motor, and the speed 15 of the motor output shaft changes toward a set speed 14 determined by the frequency of the reference clock and the number of divisions of the encoder. The speed is 16 in the startup section until it reaches a constant value, and 1 in the steady speed section.
7. Changes like 18 in the stop section. In such a control system, a switch type drive circuit using four transistors as shown in FIG. 3 is used when the motor is used in both forward and reverse rotational directions. When rotating in the forward direction, the transistor 23,
When rotating 26 in the opposite direction, transistors 24 and 25
I am using it with it turned on. A control system using this switch-type drive circuit has the advantage that the circuit generates less heat than one using an analog circuit, and does not require a large-capacity power supply. However, because the drive voltage is always turned on and off at a constant rate, the motor generates a lot of noise, and the commutator of the motor is severely worn out due to sparks, etc.
This has the disadvantage that the life of the motor is significantly shortened. In particular, when trying to keep the start-up period 16 in a short time, such as in a printer's carriage movement control system, a relatively high-output motor is used.
3) becomes small, and this drawback becomes noticeable.

In order to eliminate such drawbacks, the present invention adds a duty ratio detection circuit 27 and a variable drive voltage circuit 28 as shown in FIG. The voltage applied to the motor is kept low by lowering the supply voltage of the motor. This operation will be explained using FIG. 5.

The device uses start command 1 as reference clock oscillator 2.
When the reference clock 3 is applied to the motor, the reference clock 3 is oscillated, and the phase detection circuit 4 detects the phase difference between the reference clock 3 and the output pulse 5 of the encoder 11 mounted coaxially with the motor. On the other hand, the duty ratio between this phase difference signal and the reference clock signal is detected by the duty ratio detection circuit 27, and when the duty ratio becomes less than a certain set value, the drive voltage 30 supplied to the switch type drive circuit 7 is changed to the drive voltage variable circuit. 28.

From time 19 to time 31 in FIG. 5, the duty ratio is greater than or equal to a certain set value after the start, and the supply voltage 30 to the switch type drive circuit is at a high set value 38. As the rotational speed increases, the energization duty ratio gradually decreases and when it falls below the set value at time 31, the supply drive voltage is reduced to a lower set value 3.
Gradually decrease toward 9. This was added to prevent the control system from oscillating due to sudden drive voltage fluctuations. Conversely, if a speed fluctuation occurs due to a disturbance at time 32 and an increase in the duty ratio is detected at time 33, the supply drive voltage is increased. The setting value is rapidly increased to 38 so that the responsiveness to speed fluctuations remains the same as that of the conventional example. Sections 17 and 37 are steady speed sections in which the supply drive voltage is kept at a low set value.

FIG. 6 shows a specific example of the duty ratio detection circuit 27 and the drive voltage variable circuit 28. Monostable multivibrators (hereinafter abbreviated as mono-multi) 41 and 43 are triggered by the reference clock 3, and when the energization signal 6 is completed while the mono-multi vibrator 41 is on, the set-reset type is activated via the AND gate 42. A flip-flop (hereinafter abbreviated as R-SFF) 45 is set. In this case, when the duty ratio of energization becomes smaller than the set value, the transistor 46 is turned off and the base voltage of the transistor 52 is gradually increased by the charging circuit of the variable resistor 47 and the capacitor 48, and the emitter voltage of the transistor 51 ( The supply voltage (30) to the switch type driver circuit is gradually lowered to a value determined by the ratio of the resistors 49, 50 and the input voltage (40). Also, when the energization signal 6 is completed after the monomulti 43 is turned off, the R-S・FF4
Reset 5. In this case, the transistor 46 is turned on and the capacitor 48 is
The transistor 52 is turned off by quickly discharging the charge. Along with this, the emitter voltage of the transistor 51 (supply voltage 3 to the switch type driver circuit)
0) rapidly rises to the value of input voltage 40, improving the responsiveness of the servo system.

The difference between the setting times of the monomultis 41 and 43 causes hysteresis in the duty ratio detection circuit, and by appropriately setting this difference between the setting times, there is an effect of eliminating instability in the control system.

As described above, the present invention adds a simple duty ratio detection circuit and a variable drive voltage supply circuit to the conventional pulse energization type DC servo, thereby increasing the motor supply voltage at steady speed without sacrificing the advantages of the pulse energization type. This reduces the noise generated by the motor on average, prevents the brushes of the DC motor from being worn out by high voltage sparks, and extends the life of the motor. In the present application, a duty ratio detection circuit detects whether the duty of an energization signal is within a predetermined range, and controls a power supply control circuit according to the detection result, and when the duty ratio is outside the range, the duty ratio is reduced. In this case, the drive voltage of the switch type driver circuit is gradually lowered, and in the case of a large duty ratio, the drive voltage of the switch type driver circuit is rapidly increased, so the duty ratio of the energization signal is low. This means that the load on the motor becomes lighter and the duty ratio becomes higher.
Since this means that the load on the motor becomes heavier, according to the present application, when the load becomes lighter, the supply voltage is gradually lowered, and when it becomes heavier, the supply voltage is suddenly increased, which reduces vibration, noise, etc. Smooth control without wasting energy can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional example of a pulse current type DC speed servo, and 12 is a printer carriage. FIG. 2 is a time chart illustrating the operation of the conventional example, in which 20 represents the time when the speed reached a steady value, and 21 represents the time when a stop command was issued. FIG. 3 shows a switch type drive circuit using four transistors. FIG. 4 is a block diagram showing the configuration of the present invention, and 29 is the output of the duty ratio detection circuit. FIG. 5 is a time chart explaining the operation of the present invention. Time 34 represents the time when the speed fluctuation caused by the disturbance has recovered and the energization duty ratio has become smaller than the set value. From this time, the supply to the switch type drive circuit starts. Gradually reduce the voltage. 35 represents the time when the influence of the disturbance has disappeared and the speed has returned to a steady state. Section 36 represents a response section due to disturbance. FIG. 6 shows a specific example of the duty ratio detection circuit and the variable drive voltage supply circuit.

Claims (1)

[Claims] 1. (a) A reference clock oscillator that generates a reference clock; (b) A positional relationship between the reference clock output from the oscillator and an output signal from an encoder coupled to a rotating shaft of a DC motor. (c) a switch type driver circuit that supplies power to the DC motor based on the phase difference signal output from the phase detection circuit; (d) the reference clock and the phase difference signal; a lower limit setting circuit that takes as an input the reference clock and generates an output signal after a predetermined time period corresponding to the lower limit value of the duty ratio of the phase difference signal has elapsed after inputting the reference clock; an upper limit value setting circuit that generates an output signal after a predetermined time period corresponding to the upper limit value of the duty ratio; a circuit that generates a signal indicating that the phase difference signal exceeds the lower limit of the duty ratio; a circuit that generates a signal indicating that the upper limit of the duty ratio has been exceeded; and when a signal indicating that the lower limit of the duty ratio has been exceeded, the output signal is set to a first state, and it is determined that the upper limit of the duty ratio has been exceeded; and a circuit that changes the output signal to a second state that is inverted from the first state when a signal indicating that the phase difference signal exceeds the lower limit or upper limit of a predetermined duty ratio. a duty ratio detection circuit for detecting; (e) a power supply voltage and an output signal from the duty ratio detection circuit; connected in series with the input from the power supply voltage; The first corresponding to
When a status signal is outputted, the resistance value with respect to the power supply voltage is controlled to be large, and when the duty ratio detection circuit outputs a second status signal corresponding to exceeding the upper limit of the duty ratio, the resistance value is decreased. and a drive voltage variable circuit that supplies a terminal on the side connected to the power supply voltage and a terminal on the opposite side of the variable resistance circuit as an output to the switch type driver circuit. A pulse energization type DC speed servo.