JPH08237983A - Drive circuit - Google Patents

Abstract

PURPOSE: To improve the digital drive circuit for servo motor. CONSTITUTION: The drive circuit comprises a section 21 for detecting the actual rotational speed of a servo motor M to generate a digital speed detection data KD indicative of the detection results, a section 20 for comparing a digital target speed data DD indicative of a target rotational speed of the servo motor M with the speed detection data KD to control the servo motor M digitally based on the comparison results such that the actual rotational speed of the servo motor M follows up the target rotational speed. The drive circuit further comprises an abnormal rotation protective circuit 22 for stopping the driving of the servo motor M when the difference between the speed detection data KD and the target speed data DD exceeds a predetermined value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit, and more specifically, it is an object of the present invention to improve a drive circuit for digitally controlling a servo motor used in a printer or a copying machine.

[0002]

2. Description of the Related Art A drive circuit according to a conventional example will be described below with reference to the drawings. As shown in FIG. 3, this circuit includes a CPU [Central Processing Unit] (1), a deviation counter (2), an up / down counter [hereinafter referred to as a U / D counter] (3), a digital / analog. Converter [hereinafter referred to as D / A converter]
(4) A circuit for driving a DC servo motor (M) used in a printer, a copying machine or the like, which has a motor control section (5), a comparator (6), a waveform multiplication circuit (7) and an encoder (E). It is a circuit that controls the DC servo motor (M) so that the actual rotation speed of the DC servo motor (M) follows a preset target speed.

According to this circuit, an operation command is first input to the CPU (1), and the CPU is based on this operation command.
From (1), the drive clock (fpps) is input to the deviation counter (2). The frequency of the drive clock (fpps) indicates the target speed of the DC servo motor (M) to be driven. When the target speed is high, the frequency of the drive clock (fpps) becomes high.

Then, the deviation counter (2) compares the drive clock (fpps) with the status signal (JS) which is the output of the waveform multiplication circuit (7), and the drive clock (f
If the pps) is larger than the status signal (JS), the acceleration signal (+) that instructs the acceleration of the motor is output to the U / D counter (3), and conversely the drive clock (fpps) is the status signal (JS) If it is smaller than this, a deceleration signal (-) instructing deceleration of the motor is output to the U / D counter (3).

Immediately after the circuit is started, the number of revolutions of the DC servo motor (M) is 0, so the output signal of the deviation counter (2) becomes the acceleration signal (+). Next, the output signal of the deviation counter (2) is up-counted by the U / D counter (3), and the count result is D / A converter (4).
Is input to the motor control section (5), and the count result is D / A converted and an analog signal (AD) is output to the motor control section (5).

A switching transistor (S1) which is connected to the servomotor (M) from the motor control section (5) and constitutes a bridge circuit according to the analog signal (AD) is formed.
To S4), the switching transistors (S1 to S4) are turned on / off to supply a current to the DC servo motor (M), which rotates. This D
The rotation speed of the C servo motor (M) is detected by the rotary encoder (E) at any time, and the detection result is input to the waveform multiplication circuit (7) as a detection clock (KC) and detected by the waveform multiplication circuit (7). Clock (KC)
Is multiplied by an integer to generate a status signal (JS) which is a serial signal of the same format as the driving clock (fpps) and is input to the deviation counter (2).

Then, the deviation counter (2) again compares the driving clock (fpps) with the status signal (JS), and when the driving clock (fpps) is larger than the status signal (JS), the acceleration signal (+ ) Is output to the U / D counter (3), and the servomotor (M) is accelerated.
In this way, until the actual rotation speed of the servo motor (M) reaches the target speed, in other words, the status signal (J
The servomotor (M) is accelerated until (S) reaches the drive clock (fpps).

When the status signal (JS) reaches the driving clock (fpps), the deviation counter (2) outputs neither the acceleration signal (+) nor the deceleration signal (-) at all, so that the U / D counter ( The output of 3) becomes 0, and naturally the analog signal (AD) from the D / A converter (4) is not output either, so the current supply to the servo motor (M) is stopped and the acceleration operation is stopped. (M) continues to rotate by inertia and rotates at a constant speed at a target speed for a certain period of time.

After that, since the rotation speed of the servo motor (M) which has been rotating by inertia decreases due to friction or the like, it falls below the target speed again, and the status signal (JS) falls below the drive clock (fpps). Then, since the acceleration signal (+) is output again from the deviation counter (2), the servo motor (M) is accelerated again until the target speed is reached. By repeating the above operation, the servo motor (M) operates so as to follow the target speed preset by the drive clock (fpps).

The current (Is) flowing in the servo motor (M) is constantly detected in the circuit, and an overcurrent protection circuit (stops the operation of the circuit when an overcurrent exceeding a predetermined allowable amount flows) ( PC) is provided. The current (Is) flowing in the servo motor (M) is converted into a voltage, and after noise is removed by the filter circuit (FC), it is converted by the delay circuit (CC) including the resistor (R1) and the electrolytic capacitor (C1). Delayed comparator (6)
Is input to the non-inverting input (+) of.

On the other hand, the inverting input (-) of the comparator (6)
A reference voltage (Vref) determined by the bleeder ratio of the resistors (R2, R3) is input to the. For some reason, an overcurrent flows in the servo motor (M), and the potential of the non-inverting input (+) of the comparator (6) becomes the reference voltage (Vre
When it exceeds f), the output of the comparator (6) becomes high level (hereinafter referred to as “H”), which is the CPU.
The output to (1) detects that an overcurrent has flowed, and the operation of the circuit is stopped.

The time when it is considered that an abnormality has occurred due to the flow of an overcurrent (this time is referred to as the overcurrent conduction time) is the resistance (R1) and the electrolytic capacitor (C) that constitute the delay circuit (CC).
It is set by the time constant of 1).

[0013]

However, according to the above-mentioned conventional drive circuit as shown in FIG. 3, the time (hereinafter referred to as the start time) at which the target speed should be reached after the motor is started elapses. After that, foreign matter is mixed into the motor (M) or foreign matter is caught on the rotating shaft of the motor (M), which hinders the rotation of the motor (M).
As shown in, the rotation speed becomes lower than the target speed (hereinafter, this state is referred to as abnormal rotation), and in severe cases, the motor (M) may stop completely.

When the motor (M) is completely stopped due to abnormal rotation, an overcurrent flows through the motor (M), so that an overcurrent protection circuit (P) provided in the above circuit is provided.
Although the drive of the motor (M) can be stopped by C), the time detection accuracy was low. If an overcurrent is still not detected even if abnormal rotation occurs, a current exceeding the motor or driver rating will always flow, and if left unattended, the motor will burn out or the driver will be damaged. There was a problem.

[0015]

The present invention has been made in view of the above-mentioned drawbacks of the prior art. As shown in FIG. 1, a digital signal indicating the detection result of the actual rotation speed of the servomotor is detected. The speed detection unit that generates speed detection data that is data, the target speed data that is digital data indicating the target rotation speed of the servo motor, and the speed detection data are compared, and the servo motor is based on the comparison result. When the difference between the speed detection data and the target speed data exceeds a certain value and an abnormality occurs, the drive control unit digitally controls the servo motor so that the actual rotation speed of the device follows the target rotation speed. The abnormal rotation protection circuit that stops the drive of the servo motor is reliably provided to detect the abnormal rotation of the motor and to prevent damage to the motor due to the abnormal rotation. It is an object to provide a drive circuit which makes it possible to suppress.

[0016]

[Operation] According to the present invention, as shown in FIG. 1, a speed detection unit that detects the actual rotation speed of the servo motor and generates speed detection data that is digital data indicating the detection result; The target speed data, which is the digital data indicating the target rotation speed of the motor, is compared with the speed detection data, and the servo motor is digitally adjusted so that the actual rotation speed of the servo motor follows the target rotation speed based on the comparison result. It has a drive control unit for controlling, and an abnormal rotation protection circuit for stopping the drive of the servo motor when the difference between the speed detection data and the target speed data exceeds a certain value and an abnormality occurs.

Therefore, since the difference between the speed detection data and the target speed data is constantly calculated by the abnormal rotation protection circuit, and the servo motor is stopped when the rotation exceeds the predetermined value and abnormal rotation occurs, The abnormal rotation can be detected more reliably than in the conventional case where the abnormal rotation of the motor is detected by a method with low detection accuracy of detecting overcurrent.

This makes it possible to prevent abnormal rotation from being reliably detected as in the conventional case, and to prevent burning of a motor or the like if left unattended.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A drive circuit according to an embodiment of the present invention will be described below with reference to the drawings. The drive circuit according to the present embodiment is used in an OA device such as a printer or a copying machine.
It is a drive circuit for driving and controlling the C servo motor.
This drive circuit, as shown in FIG.
0), speed detector (21), abnormal rotation protection circuit (22)
And a circuit for driving the servo motor (M) so as to follow a preset target rotation state, which has an overcurrent protection circuit (30).

The drive control section (20) includes a latch circuit (11
A, 11B), comparator (12), up-down pulse generation circuit (13), up-down counter (1
4), having a PWM (Pulse Width Modulation) circuit (15), a pre-driver (16) and switching transistors (S11-S14), comparing target speed data (DD) and detected speed data (KD) Then, the servo motor (M) is controlled so that the detected speed data (KD) follows the target speed data (DD).

The speed detecting section (21) has a rotary encoder (E), a multiplication circuit (17) and a serial / parallel conversion circuit (18), and the rotational speed of the servomotor (M) detected by the rotary encoder (E). Is a circuit for detecting detected speed data and generating detected speed data (KD). The abnormal rotation protection circuit (22) includes a lock detection circuit (23), a delay circuit (24), a protection circuit (25), and a clock generation circuit (2).
6) and a time constant circuit (27), which calculates a difference between the target speed data (DD) and the detected speed data (KD), and when the difference exceeds a certain value and abnormal rotation occurs. Is a protection circuit for forcibly stopping the drive of the servo motor (M).

The overcurrent protection circuit (30) has a comparator (29A) and a delay circuit (29B), and forcibly rotates the servomotor (M) when an overcurrent flows through the servomotor (M). It is a protection circuit to stop. In the drive control unit (20), the latch circuit (11A) has a C (not shown).
The target speed data (DD) output from PU is latched and output to the comparator (12), and the latch circuit (11B) latches the detected speed data (KD) and outputs to the comparator (12). To do.

Further, the comparator (12) has a target speed data (DD) and 6-bit speed detection data (K
D) and the comparison result, and the comparison result is an up / down pulse generation circuit [hereinafter referred to as U / D pulse generation circuit].
It is a circuit for outputting to (13). Specifically, when the target speed data (DD) is larger than the speed detection data (KD), a high level (hereinafter referred to as “H”) signal is output, and conversely, the target speed data (DD) is the speed detection data. When it is smaller than (KD), it is low level (hereinafter "L").
Signal) is output.

The U / D pulse generation circuit (13) generates a predetermined U / D pulse signal (UP) based on the output signal of the comparator (12) and an up / down counter [hereinafter referred to as U / D counter]. This is a circuit for outputting to (14). Specifically, when the output signal of the comparator (12) is "H", a maximum of 2 6 = 63 serial pulse signals per unit of time U / D pulse signal (U
P) is output.

The U / D counter (14) has a U / D pulse signal (U) input from the U / D pulse generation circuit (13).
The pulse number of P) is counted, converted into 6-bit parallel data according to the counted number, and the PWM circuit (1
Output to 5). The PWM circuit (15) sequentially takes in 6-bit parallel data output from the U / D counter (14) and PWM-modulates the duty ratio of a drive pulse (PP) for driving the servo motor (M). The PWM pulse (PW) for setting is output.

For example, if the data from the U / D counter is 3F
In other words, if it is 63, a PWM pulse (PW) with a duty ratio of 100%, and if it is 0, a PWM pulse (PW) is generated and output. The pre-driver (16) is a circuit that supplies a drive pulse (PP) to the switching transistors (S11 to S14) that are MOS transistors based on a PWM pulse (PW) output via a protection circuit (25) described later. is there.

These four switching transistors (S11 to S14) constitute a bridge circuit, and these ON / OFF operations are performed to supply / non-supply current to the servo motor (M), whereby the servo motor ( M) rotates, and the servomotor (M) is drive-controlled so as to perform any one of a forward rotation operation, a reverse rotation operation, and a desired stop operation.
In the speed detection unit (21), the encoder (E) detects the rotation speed and position of the servo motor (M) at any time,
The rotary encoder outputs the detection results as digital data to the multiplication circuit (18). In this embodiment, a rotary encoder having a resolution of 100 pulses / rev is used.

The multiplication circuit (17) is a circuit for multiplying the detection result output from the encoder (E) by an integer and outputting the result to the serial / parallel conversion circuit (18). The serial / parallel conversion circuit (18) is a circuit that performs serial / parallel conversion on the output of the multiplication circuit (17) to generate speed detection data (KD). In the abnormal rotation protection circuit (22),
The lock detection circuit (23) is an example of an abnormal rotation detection circuit, and calculates the difference between the target speed data (DD) and the speed detection data (KD) output from the latch circuits (11A, 11B), and calculates the difference. Is a circuit that outputs an abnormal rotation detection signal (RS) of "H" when exceeds a preset constant value.

The delay circuit (24) has an abnormal rotation detection signal (R) for a delay time which is a constant time set based on a divided clock output from a time constant circuit (27) described later.
It is a circuit for delaying S) and outputting it to the protection circuit (25). When the abnormal rotation detection signal (RS) of "H" delayed by the delay circuit (24) is input, the protection circuit (25) forcibly stops the operation of the pre-driver (16) and the servo motor (25). This is a circuit for stopping the driving of (M).

The clock generation circuit (26) is a circuit for outputting the reference clock (CK) to the time constant circuit (27), and the time constant circuit (27) sets a 2-bit delay time input to itself. It is a circuit that divides the reference clock (CK) with a division ratio defined by the data (t0, t1) and outputs the divided frequency to the delay circuit (24). Overcurrent protection circuit (3
0), the comparator (29A) converts the voltage, and then the noise is removed by the filter circuit (FL), the current flowing through the servo motor (M) and the resistance (R).
11, R12) is compared with a reference voltage (Vref) determined by a bleeder ratio, and when this exceeds a reference voltage (Vref), a high level (hereinafter referred to as “H”) overcurrent detection signal (hereinafter referred to as “H”) KK) is output to the delay circuit (24).

The delay circuit (29B) is a time constant circuit (2
This circuit delays the overcurrent detection signal (KK) by a delay time which is a constant time set based on the divided clock output from 7) and outputs the overcurrent detection signal (KK) to the protection circuit (25). The operation of the above circuit will be described below. First CPU
When the operation command is input to (11), the target speed data (DD) corresponding to the operation command is output from the CPU (11).

The target speed data (DD) is 6-bit digital data indicating the target speed of the servo motor (M). In this embodiment, target speed data (DD)
Is 6-bit digital data, so "00"
It is possible to set a value from "0000", that is, 0 to "111111", that is, 63. In this embodiment, the resolution of the encoder circuit (E) is 100 pulses / rev.
Therefore, by setting 1 bit of this target speed data (DD) to 100 rpm, it becomes possible to set the target speed from 0 rpm to 6300 rpm in steps of 100 rpm. Here, "111111" is output from the CPU (11) and the target speed is 6300 rpm.
Is set to.

Next, the comparator (12) compares the target speed data (DD) with the speed detection data (KD). Immediately after starting the circuit, the servo motor (M)
Since the rotation speed of is 0, the speed detection data (KD) is "00".
Since the target speed data (DD) which is "111111" is larger, the output of the comparator (12) becomes "H".

When "H" is output from the comparator (12), the U / D pulse generator (13) outputs a maximum of 2 6 = 63 pulse signals per time unit (50 ms in this embodiment). It outputs a certain U / D pulse signal (UP). Next, the U / D pulse signal (UP) is counted by the U / D counter (14), and 6 is counted according to the count number.
Bit parallel data (in this case, "11111"
1 ") and output to the PWM circuit (15).

Next, the 6-bit parallel data as the count result of the U / D counter (14) is converted into the PWM circuit (1
PWM modulation is performed by 5), and the duty ratio of the PWM pulse (PW) for driving the motor is set. This duty ratio increases or decreases depending on the size of the 6-bit parallel data output from the U / D counter (14),
For example, if this data is 3F, that is, 63, the duty ratio is 100%, and if it is 0, the PWM pulse (PW) with the duty ratio of 0% is output.

After that, the drive pulse (P) according to the duty ratio of the PWM pulse output from the PWM circuit (15) is generated.
P) is output from the pre-driver (16) to the MOS type switching transistors (S11 to S14), and these switching transistors (S11 to S14) are PW.
The servo motor (M) performs a predetermined rotation by performing ON / OFF operation according to the duty ratio set by the M circuit (15).

That is, when the motor is normally rotated, the switching transistors (S12, S13) among the switching transistors are always turned off, and the PWM
The drive pulse (PP) having the duty ratio set by the circuit (15) is used to switch the switching transistors (S11, S).
14) is turned on / off to supply a current to the servo motor (M) to rotate it forward.

The actual rotation speed of the servomotor (M) is constantly detected by the encoder circuit (E), and the detection result is output to the multiplication circuit (17). The detection result is multiplied by an integer by the multiplication circuit (17), and then serial / parallel converted by the serial / parallel conversion circuit (18), so that the servo motor (M)
Shows the actual detection result of the rotation speed, and speed detection data (KD) which is parallel 6-bit digital data is generated and output to the comparator (12).

Then, the comparator 12 again compares the target speed data (DD) with the speed detection data (KD). The rotational speed increases and the speed detection data (KD) increases as the servo motor (M) accelerates, but if the target speed data (DD) is still larger than the speed detection data (KD), "H". Is output.

In this way, until the actual rotation speed of the servo motor (M) reaches the target speed of 6300 rpm, in other words, the speed detection data (KD) is "1111".
The servo motor (M) is accelerated until the target speed data (DD) of 11 "is reached.
When D) reaches the target speed data (DD), "L" is output from the comparator (12), so the U / D pulse generation circuit (13) stops the generation of the U / D pulse signal (UP). Therefore, the output of the U / D counter (14) becomes zero.

Therefore, since the count result is not output to the PWM circuit (15) and the PWM pulse having the duty ratio of 0 is generated, the current supply to the servo motor (M) is stopped and the acceleration operation is stopped. The servomotor (M) continues to rotate by inertia and rotates at a constant speed at a target speed for a certain period of time. afterwards,
Since the rotation speed of the servo motor (M) that was rotating by inertia decreases due to friction or the like, the target speed is 63% again.
Below 00 rpm, the speed detection data (KD) falls below the target speed data (DD). Then again comparator (1
Since the output of 2) becomes "H", the above operation is repeated and the servomotor (M) is accelerated again until the target speed is reached. By repeating the above operation, the servo motor (M) operates so as to follow the target speed of 6300 rpm preset by the target speed data (DD).

In the following, the rotation of the motor (M) is interrupted by some abnormality such as foreign matter mixed in the motor, which is a characteristic operation of the drive circuit of the present invention, and the rotation speed is lower than the target speed. The case where the abnormal rotation of becoming low occurs will be described below. In the above circuit, the target speed data (DD) and the speed detection data (KD) are constantly output from the latch circuit (11A, 11B) to the lock detection circuit (23).
Is input to

The lock detection circuit (23) constantly calculates the difference between the target speed data (DD) and the speed detection data (KD), and when this difference exceeds a preset constant value, It is judged that the servo motor (M) is abnormally rotating, and the "H" abnormal rotation detection signal (RS) is output to the delay circuit (2).
Output to 4). Then, the abnormal rotation detection signal (RS) delayed by the delay time described below is transmitted to the delay circuit (2
When output from 4) to the protection circuit (25), the protection circuit (25) can forcibly stop the operation of the pre-driver (16) and stop the driving of the servo motor (M).

The method of setting the above-mentioned delay time will be described below. First, the reference clock (CK) is input from the clock generation circuit (26) to the time constant circuit (27).
The delay time defining data (t0, t1), which is 2-bit digital data, is simultaneously input to the time constant circuit (27), and the delay time defining data (t0, t1) has a frequency division ratio set by the division ratio. The reference clock (CK) is divided and output to the delay circuit (24).

Since the delay time defining data (t0, t1) is 2-bit digital data, as shown in the timing chart of FIG. 2, depending on the combination of (t0, t1), 2 squared, that is, four different types of data. It is possible to generate clocks (CK1 to CK4) having a frequency ratio. For example, the delay time definition data (t0, t1) is "1",
When it is "0", the set time is "1" of (t0, t1),
A division clock (C with a division ratio of 1/2 based on "0")
K2) is generated and delay time specification data (t0, t1)
Are "1" and "1", respectively, the divided clock (CK4) having a dividing ratio of 1/8 is output.

These four types of divided clocks (CK1 to CK1
One of the divided clocks specified by the delay time specification data (t0, t1) in CK4) is the delay circuit (2
It is output to 4). Then, by the delay circuit (24),
The divided clock (CK) output from the time constant circuit (27)
1 to CK4), the abnormal rotation detection signal (RS) output from the lock detection circuit (23) is output to the protection circuit (25) at the time of this detection (tt1 to tt4). For example, when the delay time defining data (t0, t1) are "1" and "1", respectively, the divided clock (CK
An abnormal rotation detection signal (RS) is output to the protection circuit (25) at the time of rising edge detection (tt4) in 4).

From the above, the delay time defining data (t0, t
The delay time as shown in Table 1 below is set by 1).

[0048]

[Table 1]

For example, from Table 1 above, when the delay time defining data (t0, t1) is "0" and "0", the delay time is 50 msec, and when it is "1" and "1", the delay time is 400 msec. Becomes As an example, although the delay time defining data (t0, t1) are "0" and "0", respectively, and the target speed data (DD) is "111111", the detected speed data (KD) is "00011
In this case, the lock detection circuit (23) determines the difference "1110".
00 "is calculated. Since this value is very large, the abnormal rotation detection signal (RS) is output from the lock detection circuit (23), and this is output to the delay circuit (24). It is delayed by 50 msec which is a delay time defined by the time definition data (t0, t1) and output to the protection circuit (25), and the protection circuit (25) forcibly stops the operation of the pre-driver (16). The drive control of the servo motor (M) stops.

As described above, according to the drive circuit of this embodiment, when the difference between the speed detection data (KD) and the target speed data (DD) exceeds a certain value and an abnormality occurs, the servo motor It has an abnormal rotation protection circuit (22) for forcibly stopping the driving of (M). Therefore, the speed detection data (KD) and the target speed data (DD) are constantly compared,
When the difference exceeds a certain value, the abnormal rotation detection signal (RS) is output to the protection circuit (25) to stop the driving of the servo motor, so that a method with low detection accuracy of detecting an overcurrent. Thus, it becomes possible to reliably detect the abnormal rotation as compared with the conventional case in which the abnormal rotation of the servo motor (M) is detected.

As a result, it is possible to prevent abnormal rotation of the servo motor (M) from being reliably detected as in the conventional case, and to prevent the servo motor (M) from being damaged by burning or the like if left unattended. . Further, it is of course possible to obtain the same effect even when the motor is completely stopped due to a large degree of abnormal rotation. Further, in the drive circuit according to the present embodiment, like the abnormal rotation protection circuit (22), an overcurrent protection circuit that forcibly stops the operation of the circuit after delaying the delay time after detecting the overcurrent. (30) is provided, but this delay time is calculated by using the clock generation circuit (26) and the time constant circuit (27) provided in the abnormal rotation protection circuit (22). Since it is set by t1) and activated with the same delay time, it is not necessary to provide a circuit for setting the delay time for each of the two types of protection circuits, and a circuit is provided as compared with the case where this is provided separately. It is possible to reduce the cost required for.

In this embodiment, the target speed data (D
Although D) is 6-bit digital data, the present invention is not limited to this, and the same effect can be obtained regardless of how it is set to 4 bits, 10 bits or the like according to the application of the servo motor. Also, the delay time can be set with 2-bit digital data and is 50, 100, 150, 200 ms.
Although four types of time ec are set, the present invention is not limited to this, and the same effect can be obtained even if eight types of time are set using, for example, 3-bit data.

[0053]

As described above, according to the drive circuit of the present invention, when the difference between the speed detection data and the target speed data exceeds a certain value and the abnormality occurs, the drive of the servo motor is stopped. Has a rotation protection circuit. For this reason, when the difference between the speed detection data and the target speed data exceeds a certain value, the abnormal rotation is detected and the servomotor drive is stopped. The abnormal rotation can be detected more reliably than in the conventional case where the abnormal rotation of the motor is detected by the low method.

As a result, it is possible to prevent abnormal rotation from being reliably detected as in the conventional case, and to prevent burning of the motor or the like if left unattended.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a drive circuit according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating the operation of the time constant circuit and the delay circuit according to the exemplary embodiment of the present invention.

FIG. 3 is a circuit diagram of a drive circuit according to a conventional example.

FIG. 4 is a graph illustrating abnormal rotation of a servo motor.

[Explanation of symbols]

 (11) CPU (12) Comparator (13) U / D pulse generation circuit (14) U / D counter (15) PWM circuit (16) Pre-driver (17) Multiplication circuit (18) Serial / parallel conversion circuit (20) Drive control unit (21) Speed detection unit (22) Abnormal rotation protection circuit (23) Lock detection circuit (abnormal rotation detection circuit) (24) Delay circuit (25) Protection circuit (26) Clock generation circuit (27) Time constant circuit (28) Rotation direction detection circuit (29A) Comparator (29B) Delay circuit (30) Overcurrent detection circuit (M) Servo motor (S11 to S14) Switching transistor (DD) Target speed data (KD) Speed detection data (RS) Abnormal rotation detection signal (KK) Overcurrent detection signal (t0, t1) Delay time specification data

Claims (2)

[Claims] 1. A speed detection unit that detects an actual rotation speed of a servo motor and generates speed detection data that is digital data indicating the detection result, and digital data that indicates a target rotation speed of the servo motor. A drive control unit that compares the target speed data with the speed detection data and digitally controls the servo motor so that the actual rotation speed of the servo motor follows the target rotation speed based on the comparison result. A drive circuit having an abnormal rotation protection circuit for stopping the drive of the servo motor when the difference between the speed detection data and the target speed data exceeds a certain value and an abnormality occurs. 2. The abnormal rotation detection circuit, which outputs an abnormal rotation detection signal when the difference between the speed detection data and the target speed data exceeds a certain value, and the abnormal rotation detection signal. A time constant circuit that generates a delay time, a delay circuit that delays the abnormal rotation detection signal by the delay time, and a protection circuit that stops the operation of the circuit based on the delayed abnormal rotation detection signal. The drive circuit according to claim 1, wherein the drive circuit is a drive circuit.