JPH08237976A - Drive circuit - Google Patents

Abstract

PURPOSE: To improve the 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 produce a digital data indicating the detection results, i.e., a speed detection data KD, and a section 20 for comparing a digital data indicating a target rotational speed of the servo motor M, i.e., a target speed data, with the speed detection data, to control the servo motor M such that the actual rotational speed follows up the target rotational speed. The drive control section 20 varies the starting time, i.e., the time being elapsed before the servo motor M reaches the target rotational speed, based on a digital starting time set data T0, T1.

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. 4, this circuit includes a CPU [Central Processing Unit] (1), a deviation counter (2), an up / down counter [hereinafter referred to as U / D counter] (3), a digital / analog. Converter [hereinafter referred to as D / A converter]
(4), buffer amplifier (BU), motor control unit (5), waveform multiplication circuit (6) and encoder (E), and a circuit for driving a DC servo motor (M) used in a printer, a copier or the like A circuit for controlling 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, and 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 (6), and the drive clock (fpps).
) Is larger than the status signal (JS), the acceleration signal (+) that instructs the acceleration of the servo 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 the above, a deceleration signal (-) instructing deceleration of the servo motor is output to the U / D counter (3). The output signal of the deviation counter (2) is the acceleration signal (+) because the number of revolutions of the DC servo motor (M) is 0 immediately after the activation of the circuit.

Next, the output signal of the deviation counter (2) is up-counted by the U / D counter (3), the count result is input to the D / A converter (4), and this count result is D / A converted. And analog signal (AD)
Is generated and output to the buffer amplifier (BU). A resistor (R) and an electrolytic capacitor (C) that are grounded are connected to the input of the buffer amplifier (BU), and input to the buffer amplifier (BU) after being delayed by a fixed time determined by these time constants. And analog signal (AD)
Is amplified to the drive level of the motor control unit (5) and then output to the motor control unit (5).

According to the analog signal (AD), a predetermined current is supplied from the motor controller (5) to the DC servo motor (M).
Is supplied to the DC servo motor (M) to start rotation,
To accelerate. The rotation speed of the DC servo motor (M) is detected by the rotary encoder (E) at any time,
The detection result is input to the waveform multiplication circuit (6) as a detection clock (KC), and the detection clock (KC) is multiplied by an integer by the waveform multiplication circuit (6) to drive the clock (fpps).
Status signal (JS) which is a serial signal of the same format as
Is generated and input to the deviation counter (2).

Then, the deviation counter (2) again compares the driving clock (fpps) with the status signal (JS), and if the driving clock (fpps) is larger than the status signal (JS), the acceleration signal (+). Is a U / D counter (3)
The servo motor (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 (JS) reaches the drive clock (fpps), the servo motor (M)
Is accelerated.

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, the current supply to the servo motor (M) is stopped, the acceleration operation is stopped, the servo motor (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).

After the above operation, the servo motor (M) reaches the target speed, but the time from the start of the drive circuit as shown in the graph of FIG. 5 until the target speed (n0) is reached (hereinafter This is referred to as the startup time) Δt is preset by the circuit. To make this setting,
A resistor (R) connected to the input of the buffer amplifier (BU)
And the time constants of the electrolytic capacitor (C) are adjusted. By adjusting this time constant, the analog signal (A
The time delayed when D) is input to the buffer amplifier (BU) (hereinafter referred to as delay time) changes.
That is, if the delay time is short, the startup time is short, and if the delay time is long, the startup time is long. Therefore, by changing the capacitance of the electrolytic capacitor (C) to adjust the delay time, the startup time (Δt) can be reduced. I was adjusting.

[0011]

However, according to the above-mentioned conventional drive circuit, the start-up time depends on the buffer amplifier (B
Although it is set by the time constant of the resistance (R) connected to the input of U) and the electrolytic capacitor (C), this electrolytic capacitor (C) is prone to deterioration with the passage of time and has a large variation in characteristics. Since it is a low-reliability element, there has been a problem that it is extremely difficult to precisely set the startup time.

Further, if it is desired to change the start-up time of the circuit for some reason, the start-up time cannot be changed unless the electrolytic capacitor is replaced, so that the start-up time cannot be changed easily.

[0013]

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. And a drive control unit for digitally controlling the servomotor so that the actual rotation speed of the servomotor follows the target rotation speed, and the drive control unit controls the servomotor based on start time setting data which is digital data. By changing the start-up time, which is the time it takes for the motor to reach the target rotation speed, the start-up time can be set without using an unreliable electrolytic capacitor. And, and it is an object to provide a drive circuit which makes it possible to easily start the time change.

[0014]

[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 digital data indicating the target rotation speed of the motor, is compared with the speed detection data, and the servo motor is digitalized so that the actual rotation speed of the servo motor follows the target rotation speed based on the comparison result. And a drive control unit that controls the drive control unit, and the drive control unit changes the activation time, which is the time until the servomotor reaches the target rotation speed, based on the activation time setting data that is digital data.

For this reason, the drive control unit sets the starting time based on the starting time setting data which is digital data, instead of setting the starting time using the electrolytic capacitor which is a low reliability element as in the prior art. Therefore, it becomes possible to set the starting time more precisely than in the conventional case where the starting time is set using the electrolytic capacitor. There is also an advantage that the startup time hardly changes with time.

As a result, the start-up time can be set with high accuracy, and even if the start-up time is to be changed, it is not necessary to replace the parts as in the conventional case.
It is possible to easily deal with this by simply changing the startup time setting data. In particular, the drive circuit is a hybrid IC
In the case of mounting and supplying the data to the startup time setting data, even if there is a request for different startup times in response to various user requests, even without the work of replacing electrolytic capacitors etc. according to different requests This is effective because it can be easily adapted to each request simply by changing.

In the drive circuit according to the present invention, the drive control section includes a comparator, a pulse generation circuit, an up / down counter, a PWM circuit, a pre-driver,
It has a switching transistor and the pulse generation circuit
The frequency of the pulse signal is determined based on the start time setting data. That is, the target speed data and the speed detection data are compared by the comparator, the U / D pulse generating circuit generates a pulse signal according to the output of the comparator, the up / down counter counts the pulse signal, and the PWM circuit up / down counter. A drive pulse whose duty ratio is determined based on the count result of is generated, and the pre-driver performs switching drive of the switching transistor based on the drive pulse.
Current is supplied / non-supplied to the servo motor by the switching transistor to control the drive of the servo motor, and the frequency of the pulse signal generated by the pulse generation circuit is determined based on the start time setting data input to the pulse generation circuit. To do.

Therefore, the frequency of the pulse signal changes according to the start time setting data, and the rotation speed until the servo motor reaches the target rotation speed (hereinafter referred to as the start rotation speed) is determined based on this. For example, when the frequency of the pulse signal increases, the count number of the up / down counter increases and the duty ratio of the drive pulse set by the PWM circuit increases, so that the startup rotation speed of the servo motor increases, and conversely the pulse signal When the pulse frequency decreases, the starting rotation speed of the servo motor decreases.

The start-up time, which is the time until the target speed is reached, is shortened when the start-up rotation speed is high, and the start-up time is increased when the start-up rotation speed is slow, so that the start-up time setting data is changed. By doing so, the startup time can be adjusted.

[0020]

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) A circuit for controlling the servo motor (M) so that the detected speed data (KD) follows the target speed data (DD).
It is also a circuit that adjusts the starting time, which is the time until the target speed is reached, based on the starting time setting data (T0, T1).

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 circuit including a time constant circuit (27), when a difference between the target speed data (DD) and the detected speed data (KD) is calculated, and an abnormal rotation occurs when this difference exceeds a certain value. 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) which will be described later.
D), and the comparison result is an up / down pulse generation circuit [hereinafter referred to as U / D pulse generation circuit] (1
It is a circuit for outputting to 3). 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. (K
When it is smaller than D), a low level (hereinafter referred to as "L") signal is output.

The U / D pulse generation circuit (13) is an example of a pulse signal generation circuit, and generates a predetermined U / D pulse signal (UP) based on the output signal of the comparator (12) to generate an up / down counter. [Hereinafter, referred to as U / D counter] It 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 U / D pulse signals (UP) that are serial pulse signals are output per unit of time. There is.

This U / D pulse signal (UP) is the U / D
The frequency changes based on the start time setting data (T0, T1) input to the pulse generation circuit (13).
Details of this setting will be described later. The U / D counter (14) counts the pulse number of the U / D pulse signal (UP) input from the U / D pulse generation circuit (13) and converts it into 6-bit parallel data according to the counted number. And outputs it to the PWM circuit (15).

The PWM circuit (15) sequentially takes in the 6-bit parallel data output from the U / D counter (14) and performs PWM modulation to drive the servo motor (M), and a drive pulse (PP). The PWM pulse (PW) for setting the duty ratio of is output. For example, if the data from the U / D counter is 3F, that is, 63, a PWM pulse (PW) with a duty ratio of 100% and 0 is generated and output if it is 0.

The pre-driver (16) supplies a drive pulse (PP) to the MOS transistors (S11 to S14), which are switching transistors, based on a PWM pulse (PW) output via a protection circuit (25) described later. It is a circuit to do. These four MOS transistors (S1
1 to S14) form a bridge circuit, and these perform ON / OFF operations to supply / non-supply current to the servo motor (M), whereby the servo motor (M) rotates,
The servo motor (M) is drive-controlled so that desired forward rotation operation, reverse rotation operation, and stop operation can be performed.

In the speed detecting section (21), the encoder (E) detects the rotational speed, the position, etc. of the servo motor (M) at any time, and outputs the detection results as digital data to the multiplication circuit (18). It is a rotary encoder. 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) performs serial / parallel conversion on the output of the multiplication circuit (17),
It is a circuit that generates speed detection data (KD). The operation of the above circuit will be described below. First, CPU (1
When the operation command is input to 1), 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. In this case, the CPU (11) outputs "111111" 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 rotation speed of the servo motor (M) is 0, so the speed detection data (KD) is "0000."
00 ", and the target speed data (DD)" 111111 "is larger, so the output of the comparator (12) becomes" H ".

When "H" is output from the comparator (12), the U / D pulse generation circuit (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.
Converted to bit parallel data, PWM circuit (1
It is output to 5).

Next, the 6-bit parallel data which is 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 servo 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 0, the duty ratio is 0. % P
The WM pulse (PW) 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).

For example, when the servomotor is normally rotated, the switching transistors (S12, S13) among the switching transistors are always turned off, and P
The switching transistor (S1) is driven by the drive pulse (PP) having the duty ratio set by the WM circuit (15).
1, S14) are turned ON / OFF to supply a current to the servo motor (M), which is normally rotated.

The actual rotation speed of the servo motor (M) is constantly detected by the encoder circuit (E), and the detection result is output to the multiplication circuit (18). The detection result is multiplied by an integer by the multiplication circuit (18), and then serial / parallel converted by the serial / parallel conversion circuit (19), 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 target speed data (DD) and the speed detection data (KD) are compared again by the comparator (12). 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) reaches the target speed data (DD) of "111111". ) Is accelerated.

When the speed detection data (KD) eventually reaches the target speed data (DD), "L" is output from the comparator (12), so the U / D pulse generation circuit (1
3) stops generation of the U / D pulse signal (UP), so that the output of the U / D counter (14) becomes zero. Therefore P
Since the count result is not output to the WM circuit (15) and a PWM pulse having a duty ratio of 0 is generated, the current supply to the servo motor (M) is stopped, the acceleration operation is stopped, and the servo motor (M) is stopped. ) Continues to rotate by inertia and rotates at a constant speed at the target speed for a certain period of time.

After that, since the rotation speed of the servo motor (M) which was rotating by inertia decreases due to friction or the like, it falls below the target speed of 6300 rpm again, and the speed detection data (KD) becomes equal to the target speed data (DD). Fall below. Then, the output of the comparator (12) becomes "H" again.
By repeating the above operation, the servo motor (M) is accelerated again until the target speed is reached. By repeating the above operation, the servo motor (M) has a target speed 630 which is a target speed preset by the target speed data (DD).
Operates so as to follow 0 rpm.

The setting of the starting time, which is a characteristic operation of the drive circuit of the present invention, will be described below. In the circuit of this embodiment, the pulse frequency of the U / D pulse signal (UP) is set by the start time setting data (T0, T1) which is 2-bit digital data. Since the start-up time setting data (T0, T1) is 2-bit digital data, it can take 2 squares = 4 types of values.

Therefore, the U / D pulse signal (UP) is shown in FIG.
Any of the clocks (CK1 to CK4) having four kinds of frequencies as shown in the timing chart of FIG. For example, when the start time setting data (T0, T1) is "0", "0", four clocks (CK1 to C)
The fastest clock (CK1) in K4) is generated, and the start time setting data (T0, T1) is “1”,
When "1", the slowest clock (CK4) among the four clocks (CK1 to CK4) is generated.

The drive control unit (20) is a servo motor (M).
It is this pulse frequency that determines the rotational speed of the. That is, when the pulse frequency of the U / D pulse signal (UP) increases, the count number of the U / D pulse signal (UP) by the U / D counter (14) increases and the PWM circuit (1
The duty ratio of the drive pulse (PP) set by 5) increases, the switching speed of the switching transistors (S11 to S14) by driving the pre-driver (16) increases, and the rotation speed of the servo motor (M) increases. To do.

Similarly, when the pulse frequency of the U / D pulse signal (UP) decreases, the rotation speed of the servo motor (M) decreases. The change with time of the rotation speed of the servo motor (M) corresponding to such four types of start time setting data (T0, T1) will be described with reference to the graph of FIG. The four types of clocks (CK1
~ CK4), the rotation speed of the servo motor (M) changes as shown in FIG.

As the rotation speed of the servo motor becomes faster, the target speed is naturally reached faster, so the starting time becomes shorter.
As shown in, the activation time corresponding to the fastest clock (CK1) is as short as 50 msec. Further, if the rotation speed of the servo motor becomes slower, the target speed is naturally reached later, so the starting time becomes longer, and the starting time corresponding to the slowest clock (CK4) is the slowest at 400 msec.

Summarizing the above, it is understood that four kinds of starting times as shown in Table 1 below can be set by the starting time setting data (T0, T1).

[0047]

[Table 1]

As described above, according to the drive circuit of this embodiment, the drive controller (20) includes the comparator (12), the U / D pulse generation circuit (13), and the U / D.
The counter (14), the PWM circuit (15), the pre-driver (16), and the switching transistors (S11-S11).
U / D pulse generation circuit (13) having S14)
Is U / based on the start time setting data (T0, T1)
The frequency of the D pulse signal (UP) is determined.

Therefore, the start time setting data (T0, T
1) changes the pulse frequency of the U / D pulse signal (UP), and based on this, the rotation speed until the servomotor (M) reaches the target rotation speed (hereinafter referred to as the starting rotation speed) is determined. For example, U / D pulse signal (UP)
The higher the frequency of, the higher the count number of the U / D counter (14) and the higher the duty ratio of the drive pulse (PP) set by the PWM circuit (15). The speed becomes faster, and conversely U /
When the pulse frequency of the D pulse signal (UP) decreases, the starting rotation speed of the servo motor (M) decreases.

If the starting rotation speed is high, the starting time, which is the time until the target speed is reached, becomes short, and if the rotation speed is slow, the starting time becomes long. In this way, the start-up time can be easily adjusted by changing the start-up time setting data (T0, T1). As a result, the starting time is set based on the starting time setting data (T0, T1), which is digital data, instead of setting the starting time using the electrolytic capacitor, which is a low-reliability element as in the related art. Therefore, it is unlikely that the startup time will fluctuate unless the clock arrives. Therefore, it becomes possible to improve the reliability of setting the startup time as compared with the conventional case.

Therefore, the start-up time can be set accurately, and even if the start-up time is to be changed, the start-up time setting data (T0, T1) can be set without replacing parts as in the conventional case. ), It becomes possible to deal with it easily. In particular, when the drive circuit is mounted on a hybrid IC and supplied, even when there is a request for different startup times in response to various user requests, work such as replacing electrolytic capacitors according to different requests is performed. Even if there is no start time setting data (T0, T
This is effective because it is possible to easily meet each request simply by changing 1).

Further, the drive circuit according to the present embodiment includes an abnormal rotation protection circuit (22) for forcibly stopping the circuit operation when the servo motor makes an abnormal rotation, and a circuit concerned when an overcurrent is detected. There are two protection circuits, an overcurrent protection circuit (30) for forcibly stopping the operation of the above, and until the protection circuit (22, 30) detects an abnormality until the circuit operation is stopped. The delay time which is the time of is set by the delay time defining data (t0, t1) which is 2-bit digital data.

In the drive circuit according to this embodiment, the delay time defining data (t0, t1) for setting this delay time and the starting time setting data (T0, T1) are separately provided.
Since both are the same 2-bit digital data, even if they are shared, the same effect can be obtained. In the present embodiment, the target speed data (DD) is 6-bit digital data, but the present invention is not limited to this. For example, 4 bits or 10 bits may be set according to the application of the servo motor. However, the same effect is obtained.

The start time is set to 50, 100, 20 by setting the start time setting data (T0, T1) of 2 bits.
Although four kinds of times of 0,400 msec are set, the present invention is not limited to this, and, for example, 8 bits by using 3-bit data.
The same effect can be obtained even if the types of time are set. Furthermore,
In this embodiment, the time from when the servo motor starts rotating to when it reaches the target speed is described as the start time, but the start time in the present invention is not limited to this, and for example, at a predetermined target speed. This is also called the start-up time when the servo motor that was being driven is switched to a target speed that is slower than that, and when switching from the first target speed to the next target speed, this is also called the start time. In the case of reversing, the time required to reach the target speed after reversing is included in the starting time in the present invention, and the same effect is obtained.

[0055]

As described above, according to the present invention, a speed detecting section for detecting an actual rotation speed of a servo motor and generating speed detection data, which is digital data showing the detection result, and a servo motor. The target speed data, which is the digital data indicating the target rotation speed, is compared with the speed detection data, and the servo motor is digitally controlled so that the actual rotation speed of the servo motor follows the target rotation speed based on the comparison result. The drive control unit changes the start time which is the time until the servo motor reaches the target rotation speed based on the start time setting data which is digital data.

Therefore, the starting time is set based on the starting time setting data, which is digital data, instead of setting the starting time using an electrolytic capacitor, which is a low-reliability element as in the prior art. The startup time can be set accurately, and even if it is changed, it is easy to change the startup time setting data without changing parts as in the past. It becomes possible to do.

[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 explaining the operation of the U / D pulse generation circuit according to the embodiment of the present invention.

FIG. 3 is a graph illustrating the operation of adjusting the startup time by the drive circuit according to the embodiment of the present invention.

FIG. 4 is a circuit diagram of a drive circuit according to a conventional example.

FIG. 5 is a graph illustrating a starting time of a drive circuit of a servo motor.

[Explanation of symbols]

 (11A) Latch circuit (11B) Latch circuit (12) Comparator (13) U / D pulse generation circuit (14) U / D counter (15) PWM circuit (16) Pre-driver (17) Multiplier circuit (18) Serial / Parallel conversion circuit (20) Drive control unit (21) Speed detection unit (22) Abnormal rotation detection circuit (23) Overcurrent detection circuit (M) Servo motor (S11 to S14) Switching transistor (DD) Target speed data (KD) Speed detection data (T0, T1) Startup time setting 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. The drive circuit is characterized in that the drive control unit changes a start time which is a time until the servomotor reaches a target rotation speed based on start time setting data which is digital data. 2. The drive control unit includes a comparator that compares the target speed data with the speed detection data, and a U / U that generates a pulse signal according to the output of the comparator.
D pulse generation circuit, up-down counter that counts the pulse signal, PWM circuit that generates a drive pulse whose duty ratio is determined based on the count result of the up-down counter, and switching of a switching transistor based on the drive pulse It has a pre-driver for driving and a switching transistor for driving the servo motor by supplying / not supplying current to the servo motor, and the speed detecting unit has an encoder circuit for detecting the rotation speed of the servo motor. The drive circuit according to claim 1, wherein the pulse generation circuit determines the frequency of the pulse signal based on the start-up time setting data.