JP3329142B2 - Position detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting circuit suitable for controlling a servomotor.

[0002]

2. Description of the Related Art Conventionally, position control of a load by a servomotor is performed by detecting the position or rotation angle of the load. FIG. 4 shows a conventional servo motor driving mechanism. In this figure, reference numeral 20 denotes a servomotor which controls the position of a table 23 as a load. Also,
Reference numeral 20a denotes a drive shaft of the servo motor 20. Reference numeral 1 denotes an incremental encoder which is a component of the servomotor 20, and outputs a pulse signal at equal angular intervals according to the rotation of the drive shaft 20a. Reference numeral 21 denotes a drive gear having P teeth (P is an integer), which is attached to the drive shaft 20a.

Reference numeral 22 denotes a driven gear having Q teeth (Q is an integer).
Engage with 1. Therefore, the rotation of the drive shaft 20 a of the servo motor 20 is transmitted to the table 23 via the drive gear 21 and the driven gear 22. The gear ratio at this time is Q / P. Reference numeral 24 denotes a sensor, and a table 23
And outputs a detection signal when the marker is detected.

In the above-described servo motor driving mechanism, the speed control of the servo motor 20 and the table 23 are performed based on the pulse signal output from the incremental encoder 1 and the position detection signal output from the sensor 24.
Position control. Some drive mechanisms of this type include an absolute encoder 25 that outputs a rotation angle as an absolute value to a rotation shaft of a table 23 instead of the sensor 24. In such a drive mechanism, the angle information output from the absolute encoder 25 is used as the absolute position information of the table 23, and the position of the table 23 is controlled based on this.

[0005]

By the way, the sensor 24
In the drive mechanism of the servo motor that performs the position control of the table 23 based on the position detection signal output from the controller 23, the position detection accuracy of the table 23 is low, and when it is necessary to detect a plurality of positions, the sensor Must be increased, and there are problems such as an increase in cost and a mounting position of the sensor.

In a servomotor drive mechanism using an absolute encoder 25 instead of the sensor 24, the absolute encoder itself is expensive,
In addition, there is a problem that the absolute encoder cannot be attached to the rotating shaft on the load side due to the installation position of the drive mechanism.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a position detecting circuit which enables highly accurate position detection with an inexpensive configuration.

[0008]

According to the first aspect of the present invention,
An angle information output means for sequentially outputting angle information of the motor in accordance with the rotation of the motor, and a position detection circuit for detecting a predetermined position of a load rotationally controlled by the motor via a predetermined gear ratio; Change amount detecting means for detecting a change amount between the motor angle information and the previously input motor angle information; and a change amount for converting the change amount output by the change amount detecting means into the load angle change amount. Based on the load angle change amount output from the change amount conversion unit and the load angle information obtained last time, the load angle information corresponding to the motor angle information input this time. Load angle output means for outputting, load processing means for outputting angle information of the load output from the load angle output means in accordance with a preset cycle, and the periodic processing means A position detecting circuit, characterized by comprising a position detecting means for detecting a predetermined position of the load based on the angle information of al the outputted loads.

According to a second aspect of the present invention, the predetermined position detecting means receives in advance angle information of a load corresponding to the predetermined position, and outputs the angle information of the motor sequentially outputted and the periodic processing means. Detection angle conversion means for making the load angle information corresponding to the predetermined position correspond to the motor angle information, based on the load angle information, and motor angle information output from the detection angle conversion means, 2. A position detection signal output means for comparing the angle information of the motor sequentially output from said angle information output means and outputting a position detection signal when both the angle information match. It is a position detection circuit of description.

According to a third aspect of the present invention, the detected angle conversion means obtains a difference between the load angle information corresponding to the predetermined position and the current load angle information output from the periodic processing means, A position of the load angle information corresponding to the predetermined position within a range between a minimum value and a maximum value of the load angle information output from the periodic processing means is determined, and the obtained difference is determined according to the position. Whether to add or subtract the value of the preset cycle or not to perform the addition / subtraction, convert the resulting value into angle information of the motor based on the gear ratio, and 3. The position detecting circuit according to claim 2, wherein the conversion result is added to the current angle information of the motor so that the angle information of the load corresponding to the predetermined position corresponds to the angle information of the motor.

According to a fourth aspect of the present invention, there is provided a load control device which is controlled in rotation through a predetermined gear ratio by a servomotor having a built-in incremental encoder which outputs a pulse signal at equal angular intervals in accordance with the rotation of the drive shaft. In a position detection circuit that detects a predetermined position, a counter that sequentially counts and outputs pulse signals output from the incremental encoder, a count value output from the counter,
A frequency divider that outputs load angle information corresponding to the angle of the load rotated by the servomotor based on the gear ratio in accordance with a preset cycle, and a total that is sequentially output from the counter. Numerical values and, based on the load angle information output from the frequency divider, convert angle information corresponding to a predetermined position of a preset load according to the count value sequentially output from the counter, A command generator that outputs angle information of the predetermined position according to the count value as detection command information, and compares a value of the detection command information output from the command generator with a count value sequentially output from the counter. And a comparator that outputs a position detection signal when the value becomes the same value.

[0012]

In the position detecting circuit according to the first aspect of the present invention, the amount of change in the angle information of the motor is obtained, and the obtained amount is converted into the change in the angle of the load. Load angle information corresponding to the amount of change in the angle of the motor is obtained, and the obtained load angle information is output in accordance with a preset cycle. Therefore, the load angle information can be generated at an arbitrary cycle. Therefore, not only can a predetermined position of the load be detected without directly detecting the position or angle on the load side, but also angle information of the load can be generated at a desired cycle.

In the position detecting circuit according to the present invention, the angle information corresponding to the predetermined position of the load is made to correspond to the angle information of the motor, and the angle information of the motor corresponding to the predetermined position of the load is sequentially output. A position detection signal is output based on the motor angle information. Accordingly, since the determination of the predetermined position in the load is performed based on the angle information of the motor that is the basis of the angle information of the load, accurate position detection can be performed.

According to a third aspect of the present invention, a position detection circuit determines a position of load angle information corresponding to a predetermined position within an output range of the load angle information sequentially output,
According to the determined position, a value of a preset cycle is added to or subtracted from the difference between the load angle information corresponding to the predetermined position and the load angle information sequentially output, or the addition / subtraction is not performed. Then, the result is converted into motor angle information and then added to the current motor angle information, whereby the load angle information corresponding to the predetermined position is made to correspond to the motor angle information. This makes it possible to accurately associate the load angle information corresponding to the predetermined position with the motor angle information wherever the load angle information corresponding to the predetermined position is within the output range of the load angle information. Becomes

According to a fourth aspect of the present invention, a position detecting circuit counts pulses sequentially output from an incremental encoder built in a servomotor, determines a rotation angle of the load based on the counted value, and calculates the rotation angle of the determined load. The angle information corresponding to the predetermined position of the load is converted based on the rotation angle and the count value in accordance with the angle information of the motor, is compared with the count value, and outputs a position detection signal when they match. Therefore, highly accurate position detection can be performed with an inexpensive configuration.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating the configuration of the position detection circuit according to the present embodiment. Further, the position detection circuit in the present embodiment will be described as being applied to the servomotor drive mechanism (excluding the sensor 24 and the absolute encoder 25) shown in FIG.

In FIG. 1, reference numeral 1 denotes an incremental encoder (pulse generator), which outputs a pulse signal at equal angular intervals in accordance with the rotation of the drive shaft 20a of the servo motor, as described above. Here, the drive shaft 20a is 1
A pulse signal is output each time the motor rotates. Reference numeral 2 denotes a counter, which counts the pulses output from the incremental encoder 1 and counts this count value on the drive shaft 2.
0a angle information (hereinafter referred to as drive shaft angle information) θ
Output as _m (k).

Here, it is assumed that a 16-bit binary counter is used as the counter 2 in the present embodiment. Therefore, the drive shaft angle information is sequentially output in the range of 0000 to FFFF, and the drive shaft has rotated once each time it is counted up by one.

Reference numeral 3 denotes a frequency divider (angle information conversion means).
The count value output from the counter 2 is
, The number of teeth Q of the driven gear 22 (where P <Q), and the total number of angle detection points T per rotation of the table 23
(Hereinafter referred to as period T), the number of points corresponding to the rotation of the table 23 is counted.
3 (hereinafter referred to as load angle information) θ _L (k)
Output as

In this embodiment, the number of teeth P of the driving gear 21 is set to 10, and the number of teeth Q of the driven gear 22 is set to 100, so that the gear ratio is 10. Also, the total number T of angle detection points per rotation of the table 23 is set to 360, and the frequency divider 3 outputs numerical values from 0 to 359 as load angle information θ _L (k) according to the rotation angle of the table 23. And

Reference numeral 4 denotes a command generator, which represents detected position information θ _L ^* and load angle information θ representing the detected position of the table 23 in correspondence with the value (fixed value) corresponding to the output value of the frequency divider 3.
_L (k), gear ratio P / Q, and drive shaft angle information θ
based on the _m (k), the detected position information of the drive shaft 20a side corresponding to the detected position information theta _L ^* (hereinafter referred to as the drive-side position detection information) to the theta _m ^* a (k).

That is, when the detected position of the table 23 is determined to be a position rotated by 90 ° from the origin, in this embodiment, the detected position information θ _L ^* is 90, and the command generator 4
Since the detected position information θ _L ^* is made to correspond to the drive shaft angle information, the drive-side position detected information θ _m ^* (k) changes to 1194, 1FA4, 2DB4,. Go.

Further, θ ₀ input to the command generator 4 is:
This is a value required when the detected position information θ _L ^{* is associated} with the drive shaft angle information, which will be described in detail later.

Reference numeral 5 denotes a comparator, which is used to detect drive-side position detection information θ.
_m ^* (k) is compared with the drive shaft angle information θ _m (k), and when both values are equal, a position detection signal is output. 6
Is a switch, which is turned off when an output prohibition signal (described later) is output from the command generator 4, and forcibly turns off the position detection signal output from the comparator 5.

Next, the configuration of the frequency divider 3 of the above-described position detection circuit will be described with reference to FIG. In FIG.
Reference numeral 10 denotes a memory, which is the drive-side position information θ input previously.
_m (k-1) is stored. A subtractor 11 outputs a difference Δθ _m (k) between the input drive axis angle information θ _m (k) and the previously input drive axis angle information θ _m (k−1). Further, for example, the counter 2 has a full count value (FFF).
When the count is incremented from 0000 to 0000, the subtractor 1
1 outputs the difference from the previous value (FFFF) as 1.

Reference numeral 12 denotes an electronic gear. A gear ratio is obtained from the number of teeth P of the driving gear 21 and the number of teeth Q of the driven gear 22 which are input from the outside, and based on this, the difference Δθ _m output from the subtractor 11 is obtained. Angle change Δθ of load corresponding to (k)
Output _L (k). Therefore, the angle change Δ of the load
θ _L (k) is as follows: Δθ _L (k) = P / Q · Δθ m (k) In this embodiment, the gear ratio is 10, and the counter 2 counts up each time the drive shaft 20a makes one rotation. Therefore, if the difference Δθ _m (k) is 10, the electronic gear 12 will rotate the load. 1 is output as the change amount Δθ _L (k).

Reference numeral 13 denotes an adder, which stores a load angle change Δθ _L (k) output from the electronic gear 12 into a memory 15.
Is added to the previous load-side position information θ _L (k−1), and the position information θ (k) is output. Reference numeral 14 denotes a periodic function generator, which outputs position information θ output from the adder 13.
(K) is adjusted so as to be output in the cycle T, and output as load angle information θ _L (k). For example, in the case of this embodiment,
The position information θ (k) is 359 based on the addition result of the adder 13.
Is exceeded, the load angle information θ _L (k) is adjusted to be output again from 0 in accordance with the exceeded value.

The operation of the above-described position detection circuit will be described below with reference to FIGS. Here, FIG. 3 is a graph showing the relationship between each count value output from the counter 2 and the frequency divider 3. First, when the position detection circuit of the present embodiment is started, a reset signal is supplied to the counter 2 and the frequency divider 3, and the respective count values are set to zero.
Thereby, each origin of the drive shaft 20a and the table 23 is set. The reset signal is transmitted to the memories 10, 1
5 to clear the stored contents of each memory.

Next, when the servo motor 20 rotates and a pulse signal is output from the incremental encoder 1 in response to the rotation, the pulse signal is counted by the counter 2 and the frequency is divided as drive shaft angle information θ _m (k). Output to the device 3. Then, the frequency divider 3 converts the drive shaft angle information θ _m (k) into load angle information θ _L (k) and outputs it by performing the following processing.

In FIG. 2, first, drive shaft angle information θ _m
When (k) is input to the frequency divider 3, the subtracter 11 calculates a difference from the previously input drive shaft angle information θ _m (k−1), and the drive shaft angle change Δθ _m ( k) is calculated. Further, the memory 10 stores the previous drive shaft angle information θ _m
After outputting (k-1), the drive shaft angle information θ input this time
_m (k) is stored. Next, in the electronic gear 12, the angle change amount Δθ _m (k) of the drive shaft is converted into the position change amount Δθ _L (k) of the table 23, and the load angle information θ _L (k) previously output by the adder 13. -1) is added.

As a result, position information θ (k) is obtained, and the position information θ (k) is output to the periodic function generator 14. The periodic function generator 14 performs the following condition processing on the position information θ (k) based on the value of the period T set from the outside. That is, when the position information θ (k) is larger than T−1, θ
(K) -T is output as load angle information θ _L (k). When the position information θ (k) is smaller than 0, θ (k) +
T is output as load angle information θ _L (k). When the position information θ (k) is equal to or more than 0 and equal to or less than T−1, θ (k) is directly output as load angle information θ _L (k).

Next, the command generator 4 receives an external input based on the load angle information θ _L (k) output from the frequency divider 3 and the drive shaft angle information θ _m (k) output from the counter 2. Detected position information θ _L ^*
Convert to _m ^* (k). Hereinafter, the procedure will be described with reference to FIG.

First, prior to the above-described conversion, in order to set a certain range for the detected position information θ _L ^* as an initial setting, range information θo (where θo <T /
The following condition processing is performed based on 2) to calculate the upper limit value θ _P ^* and the lower limit value θ _N ^* of the above range. If θ _L ^* + θo is larger than T-1, the upper limit value theta _P ^* and θ _L ^* + θo-T. Further, if θ _L ^* + θo is T-1 or less, the upper limit theta _P and θ _L ^* + θo. If θ _L ^* −θo is smaller than 0, the lower limit θ _{N is set} to θ _L ^* −.
θo + T. When θ _L ^* −θo is 0 or more, the lower limit value θ _N ^{* is set} to θ _L ^* −θo.

The setting of the range based on the upper limit value θ _P ^* and the lower limit value θ _N ^* obtained by the above-described condition determination depends on the positional relationship of the detected position with respect to the origin of the table 23 and the period T.
_It is required to convert _L ^* to θ _m ^* (k). And
After this initial setting, the following condition processing is further performed to convert θ _L ^* into θ _m ^* (k).

Θ _N ^* <θ _P ^* and θ _N ^* <θ _L (k) <
When ^{_{θ P *, θ m * =}} θ m (k) + (P / Q) {θ L * -θ L (k)} θ N *> θ P *, ^{_{and, T / 2 <θ L *}} , And θ _N ^* <θ _L
(K) ^{_{When, θ m * = θ m (}} k) + (P / Q) {θ L * -θ L (k)} θ N *> θ P *, ^{_{and, T / 2 <θ L *}} , And θ _P ^* > θ _L
(K) ^{_{When, θ m * = θ m (}} k) + (P / Q) {θ L * -θ L (k) -T} θ N *> θ P *, and, T / 2> θ _L ^{* And} θ _N ^* <θ _L
(K) ^{_{When, θ m * = θ m (}} k) + (P / Q) {θ L * -θ L (k) + T} θ N *> θ P *, and, T / 2> θ _L ^* And θ _P ^* > θ _L
In the case of (k), θ _m ^* = θ _m (k) + (P / Q) {θ _L ^* −θ _L (k)} In addition, if none of the above-mentioned conditions is satisfied, θ _m ^* Outputs the output stop signal without changing the previous value.

For example, when the above-mentioned values have the relationship shown in FIG. 3, the above-mentioned conditions are satisfied, and therefore, the drive-side position detection information θ _m ^* (k) becomes
A value obtained by subtracting the load angle information from the detected position information and multiplying the result by the reciprocal of the gear ratio is added to the drive shaft angle information output from the counter 2.

The drive-side position detection information θ _m ^* (k) output from the command generator 4 is output to the comparator 5 by drive-axis angle information θ.
_The position detection signal is output when the value is compared with _m (k) and becomes the same value. When the output prohibition signal is not output from the command generator 4 in the switch 6, the switch 6 is turned on, and the position detection signal is output from the comparator 5 to the outside.

As the counter 2, a counter that counts up when the servo motor rotates forward and counts down when the servo motor rotates reversely is used.
In the forward rotation, the rotation change amount Δθ of the positive sign load
Outputs _L (k), if at the time of reverse rotation by using the outputs a rotational change amount [Delta] [theta] _L of the load minus sign (k), to constitute a position detecting circuit capable of detecting the position of the desired load even during reverse rotation Can be.

As described above, the position detection circuit according to the present embodiment is indispensable for the control of the servomotor, and based on the pulse signal output from the incremental encoder normally incorporated in the servomotor, the desired load is detected. Since the position is detected, inexpensive and highly accurate position detection becomes possible.

[0040]

As described above, according to the first aspect of the present invention, in the position detection circuit for detecting the predetermined position of the load whose rotation is controlled by the motor via the predetermined gear ratio, the rotation of the motor is controlled. Angle information output means for sequentially outputting the angle information of the motor in accordance with, a change amount detection means for detecting a change amount between the currently input angle information of the motor and the previously input angle information of the motor, A change amount conversion means for converting a change amount output from the change amount detection means into an angle change amount of the load; an angle change amount of the load output from the change amount conversion means; and a load angle obtained last time. Load angle output means for outputting angle information of the load with respect to the angle information of the motor input this time, based on the information,
The load angle information output from the load angle output means is:
Since there are provided periodic processing means for processing so as to be output in accordance with a preset cycle, and predetermined position detecting means for detecting a predetermined position of the load based on angle information of the load output from the periodic processing means, Not only can a predetermined position of the load be detected without directly detecting the position or angle on the load side, but also the angle information of the load can be generated at a desired cycle, whereby the servomotor drive mechanism The degree of freedom regarding the installation of the equipment is improved.

According to the second aspect of the present invention, the predetermined position detecting means receives the angle information of the load corresponding to the predetermined position in advance, and outputs the angular information of the motor sequentially outputted and the periodic processing means. Based on the output load angle information, the load angle information corresponding to the predetermined position,
Detection angle conversion means corresponding to the angle information of the motor, angle information of the motor output from the detection angle conversion means,
A position detection signal output unit that compares the angle information of the motor sequentially output from the angle information output unit and outputs a position detection signal when both of the angle information match, so that the determination of the predetermined position in the load is performed. Is performed based on the angle information of the motor which is the basis of the angle information of the load, so that accurate position detection can be performed.

According to the third aspect of the present invention, the detected angle conversion means obtains a difference between the load angle information corresponding to the predetermined position and the current load angle information output from the periodic processing means. At the same time, the position of the load angle information corresponding to the predetermined position within the range between the minimum value and the maximum value of the load angle information output from the periodic processing means is determined, and the position is determined according to the position. Whether to add or subtract the value of the preset cycle to the difference or not to perform the addition / subtraction, convert the resulting value into angle information of the motor based on the gear ratio. By adding the conversion result to the current angle information of the motor, the angle information of the load corresponding to the predetermined position is made to correspond to the angle information of the motor, so that the angle information of the load corresponding to the predetermined position is negative. Even anywhere within the output range of the angular information, it becomes possible to accurately correspond to the load angle information the angle information of the motor corresponding to the predetermined position.

According to the present invention, the rotation is controlled via a predetermined gear ratio by a servomotor having a built-in incremental encoder which outputs a pulse signal at equal angular intervals in accordance with the rotation of the drive shaft. In a position detection circuit that detects a predetermined position of the load, a counter that sequentially counts and outputs pulse signals output from the incremental encoder, based on a count value output from the counter, and the gear ratio, A frequency divider that outputs load angle information corresponding to the load angle rotated by the servomotor according to a preset cycle, a count value sequentially output from the counter, and an output from the frequency divider Based on the load angle information to be performed, the angle information corresponding to the predetermined position of the load set in advance, sequentially from the counter Converted in accordance with the force is the count value,
A command generator that outputs angle information of the predetermined position according to the count value as detection command information, and compares a value of the detection command information output from the command generator with a count value sequentially output from the counter. However, since it has a comparator that outputs a position detection signal when the value becomes the same, not only can it perform high-precision position detection with an inexpensive configuration, but also directly install a sensor or absolute encoder, etc. Since there is no need to detect the position or angle of the load, the degree of freedom regarding the installation of the drive mechanism of the servomotor is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a position detection circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a measurement counter of the position detection circuit.

FIG. 3 is a graph for explaining a configuration of a position detection circuit according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining a configuration of a conventional servo motor driving mechanism.

[Explanation of symbols]

1 ... incremental encoder, 2 ... counter,
3 ... frequency divider, 4 ... command generator, 5 ... comparator, 6 ... switch, 10, 15 ... memory, 11 ...
Subtractor, 12 Electronic gear, 13 Adder, 14
Periodic function generator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01D 5/00-5/62 G01B 7/00-7/34 G01B 11/00-11/30 G01P 1 / 00-3/80

Claims (4)

(57) [Claims] 1. A position detecting circuit for detecting a predetermined position of a load rotationally controlled by a motor via a predetermined gear ratio, wherein the angle information output means sequentially outputs angle information of the motor in accordance with the rotation of the motor. A change amount detecting means for detecting a change amount between the motor angle information inputted this time and the motor angle information inputted last time; and a change amount outputted by the change amount detecting means as the angle change of the load. A change amount conversion means for converting the angle information of the load, the angle change amount of the load output from the change amount conversion means, and the angle information of the motor input this time based on the angle information of the load obtained last time. Load angle output means for outputting load angle information; load angle information output from the load angle output means;
A periodic processing means for performing processing so as to be output according to a preset cycle; and a predetermined position detecting means for detecting a predetermined position of the load based on angle information of the load output from the periodic processing means. Characteristic position detection circuit. 2. The method according to claim 1, wherein the predetermined position detection unit receives, in advance, load angle information corresponding to the predetermined position, and sequentially outputs the motor angle information and the load angle information output from the periodic processing unit. Based on the detected angle conversion means for making the angle information of the load corresponding to the predetermined position correspond to the angle information of the motor; the angle information of the motor output from the detected angle conversion means; and the angle information output means. 2. The position detection circuit according to claim 1, further comprising: a position detection signal output means for comparing the sequentially output angle information of the motor and outputting a position detection signal when both the angle information match. 3. The detection angle conversion means obtains a difference between the angle information of the load corresponding to the predetermined position and the current angle information of the load output from the periodic processing means, and calculates a difference corresponding to the predetermined position. Load angle information, determine the position within the range between the minimum value and the maximum value of the load angle information output from the periodic processing means,
Whether to add or subtract the value of the preset cycle to the determined difference according to the position, or to determine whether to perform the addition or subtraction, determine the resulting value based on the gear ratio. 3. The motor according to claim 2, wherein the angle information of the load corresponding to the predetermined position corresponds to the angle information of the motor by converting the angle information of the motor into the angle information of the motor and adding the conversion result to the angle information of the motor at the present time. The position detection circuit as described. 4. A position for detecting a predetermined position of a load whose rotation is controlled via a predetermined gear ratio by a servomotor having a built-in incremental encoder that outputs a pulse signal at equal angular intervals according to the rotation of the drive shaft. In the detection circuit, a counter that sequentially counts and outputs a pulse signal output from the incremental encoder; a count value output from the counter; and a gear ratio that is rotated by the servo motor based on the gear ratio. A frequency divider that outputs load angle information corresponding to the load angle in accordance with a preset cycle; a count value sequentially output from the counter; and a load angle information output from the frequency divider. The angle information corresponding to the predetermined position of the preset load is changed based on the count value sequentially output from the counter. In other words, a command generator that outputs angle information of the predetermined position according to the count value as detection command information, a value of the detection command information output from the command generator, and a total output sequentially from the counter. And a comparator for comparing a numerical value and outputting a position detection signal when the value becomes the same.