JPH06201310A - Position detector - Google Patents

Abstract

(57) [Summary] [Purpose] The resolution can be changed according to the stroke amount to be measured, and digital position signals and analog position signals can be selectively used. [Structure] A pair of magnetic sensors 5 that outputs a two-phase sine wave signal having a phase difference of 90 ° corresponding to the pitch of the magnetic scale 3, and the peak value of each sensor output for each pitch of the magnetic scale 3. A means 53 for updating / storing, a means 54 for calculating a center value for each pitch from each peak value, a means 55 for calculating a rough position based on the comparison result of the center value and the sensor output, and a peak value. A means 56 for calculating the normalization coefficient of the sensor output from the center value, a means 57 for correcting the sensor output based on the normalization coefficient, and an accurate trigonometric function inverse operation using the two-phase corrected normalization signals. It is provided with means 58 for calculating the position, means 59 for outputting the position signal by adding the coarse position and the fine position, means 51 for switching the resolution of the position signal, and digital / analog conversion means 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a device for detecting the stroke position of an actuator such as a rod of a hydraulic cylinder with high accuracy.

[0002]

2. Description of the Related Art As a device for detecting the stroke position of a piston rod of a hydraulic cylinder, a magnetic scale having weak magnetic portions arranged at regular intervals in the axial direction of the surface of the piston rod is constructed. A relative position detection type is known in which the detection signal of the sensor changes in a sinusoidal waveform due to the displacement of the piston rod to detect the position with high resolution from the incremental value of the displacement. Japanese Patent Application Laid-Open No. 4-136713 proposes a device capable of highly accurate measurement.

[0003]

However, since the above-mentioned conventional apparatus has a fixed resolution, it may be necessary to make drastic changes when applied to a plurality of actuators having different stroke amounts. Since the position signal and the digital position signal cannot be selectively output, a problem may occur in a servo system or the like that requires an analog position signal for feedback.

Therefore, it is an object of the present invention to provide a position detecting device which can change the resolution to be measured and can selectively use a digital position signal and an analog position signal.

[0005]

According to the present invention, in FIG. 1, a magnetic scale 3 in which weak magnetic portions are arranged at a predetermined pitch in the moving direction and a pitch of the magnetic scale 3 corresponding to 90
A pair of magnetic sensors 5 that output two-phase sine wave signals having a phase difference of °, means 53 that updates and stores the peak value of each sensor output for each pitch of the magnetic scale 3, and each peak value. Means 54 for calculating the center value for each pitch
A means 55 for calculating a rough position based on the comparison result of the center value and the sensor output; a means 56 for calculating a normalization coefficient of the sensor output from the peak value and the center value; Means 57 for correcting the sensor output based on
In a position detecting device comprising means 58 for calculating a fine position by trigonometric function inverse calculation using a phase-corrected normalized signal, and means 59 for adding a coarse position and a fine position and outputting a position signal. Means for switching the resolution of the position signal, and converting the digital position signal into an analog position signal,
And means 52 for outputting.

[0006]

Therefore, the peak value of the sensor output is updated and stored in the storing means for each pitch, and the reciprocal of the difference between the peak value and the center value at each pitch is determined as the normalization coefficient. By multiplying the sensor output by this normalization coefficient, the sensor output is corrected for each pitch of the magnetic scale, the respective amplitude levels are equalized, and the precise position is calculated by the normalized two-phase signal, and each sensor is calculated. The coarse position is calculated based on the result of comparison between the output and the center value, and the fine position and the coarse position are added together to output the position signal. The position signal is converted into a measurement unit selected by the resolution switching means and output as a digital position signal, and the converted digital position signal is output as an analog position signal by the digital / analog converting means.

[0007]

EXAMPLES Examples of the present invention are shown in FIGS.

In FIG. 2, reference numeral 1 denotes a piston rod made of a magnetic material (ferromagnetic portion) which constitutes a hydraulic cylinder (not shown), and the surface of the piston rod 1 has a predetermined depth P with a predetermined pitch P in the axial direction. A weak magnetic portion 2 is provided to form a magnetic scale 3.

The weak magnetic portion 2 and the ferromagnetic portion 4 of the magnetic scale 3 are both provided with a width of P / 2 and are arranged at a pitch P.

At one end of a hydraulic cylinder (not shown), a pair of sine wave signals of two phases having a phase difference of 90 ° with one pitch of the magnetic scale 3 as one cycle according to the displacement of the piston rod 1 are output. A magnetic sensor 5 is provided.

Two-phase output signal sigA from the magnetic sensor 5
(Phase A below) and sigB (Phase B below) are input to the controller 7 configured by a microcomputer as shown in FIG. 3, and the relative position of the stroke of the piston rod 1 is calculated based on this. . The calculation of the relative position is performed by, for example, a predetermined number of 1/2 pitches based on the normalization coefficient obtained based on the peak values (maximum value and minimum value) of the output signals A and B of the magnetic sensor 5, for example 1/10
The position (fine position) divided into 0 mm) is obtained, and the respective center values obtained based on the respective peak values of the output signals A and B phases are compared with the output signals A and B phases. / 2
The relative position of the stroke is obtained by obtaining the position (coarse position) in pitch units and summing these.

The output signals A and B of the magnetic sensor 5 are input to the central processing unit CPU of the controller 7 via the sample and hold circuits SHA and SHB and the analog / digital converter ADC.

The comparators CA and CB output signals A and B with the central value, which is the median between the maximum and minimum values of the output signals A and B phases of the magnetic sensor 5 calculated by the CPU, as the reference value. Compared with the phase, an H level signal is output when it is larger than the center value, and an L level signal is output when it is smaller than the center value. It should be noted that DACA and DACB are digital-analog converters that perform analog conversion of each center value calculated by the CPU.

The digital position signal output from the controller 7 is output via the resolution switching circuit 9. A switch 8 for setting the resolution is connected to the resolution switching circuit 9, and this switch 8 is, for example, ₃ of SW _{1 to} SW 3.
It is composed of two switches, and the set value of the resolution is input to the resolution switching circuit 9 as a 3-bit digital position signal by turning on and off these SW _{1 to} SW ₃ .

The resolution switching circuit 9 is composed of, for example, a shift register as shown in FIG. This shift register is made up of 16 bits. The upper 8 bits are the upper byte, the lower 8 bits are the lower byte, and the most significant bit of the upper byte is the sign part that indicates whether the data is positive or negative. In this shift register, the number of right shifts is determined according to the states of SW ₁ to SW ₃ of the switch 8, and the resolution is 1/100.
~ 16 / 100mm, measuring stroke is ± 75 to ± 120
It is changed between 0mm.

In the present embodiment, the 14-bit D / A converter is used in bipolar, and the data range is about ± 8192. When the effective range is up to ± 7500, the measurement stroke is ± 75.00 mm when the resolution is 1/100 mm.

The resolution switching circuit 9 outputs a digital position signal having the resolution set by the switch 8, and the digital-analog converter 1 connected to the resolution switching circuit 9 is outputted.
An analog position signal obtained by converting the digital position signal is output from 0.

A peak value for each pitch of the output signals A and B of the magnetic sensor 5 is stored in the memory RAM. As shown in FIG. 5, the sensor signals A and B phases that are sequentially updated and stored in the memory RAM are divided into A phase and B phase, and the peak values (maximum value and minimum value) of the stored peak values are stored. A class value indicating the content (reliability) is stored.

An actual measured value is stored by deciding the position of the memory RAM so that the maximum value is an even number and the minimum value is an odd number. However, the expected value is set at the initial setting. Then, the class value is represented as three kinds of weighting factors, as will be described later, depending on the content of the stored peak value.

The position calculation and resolution switching operation will now be described with reference to the flow charts of FIGS.

First, the flowcharts of FIGS. 6 and 7 are executed when the sensor signal A (A-phase sensor signal) and the sensor signal B (B-phase sensor signal) cross the center value, respectively. When it is determined that the output of the comparator CA has changed and the A-phase sensor signal crosses the center value, the peak value hold mode of the B-phase sensor signal is simultaneously switched. (S1-2) As shown in FIG. 5, when the A-phase sensor signal crosses the center value, the B-phase sensor signal takes the maximum value or the minimum value. deep.

When the A-phase sensor signal crosses the center value, the coarse position of the magnetic scale 3 in 1/2 pitch units is obtained, and at that time, the output values of both comparators CA and CB are high level or low level. The stroke direction is determined by whether or not there is a match, and when they match, the A-phase coarse position counter is counted down, and when they do not match, the count is increased.

The A-phase sensor signal and the B-phase sensor signal are 90
Although there is a phase difference of ゜, the stroke direction in which the phase of the A phase is advanced by 90 ° relative to the phase of the B phase is assumed to be the positive direction, because the phases of the piston rod 1 advance or delay depending on the moving direction of the piston rod 1. Then, as shown in FIG. 5, the output of the comparator immediately after the phase A crosses the center value is always B
It is different from the phase comparator output. Therefore, the A-phase coarse position counter is incremented when the stroke is in the positive direction, and is decremented when not.

Here, the A-phase coarse position counter and B described later
The phase coarse position counter is preliminarily set in advance so that the A phase coarse position counter value-the B phase coarse position counter value becomes 0 or 1, and the coarse position counter is obtained by obtaining the difference between both counter values in S6. You can check for errors.

In other words, when the coarse position counter malfunctions due to disconnection of the sensor signal line, excessive noise, or a decrease in the output of the comparator, and the difference between the two counters is no longer 0 or 1, an abnormality can be immediately determined, and S7
Outputs an error.

Next, in S8, from the A phase peak value and the center value,
The normalization coefficient of the A-phase sensor signal is calculated. This normalization coefficient is a coefficient for correcting the difference in the amplitude of the sensor output for each pitch of the magnetic scale 1 and adjusting it to the same level, and is used in the normalization processing when calculating the precise position.

This normalization coefficient Asc is 1 / | peak value A
pe-center value Ace | The values obtained from the flowchart of FIG. 7 are used as the A-phase peak value and the center value.

Assuming that the normal value of | peak value Ape-center value Ace | is 1 and the measured value is twice as large,
In this case, the normalization coefficient is ½, and the normalization coefficient is multiplied by the amplitude of the A-phase sensor signal by the normalization coefficient to be described later, so that the amplitude value is corrected to 1 and the amplitude of each pitch is corrected. Can be replaced at the same level as the regular one.

Next, the peak value of the B-phase sensor signal which has been previously held is updated (S9). This update process is performed according to the flowchart of FIG. 8 described later.

In S10, it is determined whether it is time to calculate the B-phase center value, and if the sensor signal is at the peak value, the center value is calculated (S11).

The center value is calculated as an intermediate value between the latest maximum value and the minimum value within the same pitch which is going forward depending on the stroke direction, but the center value itself does not change greatly. Alternatively, it can be calculated as an average value of the maximum value and the minimum value between several pitches before and after.

This calculation result is output as a B-phase center value for rough position calculation and for ensuring its position detection accuracy (S1).
2).

The processing when the B-phase sensor signal of FIG. 7 crosses the center value is the same as the above-described processing when the center value of the A-phase sensor signal is crossed, but the processing is up to the opposite phase. The downcount decision is reversed. As shown in FIG. 5, when the B-phase sensor signal crosses the center value, the A-phase sensor signal takes a peak value. Therefore, the A-phase peak value update and the center value are performed in the same manner as above. Is calculated, and the normalization coefficient of the B-phase sensor signal is calculated (S1 ′ to 12 ′). Next, the peak value of FIG. 8 is updated by crossing the center values of the A-phase and B-phase sensor signals. At times, the phases are opposite to each other, and the peak value of the sensor signal subjected to the peak hold at the crossing of the center values is captured, and then the class check of the peak value already stored at that position is performed (S21, Two
2).

Then, the weighting factors Gu, Es, Me set for each class are selected, and the updated peak value is calculated based on these factors (S23-26).

In this calculation, the peak value already stored is multiplied by the selected coefficient, and the peak value currently fetched is multiplied by the reference coefficient Te, which is added, and this is added to the reference coefficient and the selection coefficient. It is performed by dividing by the value obtained by adding and. As described above, when Me = 1, the selection coefficient has a relation of Me>Es> Gu, and Te is usually 1. Further, this reference coefficient may be (1 / update number) according to the number of updates, or may be Te> 1 in order to prioritize the peak value currently fetched.

The peak value is updated by taking into account signal acquisition errors and the like, and even in the initial stage when the actual measurement value is not stored, the weighting coefficient that differs depending on the class is used in order to improve the accuracy of the calculation result by approaching the expected value as early as possible. The value corrected using is averaged with the current peak value and stored as an updated peak value.

Further, two positions ahead of the position where the current peak value is stored in S28 to 33 and two positions before (the peak value corresponds to the maximum value, it corresponds to the maximum value storage position of the peak values before and after it. If the peak value class of) is the earliest estimated value, the current updated peak value is stored, the class is rewritten to a rough value, and thus stored before and after based on the actual measured value up to the present. Bring the peak value as an expected value closer to the new value as soon as possible.

That is, if the estimated value, S28-30
Then, check the class of the peak value two places ahead and make an estimate of G
If it is u, the stored peak value is changed to the current peak value, the class is rewritten to an approximate value, and S31 to 33
Check the class of the peak value two before, and similarly change and rewrite if it is an estimated value.

As a result of checking the class in S28 and S31, when it is determined that the value is the approximate value or the actual value, the value is left as it is, and the peak value is not updated and the class is not rewritten.

Next, according to the flow chart of FIG. 9, the A-phase and B-phase sensor signals are normalized by using the center value, the peak value, the normalization coefficient, etc. obtained as described above, and the coarse position is determined. The precise position is obtained, and these are added together to calculate the stroke position.

First, the A and B phase sensor signals are sampled and held at the same time, and then A / D converted to obtain the sensor signals As and Bs.
(S41). In S42 and S43, the current phase values Ace and Bce and the normalization coefficients Asc and Bsc are used to normalize the sensor signals of the A phase and the B phase.

The normalized signal Aco of the A-phase sensor signal is obtained by subtracting the center value Ace from the sensor signal As and multiplying it by the above-mentioned normalization coefficient Asc, whereby the amplitude level at each pitch becomes the same level. Will be fixed.

The normalized signal Bco of the B-phase sensor signal Bs can be obtained in the same manner.

In S44, the composite amplitude of the normalized signal is obtained, and it is determined whether the normalized signal is correct. FIG. 13 shows the judgment area of the normal judgment. Since both sensor signals have a phase difference of 90 degrees, they are represented by sin θ and cos θ, and a predetermined width is normalized to the circle drawn by sin ² θ + cos ² θ = 1. It will be in a state. If the combined amplitude falls within this range, both the normalized signals Aco and Bco are judged to be correct, while if they fall outside this range, it is judged to be an error and an error signal is output.

The cause of this error is, for example, disconnection of the sensor signal line, excessive or insufficient sensor signal amplitude, and the like.

Next, the precise position is calculated based on the A and B normalized signals, and at the same time, the values of the A and B coarse position counters indicating the coarse position are selected.

First, in order to prevent the misalignment between the fine position and the rough position due to the influence of noise contained in the sensor signal, first, FIG.
Graph of the composite wave of the normalized signal Aco-Bco shown in (sin ² θ
+ Cos ² θ = 1), it is determined in which area the current position is divided by the 45 ° line in the figure. This 45 ° line is {(1/4, 3/4, 5/4, 7
/ 4) π} line. In the four areas divided by the 45 ° line, the coarse position counter of either phase changes,
By selecting the counter value of the area immediately before the area of the current position, a highly accurate rough position can be determined,
Further, the fine position and the coarse position can be matched.

Therefore, in S45, the area is determined from the magnitude of the absolute values of the normalized signals Aco and Bco, the rough position is selected, and the fine position is calculated by the trigonometric function inverse calculation described later.

When the normalized signal | Bco | is larger than | Aco | in S45, the B-phase coarse position counter is selected in S46 and the count value is set as the coarse position.

Conversely, when | Bco | is smaller than | Aco |, the A-phase coarse position counter is selected in S51.

The inverse trigonometric operation for calculating the precise position is shown in FIG.
As shown in 4, the A-phase sensor output is a sine wave (sin θ),
Assuming that the B-phase sensor output is a cosine wave (cos θ), the A-phase and B-phase sensor outputs y ₁ and y ₂ due to the movement of the piston rod 1 in one pitch (0 to 2π) of the magnetic scale 3 are expressed by the following equation. To be done.

Y ₁ = v ₁ sin θ y ₂ = v ₂ cos θ Here, v ₁ and v ₂ are peak voltage values based on the characteristics of the magnetic sensor 5 and the magnetic scale 3, so that v ₁ = v _2. When normalized using the above-mentioned normalization coefficient, tan θ = sin θ / cos θ = y ₁ / y ₂ is obtained. Therefore, the angle θ is obtained from the sensor outputs y ₁ and y ₂ by the following equation.

Θ = tan ^-1 (y ₁ / y ₂ ) The precise position F _D of the piston rod 1 at one pitch P (or 1/2 pitch P) is calculated by the following equation based on the above θ.

F _D = (P / 2π) × θ Here, one pitch P of the magnetic scale 3 is set to, for example, 2 mm (the coarse position is in units of 1 mm), and the coarse position interval is divided into 100 equal parts. If the unit quantity of position is 1 /
The precise position F _{D in} units of 100 mm is calculated by the following equation.

F _D = (100 / π) × tan ⁻¹ (| Aco | / | Bco |) The precise position thus calculated is determined in S48 as to whether the signs of the normalized sensor signals Aco and Bco are the same. To correct.

[0056] If the sign is a correction fine position S49 if differences of (50 + F _D), is calculated in S50 if they match code is a (50-F _D).

On the other hand, in S45, the normalized signal | Aco
If | is larger than | Bco |, proceed to S51 to 55,
Take the count value of the A-phase coarse position counter as the coarse position,
The precise position F _D is calculated by the following formula.

F _D = (100 / π) × tan ⁻¹ (| Bco | / | Aco |) On the other hand, when the signs match, S 55 sets F _D as the precise position, and when they do not match, −F in S 54 Output _D.

As shown in FIG. 12, the phase B sensor signal crosses the center value at 0 → π → 0 (2π), and the crossing position of the phase A sensor signal is 1 / 2π → 3 / 2π → 1 / 2π
Becomes

Here, the coarse position signal is 7 / 4π → 1/4
π, 3 / 4π → 5 / 4π, A phase coarse position counter,
It is only necessary to select the B-phase coarse position counters in the range of 1 / 4π → 3/4/4, 5 / 4π → 7 / 4π, and by adding the fine position to this in S56, a highly accurate position signal can be obtained. .

The digital position signal having a resolution of 1/100 mm thus obtained is input to the resolution switching circuit 9 and according to the flow charts shown in FIGS.
It is converted by the switch 8 into a digital position signal corresponding to a preset resolution.

10 to 11, in step S60, the state of the switch 8 is read, a predetermined numerical value is substituted for a variable SPAN for setting the resolution according to this state, and then conditional branching is performed. Setting numbers to the variables SPAN, as shown in FIG. 11, on the SW ₁ to SW ₃ in S61 to S64, it sets the value of 1 to 5 in S65~S69 to determine the off.

Then, in accordance with the value set in this SPAN, the process branches to S70 to 74, the data portion of the shift register of the resolution switching circuit 9 is sequentially shifted to the right as shown in FIG. The position signal thus obtained is set to the resolution and measurement stroke selected by the switch 8.

That is, in S70 where SPAN = 1, the shift is not executed, the resolution is set to 1/100 mm which is the maximum resolution of the position signal, and the measurement stroke is set to ± 75 mm. In S71 where SPAN = 2, the resolution is 2/100 m by shifting to the right by 1 bit (once).
m, the measurement stroke is ± 150 mm.

Hereinafter, S72 to S for SPAN = 3 to 5
At 74, the resolution is further shifted to the right 2 to 4 times to roughen the resolution to 4/100 to 16/100 mm, while expanding the measurement stroke to ± 300 to ± 1200 mm. FIG. 4 shows an example in which the right shift is executed twice, the resolution is 4/100 mm, and the measurement stroke is ± 300 mm.

In this way, the digital position signal converted to the predetermined resolution is output in S75, and further, S76 to S7.
At 9, processing for converting this digital position signal into an analog position signal is performed. That is, if the position signal is positive in S76, the sign portion of the shift register in FIG. 4 is set to 1 in S77, whereas if the position signal is negative, the digital position signal is inverted in S78 and then the sign portion is set to 0 in S79. Then
In S80, it is output to the digital / analog converter 10, and the digital / analog converter 10 outputs an analog position signal corresponding to the shift register of the resolution switching circuit 9.

In this way, by repeating the processing of the above flow chart, the rough position and the fine position are obtained based on the two-phase sensor outputs of the magnetic sensor 5, and then the current stroke position is calculated with high accuracy, and the switch is switched. It is possible to detect the resolution previously selected in step 8 and convert the position signal into a predetermined resolution, and it is possible to easily change the resolution at any time according to the stroke of the actuator or the purpose of use, and to obtain a predetermined resolution. The converted digital position signal can be converted into an analog position signal, and a control device or the like using analog feedback can be easily connected.

FIG. 15 shows another embodiment, in which the position signal calculated in the first embodiment is output as a speed signal by the differentiating circuit 60, and other configurations are the same as those in the first embodiment. Is. The resolution switching means 51 outputs a digital speed signal having a preset resolution, and the digital-analog conversion means 52 outputs an analog speed signal. In addition, the digital signal may be used as the position output, the analog signal may be used as the speed output, and the combination thereof may be arbitrarily performed.

Although the resolution is set by the switch 8 in the above embodiment, it may be set by communication from an external controller, which is not shown.

[0070] Further, in the above embodiment, a switch for setting the resolution was three and the Sw ₁ to SW _3, this number may be arbitrarily changed.

Further, in the above embodiment, the resolution of the digital position signal and the analog position signal was set by the switch 8. However, although not shown, it is also possible to provide resolution setting switches for each of the digital position signal and the analog position signal. Yes, this allows different resolutions.

[0072]

As described above, according to the present invention, the current position is calculated with high accuracy after obtaining the rough position and the fine position based on the output of the magnetic sensor, and the position signal is converted into the preset resolution. It is possible to change the resolution easily at any time according to the stroke of the actuator and the purpose of use, and it is also possible to convert the digital position signal converted to a predetermined resolution into an analog position signal. A control device or the like that uses feedback can be easily connected.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a magnetic scale showing an embodiment of the present invention.

FIG. 3 is a block diagram of a controller.

FIG. 4 is a diagram showing a main part of a resolution switching circuit.

FIG. 5 is a diagram showing changes in the output signal of the magnetic sensor at each pitch.

FIG. 6 is a flowchart for calculating a normalization coefficient and a center value of phase A.

FIG. 7 is a flowchart for similarly calculating a B-phase normalization coefficient and a center value.

FIG. 8 is a flowchart showing a peak value updating operation.

FIG. 9 is a flowchart of a calculation operation for obtaining a position signal from a fine position and a coarse position.

FIG. 10 is a flowchart showing a resolution setting operation.

FIG. 11 is a flowchart showing a resolution determination operation.

FIG. 12 is a diagram showing a relationship between a coarse position counter and a quadrant position in a combined amplitude of A phase and B phase.

FIG. 13 is an explanatory diagram of a composite amplitude, similarly.

FIG. 14 is an explanatory diagram of calculation of a stroke position.

FIG. 15 is a block diagram showing another embodiment.

[Explanation of symbols]

 1 piston rod 2 weak magnetic part 3 magnetic scale 4 ferromagnetic part 5 magnetic sensor 7 controller 8 switch 9 resolution switching circuit 10 D / A converter 51 resolution switching means 52 digital / analog conversion means 53 peak value updating / storing means 54 center Value calculation means 55 Coarse position calculation means 56 Normalization coefficient calculation means 57 Sensor output correction means 58 Fine position calculation means 59 Position signal calculation means 60 Differentiation circuit

Claims (1)

[Claims] 1. A magnetic scale in which weak magnetic portions are arranged at a predetermined pitch in the moving direction, and a pair of magnetics which output two-phase sine waves having a phase difference of 90 ° corresponding to the pitch of the magnetic scale. A sensor, a means for updating / storing each sensor output peak value for each pitch of the magnetic scale, a means for calculating a center value for each pitch from each peak value, and a comparison result of the center value and the sensor output. Means for calculating a rough position based on the above, a means for calculating a normalization coefficient of the sensor output from the peak value and the center value, a means for correcting the sensor output based on the normalization coefficient, and a two-phase correction In a position detection device comprising means for calculating a fine position by trigonometric inverse calculation using the normalized signal and means for outputting a position signal by adding a rough position and a fine position, Means for switching resolution And a unit for converting a digital position signal into an analog position signal and outputting the analog position signal.