JPH06201400A - Position detector - Google Patents

Abstract

(57) [Summary] [Purpose] A scale for detecting the relative position and the reference position is integrally formed to shorten the startup time. [Structure] A magnetic scale 2 having weak magnetic portions formed at a predetermined depth arranged at a predetermined pitch, and a weak magnetic portion corresponding to a predetermined reference position of the magnetic scale 2 having a depth corresponding to the reference position. The formed reference point, a magnetic sensor 5 that outputs a sine wave according to the pitch of the weak magnetic portion, a means 10 that calculates a relative position from the output of the magnetic sensor 5, a means 20 that also detects the reference point, and a reference. Means 2 for determining the amplitude level of a point
2 and means 24 for storing the absolute position corresponding to the reference point
And means 25 for determining the moving direction of the actuator 30.
And means 23 for controlling the absolute position signal of the storage means 24 based on the amplitude level of the reference point and the moving direction, and the absolute position is calculated from the absolute position of the reference point read by the absolute position signal control means 23 and the relative position. Means 21 for doing so.

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.

In these relative position detecting type position detecting devices, a limit switch is provided at the most contracted position of the piston rod in order to obtain the absolute position of the stroke, and the position where the tip of the piston rod passes through this limit switch is used as the stroke reference. Reset as a point. Therefore, it is necessary to displace the limit switch every time the hydraulic cylinder is activated.

As a position detecting device for shortening this reset operation, as disclosed in Japanese Utility Model Laid-Open No. 4-71114, a main scale for detecting an increment value and a sub-scale for measuring a reference point are provided. It is known that each of them has an absolute position by passing two reference points from an arbitrary stroke position of a hydraulic cylinder.

[0005]

However, in the above-mentioned conventional apparatus, since two magnetic scales are arranged in one actuator, the number of parts of the apparatus increases and the cost increases, and the main scale and the sub-scale are also increased. There is a problem that it cannot be applied to the actuator that rotates the rod because it is necessary to maintain the positional relationship of
Further, since two reference points are passed to set the absolute position, there is a problem that the time required for activation may increase.

Therefore, an object of the present invention is to provide a position detecting device which can detect a reference point immediately by a magnetic scale having a simple structure and can be used also for an actuator which rotates a rod.

[0007]

According to the present invention, in FIG. 1, a magnetic scale 2 in which weak magnetic portions having a predetermined depth B ₀ are arranged at a predetermined pitch in a moving direction of an actuator 30, Corresponding to the pitch of the magnetic scale 2 and a reference point formed by forming a weak magnetic portion corresponding to a reference position provided at a predetermined position of the magnetic scale 2 in the weak magnetic portion at a predetermined depth corresponding to the reference position. And a pair of magnetic sensors 5 for outputting two-phase sine wave signals having a phase difference of 90 degrees, and means 1 for calculating the relative position from the outputs of these magnetic sensors 5.
0, means 20 for detecting a reference point from the output of the magnetic sensor 5, means 22 for determining an amplitude level at the reference point, and means 24 for storing an absolute position corresponding to the reference point of the magnetic scale 2. Means 25 for determining the moving direction of the actuator 30 based on the output signal of the magnetic sensor 5, and means 23 for controlling the absolute position signal of the storing means 24 based on the amplitude level of the reference point and the moving direction of the actuator. And the absolute position signal control means 23
Is provided with a means 21 for calculating an absolute position from the absolute position of the reference point read by and the calculated relative position.

[0008]

Therefore, when the actuator is activated, the reference point is detected based on the amplitude level of the sine wave output by the magnetic sensor when passing through the weak magnetic portion of the magnetic scale. The position of the reference point is determined from the magnitude of the amplitude level. The position of the reference point and the displacement direction of the actuator detected from the sine wave having a phase difference of 90 degrees from the magnetic sensor are used as parameters to calculate the address of the means for storing the absolute position, and the calculated address is stored. The present absolute position is set as the absolute position of the detected reference point, and thereafter, the absolute position of this reference point plus the relative displacement is output as the absolute position.

[0009]

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 4) which constitutes a hydraulic cylinder (not shown), and the surface of the piston rod 1 is provided with a predetermined pitch P in the axial direction. The magnetic scale 2 is formed by forming the weak magnetic portion 3 having the depth B ₀ .

The width of the weak magnetic portion 3 is P / 2 which is half of the pitch P, and both the weak magnetic portion 3 and the ferromagnetic portion 4 of the magnetic scale 2 have a width of P / 2 and alternate at the pitch P. Is installed in.

Of the weak magnetic portions 3 of the magnetic scale 2, the depths of the weak magnetic portions 3 corresponding to the _five reference points h _{1 to} h 5 preset on the magnetic scale 2 are different from the depths B ₁ to B, respectively. _Five
And the reference points h ₁ , h ₂ , h ₃ , h ₄ , h ₅ are set at equal intervals of 4 pitches. The depths of these weak magnetic portions 3 satisfy the relationship of B ₀ <B ₁ <B ₂ <B ₃ <B ₄ <B ₅ .

At one end of a hydraulic cylinder (not shown), a pair of magnets that output two-phase sine waves having a phase difference of 90 degrees with one pitch of the magnetic scale 2 as one cycle according to the displacement of the piston rod 1. A sensor 5 is provided. As shown in FIG. 4, the output signal of the magnetic sensor 5 is output as output signals sigA and sigB having a phase difference of 90 degrees.

The two-phase output signals from the magnetic sensor 5 are sig
As shown in FIG. 3, A and sigB are input to the controller 7 including a microcomputer, 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, for example, in Japanese Patent Laid-Open No.
As disclosed in Japanese Laid-Open Patent Publication No. 136713, a position (coarse position) of 1/2 P unit and 1 based on a normalization coefficient obtained based on each peak value of the output signals sigA and sigB of the magnetic sensor 5 The relative position of the stroke is obtained by obtaining a position (fine position) obtained by dividing the / 2 pitch into a predetermined number, and summing the fine position and the coarse position.

The output signals sigA and sigB of the magnetic sensor 5 are sample hold circuits SHA and SHB, as shown in FIG.
And via the analog-digital converter ADC to the central processing unit CPU of the controller 7.

The comparators CA and CB output signals sigA and sigB with the center level, which is the median between the maximum and minimum values of the output signals sigA and sigB of the magnetic sensor 5 calculated by the CPU, as a reference value. By comparison, H level is higher than the center level, and L is lower than the center level.
Output level signal. It should be noted that DACA and DACB are digital-analog converters that perform analog conversion of each center level calculated by the CPU.

The comparator CZ determines the reference points h _{1 to} h ₅ when the output signal sigA of the magnetic sensor 5 is at the center level cenA. The digital-analog converter DACZ
Reference point judgment level basZ given from and output signal sigB
And the output signal sigB is compared with the reference point determination level basZ.
A signal of H level is output when it is larger, and an L level signal is output when it is smaller.

The determination of the reference point is performed by interrupt processing when the output of the comparator CA changes, that is, when the output signal sigA passes the center level, and the reference point is determined by software described later.

The output signal of the magnetic sensor 5 is stored in the memory RAM.
The peak value for each pitch of sigA and sigB is stored, and the absolute position information at each reference point is also stored.
The memory RAM is backed up by a battery and the like, and the stored contents are retained even when the power supply of the device is cut off.

A method of determining the reference point and the stroke direction will be described with reference to FIG.

When the piston rod 1 is displaced, the output signals sigA and sigB of the magnetic sensor 5 are output as sine waves having a phase difference of 90 degrees. When the output signals sigA and sigB pass through the weak magnetic portion 3 having the depth B ₀ , they have an amplitude level V
_0, when passing through the weak magnetic portion 3 of the reference point depth B ₁ .about.B ₃ amplitude level V ₀ is larger than the amplitude level V ₁ ~V ₃
Are output respectively. Although not shown, the amplitude levels V ₄ and V ₅ are output at the reference points B ₄ and B ₅ . Therefore, the amplitude level at the reference points h _{1 to} h ₅ becomes V ₁ or more, and the amplitude level becomes V _{0 in} the other weak magnetic portions 3, and the reference point is detected from the amplitude level and the position of the reference point is easily determined. can do.

At each reference point, the output signal sigA is the center level cen
At the reference point of A, the output signal sigB shows the minimum peak value, which is less than or equal to cenB−V ₁ , but may vary due to formation errors such as the depth B ₀ of the weak magnetic portion 3. While the reference point is determined on the condition that the output signal sigB is equal to or lower than the preset reference point determination level basZ, the minimum peak value when passing through the weak magnetic portion 3 other than the reference point can be excluded.

This reference point judgment level basZ is the output signal s
It can be set according to the following expression from the center level cenB of igB and the amplitude level of the output signal sigB.

BasZ = cenB- (V ₀ + V ₁ ) / 2 Therefore, when the output signal sigA becomes the center level cenA, if the output signal sigB is below the reference point determination level basZ (hatched portion in the figure), the reference It is easily determined to be a point.

On the other hand, the stroke direction of the piston rod 1 is judged because the output signal sigB takes the maximum or minimum level at the position where the output signal sigA becomes the center level cenA.
In the interrupt processing of the comparator CA shown in FIG. 3, CA, C
It can be easily determined (exclusive OR) whether or not the output value of B is in agreement with either H or L. When they are in agreement, the piston rod 1 is in the negative direction, otherwise it is in the positive direction. Determine to move.

Next, the processing in the controller 7 from the determination of the reference point to the setting of the absolute position will be described with reference to the flowchart of FIG. Note that FIG. 5 shows a flow from turning on the power of the apparatus to setting the absolute position of the reference point.

First, after resetting the stroke position in S10, the piston rod 1 is driven in an arbitrary direction by a driving means (not shown), and an output signal sig is output in S11.
The reference point is determined by determining whether A is the center level cenA and the output signal sigB is equal to or lower than the reference point determination level basZ.

When the reference point is detected, in S12, the stroke position at that time, that is, the relative position calculated as the weak magnetic portion 3 passes, is held at X, and the amplitude level of the output signal sigB is set to V. And the positive or negative of the stroke is S
Hold each.

In step S13, the process is determined depending on whether the stroke is positive or negative.

In S14 and S15, predetermined conversion factors base1 to 2 are given according to the displacement direction of the piston rod 1, and the conversion factor base1 is obtained by multiplying the detected amplitude level V of the reference point by a predetermined conversion constant m. The value obtained by adding up to 2 is obtained as the address AD of the memory RAM for storing the absolute position of the current reference point. The conversion constant m is a constant for converting the amplitude level V of the reference point into the address of the memory RAM.

Here, as shown in the memory map of FIG. 6, the contents of the memory RAM are the stroke direction and the conversion coefficient.
base _{1 to 2} , base point h _{1 in} the order of reference point amplitude level V
The absolute position of ~ h ₅ is stored.

In this memory map, the absolute positions of the same reference point are redundantly stored at different addresses. However, the absolute positions of the overlapping reference points of the respective addresses are not necessarily equal, and this is because the absolute position of the piston rod 1 is different. The detection position of the reference point depending on the displacement direction (the output signal sigA is the center level cen
This is because the position (equal to A) is slightly deviated. Therefore, the absolute position of each of the reference points h _{1 to} h ₅ is stored in the correct absolute position by changing the address for each displacement direction of the piston rod 1.

In S16, the absolute position stored in the memory RAM is read based on the address AD obtained in S14 to 15, the read absolute position is set to the current reference point, and the relative position calculated thereafter is calculated. It becomes possible to output the absolute position by adding the positions.
Then, the absolute position setting completion signal is output from the controller 7, and the driving means of the hydraulic cylinder (not shown) can drive based on the measured absolute position of the piston rod 1.

Therefore, even if the piston rod 1 is displaced due to oil leakage or the like while the apparatus is at rest, it is possible to automatically set the absolute position by passing at least one arbitrary reference point. The stroke amount can be reduced to shorten the time until the operation, and the depth of the weak magnetic portion 3 is set to B ₀ in one magnetic scale 2, while the weak magnetic force corresponding to the reference points h _{1 to} h ₅ is set. The depth of part 3 is B ₁ ~
Since it is set to B ₅ , the absolute position can be set by detecting one reference point near the stroke position immediately after the start, and the stroke amount of the piston rod 1 can be reduced and the start time can be shortened.

Further, the relative position and the absolute position can be detected by one set of magnetic scale and magnetic sensor, and an absolute value type highly accurate position detecting device can be constructed without increasing the number of parts. Since the weak magnetic portions 3 arranged at a predetermined pitch P are arranged all around the piston rod 1, the rotation of the piston rod 1 can be permitted.

On the other hand, in order to reset the absolute positions of the reference points h _{1 to} h ₅ at the predetermined addresses in the memory RAM, as shown in the flowchart of FIG.
Is moved to the most contracted position, the relative position at this time is set to zero, and then the operations of S21 to S26 are repeated to expand or contract the piston rod 1 to calculate the relative position calculated when passing each reference point. The absolute position can be automatically set while setting the position in the memory RAM. Note that S21 to S25 are the same as S11 to S15 in the flowchart of FIG.

Since the relative position is set to zero at the most contracted position of the piston rod 1, the detected relative position of the reference point is equivalent to the absolute position, and the above processing is performed in the extension direction and the contraction direction of the piston rod 1, respectively. Thus, the absolute position of each reference point can be set easily and accurately.

[0039] Figure 8 illustrates another embodiment, the contrast of the reference point h ₁ to h ₅ is disposed at equal intervals in the first embodiment, seven criteria of h ₁ to h ₇ the scale 2 In addition to setting the points, the reference points h ₁ and h ₂ and h ₆ and h ₇ are formed at 6 pitches respectively, and the reference points h _{2 to} h ₆ are arranged at equal intervals of 1 pitch. The depths B ₁ to B ₇ of the points h _{1 to} h ₇ are set to different depths, respectively, and the other configurations are the same as those in the first embodiment.

As described above, even if the reference points are arranged at unequal intervals, the absolute position can be set in the same manner as in the first embodiment, and the absolute positions can be set at arbitrary positions regardless of the intervals. It becomes possible to provide a reference point.

If the reference point h ₁ is the contraction side stroke end alarm position and the reference point h ₇ is the extension side stroke end alarm position, an alarm is issued when the piston rod 1 is about to collide with each stroke end. As a result, the piston rod 1 can be prevented from completely contracting or extending.

FIG. 9 shows still another embodiment, in which the first
Alternatively, the calculation of the relative position in the second embodiment is disclosed in Japanese Patent Laid-Open No.
It is configured by the position detecting device disclosed in Japanese Patent No. 136713, and other configurations are similar to those of the first embodiment.

Since the value obtained by adding the coarse position in 1/2 pitch units and the fine position obtained by dividing the 1/2 pitch into a predetermined number is output as the relative position, the resolution of the stroke position can be improved.

Although the weak magnetic portion 3 is formed on a part of the surface of the piston rod 1 in the above embodiment, the piston is formed by forming the weak magnetic portion 3 on the entire circumference, although not shown. It becomes possible to allow the rotation of the rod 1.

Further, in the above embodiment, the current stroke position is replaced with the absolute position stored in the memory RAM when the reference point is detected, but this replacement may be performed a plurality of times. After replacing the current position with the absolute position stored in the memory RAM at the time of input, the absolute position of the stroke calculated at each reference point and the memory RAM
The absolute position stored in the memory RAM may be read out and replaced when the absolute position of the calculated stroke amount is different by comparing with the stored value of.

Further, in the above-mentioned embodiment, the depths B _{1 to} B ₅ of the reference points are set to be successively increased, but the reference points need only be set so as not to have the same depth as other reference points. , For example, although not shown, B ₁ > B ₂ > B ₃ > B ₄ >
It may be set as B _5.

[0047]

As described above, according to the present invention, even if the actuator is displaced while it is at rest, it is possible to automatically set the absolute position by passing one arbitrary reference point. The stroke amount of can be greatly reduced to shorten the time until operation, and while a weak magnetic part that measures the relative position is provided on one magnetic scale, one of these weak magnetic parts that corresponds to the reference point Since they are formed at different depths, it is possible to configure an absolute value type position detection device by suppressing an increase in the number of parts by one set of magnetic scale and magnetic sensor, and to form weak magnetic parts arranged at a predetermined interval. By arranging the actuator around the entire circumference of the rod or the like, the absolute position can be measured while allowing the rotation of the rod.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a schematic 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 changes in the output signal of the magnetic sensor at each pitch.

FIG. 5 is a flowchart showing an example of an absolute position setting operation.

FIG. 6 is a diagram showing the contents of a memory.

FIG. 7 is a flowchart showing an operation of setting an absolute position corresponding to a reference point.

FIG. 8 is an explanatory diagram of a magnetic scale showing another embodiment.

FIG. 9 is a block diagram of relative position calculating means showing still another embodiment.

[Explanation of symbols]

 1 Piston Rod 2 Magnetic Scale 3 Weak Magnetic Part 4 Ferromagnetic Part 5 Magnetic Sensor 7 Controller 10 Relative Position Calculating Means 20 Reference Point Detecting Means 21 Position Signal Calculating Means 22 Amplitude Level Determining Means 23 Absolute Position Signal Controlling Means 24 Absolute Position Storing Means 25 Stroke Direction Discriminating Means 30 Actuator

Claims (1)

[Claims] 1. A magnetic scale having weak magnetic portions formed with a predetermined depth arranged at a predetermined pitch in a moving direction of an actuator, and a magnetic scale arranged at a predetermined position of the magnetic scale among the weak magnetic portions. A weak magnetic portion corresponding to the reference position is formed with a predetermined depth corresponding to the reference position, and a two-phase sine wave having a phase difference of 90 degrees corresponding to the pitch of the magnetic scale is output. A pair of magnetic sensors, a means for calculating a relative position from the outputs of these magnetic sensors, a means for detecting a reference point from the output of the magnetic sensor, a means for determining an amplitude level at the reference point, and a magnetic scale of the magnetic scale. Means for storing the absolute position corresponding to the reference point, means for determining the moving direction of the actuator based on the output signal of the magnetic sensor, amplitude level of the reference point and moving direction of the actuator A means for controlling the absolute position signal of the storage means based on the above, and a means for calculating the absolute position from the absolute position of the reference point read by the absolute position signal control means and the calculated relative position. Characteristic position detection device.