JP3136012B2 - Position detection device - Google Patents

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 a stroke position of an actuator such as a piston rod of a hydraulic cylinder with high accuracy.

[0002]

2. Description of the Related Art As a device for detecting a stroke position of a piston rod or the like of a hydraulic cylinder, a magnetic scale having a weak magnetic portion formed at a constant interval in the axial direction on the surface of the piston rod is formed, and a magnetic scale attached to the cylinder side. A relative position detection type is known in which the detection signal of the sensor changes in a sine waveform with the displacement of the piston rod, and a position with high resolution is detected from an increment value of the displacement.
The applicant of the present application has also proposed in Japanese Patent Application Laid-Open No. 4-136713 a device capable of performing 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 at which the tip of the piston rod has passed this limit switch is used as a reference for the stroke. Reset as a point. For this reason, every time the hydraulic cylinder is activated, it is necessary to displace the hydraulic cylinder to the most contracted position.

As a position detecting device for shortening the reset operation, a main scale for detecting an increment value and a sub-scale for measuring a reference point are disclosed in Japanese Utility Model Laid-Open No. 4-71114. It is known that each of them is provided with 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, at the start of use, it is necessary to detect at least two reference points by moving the actuator to detect the reference points. In some cases, since the stroke position cannot be determined, the stroke may always be made to the safe side, and since the stroke is not always made to the adjacent reference point side, the reset time may be increased.

Accordingly, an object of the present invention is to provide a position detecting device capable of easily determining the stroke direction of an actuator and setting an absolute position in a short time.

[0007]

According to the present invention, in FIG. 1, weak magnetic portions formed at predetermined different depths at predetermined positions are arranged at predetermined pitches in the moving direction of the actuator. A main scale 2 as a first magnetic scale, and a pair of first scales that output a sine wave having a phase difference of 90 degrees corresponding to the pitch of the main scale 2
, A means 10 for calculating a relative position from the output of the first magnetic sensor 5, a means 20 for determining the amplitude level from the output of the first magnetic sensor 5, and a position which does not overlap with the main scale 2. disposed in a weak magnetic portion formed at a predetermined depth, the plant in the direction of movement of the actuator
A sub-scale 6 as a second magnetic scale disposed at a predetermined pitch corresponding to a reference point at a fixed position ,
A pair of second magnetic sensors 9 that output a sine wave having a phase difference of 90 degrees corresponding to the pitch of the sub-scale 6
A means 21 for detecting a reference point from the output of the second magnetic sensor 9, a means 22 for calculating an interval between the reference point and a reference point detected immediately before, and a function corresponding to the reference point of the sub-scale 6. Means 24 for storing the absolute position in advance, means 23 for controlling the absolute position signal of the storage means 24 based on the determination result of the amplitude level and the interval between the reference points, and a reference point read by the absolute position signal control means 23. Means 2 for calculating an absolute position from the absolute position of the object and the calculated relative position
5 is provided.

[0008]

Therefore, when the actuator is started, the relative position is calculated from the sine wave output from the first magnetic sensor when passing through the weak magnetic portion of the main scale.
When the reference point is detected from the amplitude level of the sine wave output by the second magnetic sensor when passing through the weak magnetic portion of the sub-scale,
The position of the reference point is determined by comparing the amplitude levels of the first magnetic sensor. Further, an interval between the reference point detected immediately before and the current reference point is calculated from the calculated relative position. The amplitude level of the output of the first magnetic sensor at the reference point,
The address of the means for storing the absolute position is calculated using the distance between the reference points and the displacement direction of the actuator based on the sign of the distance between the reference points as parameters, and the absolute position stored at the calculated address is calculated as the absolute value of the current reference point. The position is set as a position, and the sum of the absolute position of the reference point and the relative displacement is output as the absolute position.

[0009]

1 to 3 show an embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes a piston rod formed of a magnetic material (ferromagnetic portion 4) which constitutes a hydraulic cylinder (not shown). The weak magnetic portions 3 formed at a depth M ₁ up to the center position of 1/2 of the stroke and at a depth M ₂ from the center position of this stroke to the most extended position are arranged at a predetermined pitch P. The main scale 2 is constituted by the weak magnetic part 3 and the ferromagnetic part 4. The widths of the weak magnetic portions 3 and the ferromagnetic portions 4 alternately arranged in the axial direction are each 配 P.

A sub-scale 6 is formed on the outer periphery of the piston rod 1 which does not overlap with the main scale 2 in the axial direction. Subscale 6 is formed by a reference point h1~h12 corresponding to the main scale 2 composed of weak magnetic portion 7 of a predetermined width and a reference point at an interval L ₀ around the center position of 1/2 of the total stroke h6,7 arranged to further from the reference point h7 toward the outermost extended position while arranging the reference point h8~12 at intervals L ₁ ~L ₅ with increased (rightward in the drawing) sequentially distance, the reference from point h6 toward the lowest retracted position reference point interval L ₁ ~L ₅ with increased (left direction in the drawing) sequentially distance h5~
h1 is provided, and reference points h1 to h6 and reference points h7 to h12 are provided.
Are arranged symmetrically with respect to the center position. Here, in each of the axial width of the reference point H1 to H12 L _0/2, is formed by the weak magnetic portion 7 of a predetermined depth S, the distance L ₀ ~L ₅ is L
₀ <L ₁ <L ₂ <L ₃ <L ₄ <L ₅
The difference L _{n + 1} -L _n of adjacent intervals is set to a resolution greater than the main scale 2.

At one end of a hydraulic cylinder (not shown), a pair of magnetic fields which output a two-phase sine wave having a phase difference of 90 degrees with one pitch of the main scale 2 as one cycle in accordance with the displacement of the piston rod 1. A sensor 5 is provided as a first magnetic sensor. Similarly, at one end of the hydraulic cylinder 1, one cycle of the sub-scale 6 is set to one cycle in accordance with the displacement of the piston rod 1, and two phases having a phase difference of 90 degrees are provided. Is provided as a second magnetic sensor.

The output of the magnetic sensor 5 accompanying the displacement of the piston rod 1 is output as two-phase output signals sigA and sigB having a phase difference of 90 degrees as shown in FIG. As shown in FIG. 5, the signals are output as two-phase output signals Z _A and Z _B having a phase difference of 90 degrees.

A two-phase output signal sig from the magnetic sensor 5
A and sigB are relative position calculating means 1 as shown in FIG.
The relative position signal is calculated based on the two-phase signals having a phase difference of 90 degrees and input to 0, and the relative position signal is sent to the position signal calculating means 25. On the other hand, the output signals sigA, sigB From the amplitude level of the main scale 2
The stroke position with respect to the center position is determined.

_A two-phase output signal Z _A from the magnetic sensor 9,
Z _B is input to the reference point detection means 21 to detect a reference point position as described later based on the peak value of the amplitude level,
The reference point interval calculation means 22 calculates a reference point interval from the detected reference point position and the reference point position detected immediately before. The absolute position control means 23 reads the absolute position of the reference point preset in the absolute position storage means 24 constituted by a storage means such as a memory from the calculated reference point interval and the determination result of the amplitude level, and calculates the position signal. The means 25 calculates the absolute position of the stroke by adding the calculated relative position signal and the read absolute position of the reference point.

The relative position calculating means 10 is constructed as shown in FIG. 3, and updates and stores the peak value of each of the output signals sigA and sigB of the magnetic sensor 5 by the peak value updating / storing means 11 for each pitch. The loudness value calculating means 12 calculates the sensor output sig from these peak values as shown in FIG.
The center values cenA and cenB, which are the center values of the amplitudes of A and sigB, are calculated. The normalization coefficient calculation means 13 calculates the reciprocal of the difference between the detected peak value and the center value as a normalization coefficient, and the sensor output correction means 14 converts the two-phase output signals sigA and sigB of the magnetic sensor 5 into normalization coefficients. Are multiplied to equalize each amplitude level to correct the output signal.

Fine position calculating means 15 and coarse position calculating means 1
6 is based on the corrected two-phase sensor output.
It is obtained by a trigonometric function inverse operation disclosed in Japanese Patent No. 713. That is, while obtaining the coarse position in 1 / 2P units,
The fine position calculating means 15 obtains a fine position obtained by dividing 1 / 2P into a predetermined number from the center values cenA and cenB and the peak value, and the relative position calculating means 17 adds the calculated fine position and coarse position. Is used to determine the relative position of the stroke.

On the other hand, the detection of the reference point is performed based on the output signal of the magnetic sensor 9 of the sub-scale 6. A method of determining the reference point will be described with reference to FIG.

When the piston rod 1 is displaced, the two-phase output signals Z _A and Z _B of the magnetic sensor 9 are output as sine waves having a phase difference of 90 degrees as shown in FIG. each reference point as a position to become the output signal Z _a is FuHisashichi cenz _a (in the figure mark ●). The output signal Z at this time
_B is substantially the minimum peak value, to eliminate such error in the depth S of the weak magnetic portion 7, the following reference judgment level basZ the output signal Z _B is set in advance (in the figure the shaded portion) and the output signal Z _A There is detected as a reference point the stroke position where the FuHisashichi cenz _a. The detection of the epicenter value and the peak value is shown in FIG.
As described above, this can be performed by a configuration similar to that of the relative position calculation means 17 .

Here, the position of the detected reference point is determined based on the interval from the immediately preceding reference point, as described later. As shown in FIG. Since the reference point is disposed at a target position with the center position of the piston rod 1 as an axis, it is determined whether the detected reference point is on the most contracted position side or the most extended position side with respect to the center position.

That is, as shown in the flowchart of FIG. 6, the two-phase output signals sigA and sigB of the magnetic sensor 5 are simultaneously read at the position where the reference point is detected in S1, and
In 2, the amplitude amp of these output signals is calculated by the following equation.

[0022]

(Equation 1)

As shown in FIG. 4, the output signals sigA and sigB output a level 1 amplitude in the weak magnetic portion 3 having a depth M _{1 and} a level 2 amplitude in the weak magnetic portion 3 having a depth M _2. ,
It is determined which side of the center position of the stroke is the reference point detected based on the amplitude level of the output signal.

In step S3, the calculated amplitude "amp" is compared with the intermediate value between the known values "level 1" and "level 2" as a threshold value. If "amp" is larger than the threshold value, the amplitude level is set to "2" in step S4. On the other hand, if it is smaller, the amplitude level is set to 1 in S5. If the amplitude level is 1, the detected reference point is on the left side of the center position in FIG. 2, and if the amplitude level is 2, it is on the right side of the center position.

Next, the processing after determination of the reference point will be described with reference to FIG.
This will be described with reference to the flowchart of FIG. FIG.
Shows the flow from when the power of the apparatus is turned on until the absolute position of the reference point is set.

First, in S10, the main scale 2
After resetting the position data, the piston rod 1 is extended by a drive means (not shown), the output signal Z _A of the magnetic sensor 9, S11, FuHisashichi cenz _A and the output signal Z _B
Is determined to be less than or equal to basZ to determine the first reference point.

[0027] When the first reference point is detected, the stroke position at that time in S12, i.e., the output signal sigA magnetic sensor 5, the relative position calculated on the basis of the sigB in X _1, the output signal sigB each holding the amplitude level a _1. Further, by driving the piston rod 1, S13
Then, the second reference point is determined in the same manner as in S11.

When the second reference point is detected in S13, S
At 14, the relative position at that time is set to X in the same manner as at S12.
_2, holds the amplitude level of the output signal sigB to A _2, S1
In step 5, the distance L between the first and second reference points held is calculated.

[0029] S16 in by comparing the minimum distance L ₀ of the absolute value and the subscales 6 intervals L mentioned above calculation, while the distance L is the processing proceeds to S18 is larger than the minimum distance L _0,
If it is smaller, the second reference point is detected again via the processing of S17.

When the interval L is smaller than the minimum interval L ₀ ,
Since the magnetic sensor 9 has passed the first reference point twice due to the expansion and contraction of the piston rod 1 and the absolute position cannot be set accurately, the relative position and amplitude level of the latest reference point are determined in S17 by the first reference point. X ₁ as point data,
With each transfer to A _1, the process returns to S13.

On the other hand, the interval L is determined to be the minimum interval L
Larger than _0, it determines whether the amplitude level A ₂ is a level 1 in the second reference point in S18. That is, the detected second reference point is h1 to h6 or h7 to h7.
It is determined whether the group belongs to any one of groups 12.

If the determination in S18 is YES, that is, it is determined that the second reference point is one of the reference points h1 to h6, and the process proceeds to S20, while if NO, the second reference point is set. h7 to h12 and S
Proceed to step 19.

In steps S19 and S20, the direction of the stroke is determined from the amplitude level and the sign of the interval L between the reference points. If the interval L is positive, the process proceeds to steps S21 and S23.
Go to Step 4.

At steps S21 to S24, a predetermined conversion coefficient base1 is calculated from the classified reference point group, the displacement direction of the piston rod 1, and the amplitude level at the current reference point.
To 4 and a conversion coefficient base1 to a value obtained by multiplying an interval L between a current reference point (the second reference point) and a previous reference point (the first reference point) by a predetermined conversion constant m. The value obtained by adding 4 is obtained as the address AD of the memory for storing the current absolute position of the reference point. Note that the conversion constant m
Is a constant for converting the interval L between the reference points into a memory address.

[0035] Here, the memory contents, the amplitude level of the output signal of the magnetic sensor 5 as shown in the memory map in FIG. 8, the stroke direction, transform coefficients Base1～4, spacing of the reference point (L ₀ ~L ₅ ), The absolute positions of the reference points h1 to h12 are stored. In this memory map, the absolute position of the same reference point is stored at different addresses in an overlapping manner. However, the absolute positions of the overlapping reference points at the respective addresses are not always equal. This depends on the displacement direction of the piston rod 1. This is because the detection position of the reference point (the position where the output signal sigA becomes equal to the center value cenA) is slightly shifted. Therefore, the absolute position of each of the reference points h1 to h12 is changed for each displacement direction of the piston rod 1 to store an accurate absolute position.

In S25, the stored absolute position is read based on the address AD obtained in S21 to S24, the absolute position read from the memory at the current reference point is set, and the relative position calculated thereafter is set. Can be added to output the absolute position.
The control means of the hydraulic cylinder not shown is a piston rod 1
Desired driving can be performed based on the absolute position of

Therefore, even if the piston rod 1 is displaced due to oil leakage or the like while the apparatus is at rest, the absolute position can be automatically set if the piston rod 1 passes at least two arbitrary reference points. The weak magnetic part 3 of
On the other hand, the sub-scales 6 are formed at different depths at predetermined intervals, while the reference points arranged at predetermined intervals are set at predetermined depths on the sub-scale 6, and the intervals between adjacent reference points are arranged at different distances. Because of this, it is possible to immediately determine which side the current stroke position is with respect to the predetermined position from the output of the magnetic sensor 5 of the main scale 2,
The direction of the reference point that can be detected with a small stroke amount is determined to shorten the setting time of the absolute position, and furthermore, by passing at least one weak magnetic portion 3 of the main scale 2, a desired position is determined for a predetermined position. Driving in a direction, for example, on the safe side of the piston rod 1, makes it possible to achieve both high reliability and high speed of the device actuator.

On the other hand, in order to reset the absolute positions of the reference points h1 to h12 to predetermined addresses in the memory, the piston rod 1 is displaced to the most contracted position shown in FIG. After setting the relative position of to zero,
By setting the relative position calculated from the output signal of the magnetic sensor 5 to a predetermined address AD of the absolute position storage means each time the reference point is determined from the output signal from the magnetic sensor 9, the absolute position is automatically set. Can be set.

Since the relative position is set to zero at the most contracted position of the piston rod 1, the relative position of the detected reference point is equivalent to the absolute position. By performing the above processing, the absolute position of each reference point can be easily and accurately determined. Can be set.

FIG. 9 shows another embodiment, in which the reference points arranged on the sub-scale 6 in the first embodiment are denoted by h1 to h.
And 11 locations of 11, disposed a reference point h6 on the central position of the stroke of the cylinder rod 1, further minimum reference point interval L ₀ are those having two, other configurations are the first embodiment Same as the example.

The identification of these equally spaced intervals L ₀ in disposed reference point h5, h7 is weak magnetic portion 3 of the main scale 2
Can be easily identified from the amplitude level based on the difference between the depths M ₁ and M ₂ in accordance with the flowcharts of FIGS.

In the above embodiment, the current stroke position is replaced with the absolute position stored in the memory when any two reference points are detected. However, this replacement may be performed a plurality of times. For example, after replacing the current position with the absolute position stored in the memory when the power is turned on again, the interval between the reference points is always calculated, and the absolute position of the stroke calculated at each reference point is compared with the stored value in the memory. Then, the absolute position stored in the memory may be read and replaced if the calculated absolute position of the stroke amount is different.

Further, in the above embodiment, the depth of the weak magnetic portion 3 of the main scale 2 is set to M ₁ and M ₂ , and the boundary is set as the center position of the entire stroke amount. It is not limited and may be from the right or from the left, and may be further classified into a greater number of depths.

In the above embodiment, the intervals L between the reference points are arranged so as to be sequentially increased or decreased. However, although not shown, the intervals L are randomly determined as L ₀ , L ₅ , L ₃ , L _1, etc. It may be provided.

[0045]

As described above, according to the present invention, even if the actuator is displaced during rest, it is possible to automatically set the absolute position if the actuator passes two arbitrary reference points. From the output of the magnetic sensor, it is possible to immediately determine which side the current stroke position is with respect to the predetermined position, and determine the direction of the reference point approaching with a small stroke amount at startup. it is possible to shorten the setting time of the absolute position and becomes the predetermined desired direction and in accordance with the stroke position against the position, for example, if brought into the drive to the actuator safe side of, the reliability and speed of the actuator Can be improved.

[Brief description of the drawings]

FIG. 1 is a block 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 showing a relative position calculating means of FIG. 1;

FIG. 4 is a diagram showing output signals of a main scale magnetic sensor at each pitch.

FIG. 5 is a diagram showing output signals of a sub-scale magnetic sensor at each reference point.

FIG. 6 is a flowchart illustrating a process of determining an amplitude level.

FIG. 7 is a flowchart illustrating an example of absolute position control.

FIG. 8 is a diagram showing the contents of an absolute position storage means.

FIG. 9 is an explanatory diagram of a magnetic scale showing another embodiment.

[Explanation of symbols]

 2 Main scale 3 Weak magnetic part 4 Ferromagnetic part 5 Magnetic sensor 6 Sub scale 7 Weak magnetic part 9 Magnetic sensor 10 Relative position calculating means 20 Amplitude level determining means 21 Reference point detecting means 22 Reference point interval calculating means 23 Absolute position signal control Means 24 Absolute position storage means 25 Position signal calculation means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-136713 (JP, A) JP-A-4-711114 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 7/00-7/34 102 G01D 5/00-5/252 G01D 5/39-5/62

Claims (1)

(57) [Claims] A first magnetic scale in which weak magnetic portions formed at predetermined different depths at predetermined boundaries are arranged at a predetermined pitch in the moving direction of the actuator;
A pair of first magnetic sensors that output a sine wave having a phase difference of 90 degrees corresponding to the pitch of the first magnetic scale, and a unit that calculates a relative position from an output of the first magnetic sensor; Means for determining the amplitude level from the output of the first magnetic sensor, and a position which does not overlap with the first magnetic scale.
A second magnetic scale in which the weak magnetic portions provided and formed at a predetermined depth are provided at a predetermined pitch corresponding to a reference point with the predetermined position as a boundary in the movement direction of the actuator; A pair of second magnetic sensors that output a sine wave having a phase difference of 90 degrees corresponding to the pitch of the second magnetic scale, and a unit that detects a reference point from the output of the second magnetic sensor; Means for calculating the interval between the reference point and the reference point detected immediately before; means for storing in advance an absolute position corresponding to the reference point of the second magnetic scale; Means for controlling the absolute position signal of the storage means from the interval, and 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 .