JP3220278B2 - 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 a piston rod and the like.

[0002]

2. Description of the Related Art In order to detect the stroke position of a piston rod of a hydraulic cylinder, a magnetic scale is prepared by embedding a weak magnetic material at a constant pitch interval in the axial direction on the surface of the piston rod. Several devices have been proposed which perform position detection with high resolution by utilizing the fact that the output signal changes as a sine wave due to the movement of the piston rod (Japanese Patent Laid-Open No. 4-136713).
Reference).

[0003] Referring to Fig. 3 , the stroke detecting unit is composed of a magnetic scale 3 having weak magnetic parts 2 formed at equal intervals on the surface of a piston rod 1 made of a ferromagnetic material in the stroke direction (left-right direction in the figure). And a magnetic sensor 4 attached to the cylinder side of the hydraulic cylinder. When the piston rod 1 moves, for example, in the extending direction (leftward), the magnetic sensor 4 outputs a two-phase two-phase signal for one pitch of the magnetic scale. Sinusoidal voltages v _A , v _B are output, and one set of elements 4A, 4B is compared with the other set of elements 4A, 4B.
Since C and 4D are shifted in the right direction by 1/4 pitch in the drawing , a 90-degree phase difference is generated between the two-phase sine wave voltages v _A and v _B as shown in FIG .

[0004] The two-phase sine wave output waveform by the comparator molded to pulse V _A, is converted to V _B, using these, and the like enter the two pulses (also referred to as a direction discrimination) phase discrimination by-multiplier circuit pulse V _a, a pulse train rises respectively rising and falling of V _B is made as shown in FIG. 4. By counting this pulse train with an up / down counter, a stroke position obtained by dividing one pitch into quarters can be detected. In practical use, one pitch is 2 mm, and therefore, detection can be performed up to a unit of 0.5 mm.

[0005]

In order to increase the resolution (detection accuracy), the stroke position (position obtained by dividing one pitch into quarters) obtained as described above is used as a coarse position in the above apparatus. In addition, the two-phase sine wave output is input to a controller mainly consisting of a microcomputer, and waveform processing is performed inside the controller to calculate a fine position in units of 0.01 mm, and the stroke is calculated by adding the coarse position to the fine position. The position is required with high accuracy.

However, in this case, since a microcomputer is required for waveform processing, a controller is expensive.

Accordingly, an object of the present invention is to perform position detection with high accuracy with an inexpensive configuration without using a microcomputer.

[0008]

SUMMARY OF THE INVENTION claims 1 invention, (a) a magnetic scale which is formed by arranging a weakly magnetic material with a predetermined pitch in the direction of movement, (b) two sets of magneto-resistive elements and these A magnetic sensor that outputs a sine wave having one cycle of one pitch of the magnetic scale with a phase difference of 90 degrees, and (c) when the sensor output of each phase is a positive value (D) an absolute value circuit for calculating the absolute value of each phase sensor output, and (e) a subtractor for calculating the difference between the two absolute value circuit outputs. (F) an amplifier that outputs a pulse that goes high only when the subtraction result of the subtractor is a positive value; and (g) a pulse from all the amplifiers is input and the rising and falling of each pulse is input. Working together at the edge And (h) means for calculating a position using a pulse train from the pulse generation circuit.

[0009]

The two-phase sensor output having a phase difference of 90 degrees is
When converted into a pulse by the two amplifiers in (c), the rising and falling edges of the pulse become 1 as in the conventional case.
There will be a total of four per pitch.

[0010] sensor output of two more phases in the invention of claim 1, two absolute value circuits (d), the subtractor (e),
When converted to a pulse by the amplifier of (f), this pulse has a total of four rising and falling edges per pitch, and these edges are (c)
Since the pulse is generated at a position different from the edge of the pulse converted by the two amplifiers, eight pulse trains are generated per pitch from the pulse generation circuit of (g).

From this, a position obtained by dividing one pitch into eight is detected, and the accuracy is doubled as compared with the conventional example in which one pitch is divided into four.

No microcomputer is used in the signal processing circuit.

[0013]

Stroke detecting unit of EXAMPLES of the hydraulic cylinder piston rod is the same as conventional as also shown in FIG.

In FIG . 3 , grooves are formed at predetermined intervals in the axial direction on the surface of a piston rod 1 formed of a magnetic material, and weak magnetic members 2 are formed in the grooves to form a weak magnetic portion 2 at an equal pitch. Thus, the magnetic scale 3 is formed. The width of the weak magnetic portion 2 is exactly half of one pitch P.

A magnetic sensor 4 comprising two sets of magnetoresistive elements and a bias magnet is provided on the cylinder side (for example, near the bearing) of the hydraulic cylinder.
2 outputs a two-phase sine wave with one pitch of the magnetic scale 3 as one cycle and a phase difference of 90 degrees with the displacement of the piston rod 1 as shown in FIG.

More specifically, each of the magnetoresistive elements 4A, 4B, 4
When a magnetic field is applied to a substance in which current is flowing,
An element utilizing the phenomenon that the resistance increases (so-called magnetoresistance effect), and a set of magnetoresistance elements 4 connected in series
When the piston rods 1 are moved near the surface of the piston rod 1, the magnetoresistive elements 4A, 4B
The magnetic flux density from the bias magnet 4G passing through
As a result, the resistance values R _A1 and R _A2 of each element change. When the output between the two elements 4A and 4B is taken out in order to capture this change in the resistance value, the output voltage v _A is represented by a sinusoidal waveform having one pitch of the magnetic scale 3 as one cycle with the displacement of the piston rod 1. Change.

Another set of magnetoresistive elements 4C and 4D having the same characteristics as the set of magnetoresistive elements 4A and 4B are shifted from the set of elements 4A and 4B by 1/4 pitch to the right in the figure. When arranged, the output voltage v _B between another pair of elements 4C, 4D is delayed by 90 degrees with respect to the output waveform of v _A when the piston rod moves (extends) to the left in the figure. It has a sine waveform. If v _A = H · sin θ (where H is the amplitude), then v _B = H · sin (θ−90 °).

The two elements 4A, 4B, 4 shown in FIG.
The width dimensions in the left and right directions of C and 4D indicate roughly, and are not actual dimensions. The power supply voltage Vc is applied to the two sets of elements.
By applying c, a current flows through each element.

FIG. 1 is a block diagram of a circuit for processing the two-phase sine wave outputs v _A and v _B from the magnetic sensor 4.

Reference numerals 13 and 14 denote absolute value circuits, each of which outputs v _A ,
v computes the absolute value of _B. This absolute value circuit may be composed of, for example, a full-wave rectifier circuit. By this absolute value circuit, the negative half-cycle waveforms of the outputs v _A and v _B are inverted to the positive side as shown in FIG. Is done.

[0021] These absolute value | v _A |, | in the subtracter 15 is input, the absolute value | | v _B v _A | from | v _B | is subtracted.

The result of this subtraction also becomes a sine wave as shown in FIG. 2, and when one cycle (360 ° section) of the sine wave output v _A corresponding to one pitch is observed, the origin and 45 °, 135 °
Intersects at four points: 225 degrees and 315 degrees.

The amplifier 16 to which the result of the subtraction is input is composed of a comparator that outputs a signal that goes high only when the input signal is positive, together with the other two amplifiers 11 and 12. At 12, a pulse signal is generated as shown in FIG.

An edge trigger pulse circuit 17 to which pulse signals from all the amplifiers 16, 11, and 12 are input is constituted by a flip-flop. The pulse circuit 17 operates at all rising and falling edges of the pulse. Generate a pulse.

The outputs of the amplifiers 16, 11, 12 each have four, two, and two edges per pitch (amplifier 16).
, Two rising edges and two falling edges, and the outputs of the amplifiers 11 and 12 have one rising edge and one falling edge), and the positions of the edges do not overlap, so that a total of 8 (= 4 + 2 + 2) A pulse train is generated. Moreover, the angle at which the pulse is generated is 0.
Degrees, 45 degrees, 90 degrees, 135 degrees, ..., 315 degrees, and 45
It is equally spaced every degree.

In this way, when eight pulse trains are generated per pitch of the magnetic scale 3, the pulse trains are counted by an up-down counter or the like (for example, counting up in the extension direction of the piston rod, counting down in the contraction direction). ), It is possible to detect a stroke position obtained by dividing one pitch into eight. In the past, one pitch was only divided into four, so that the accuracy was improved twice as much as in the conventional case. For example, if the pitch is 2 mm, the resolution is 0.25 m.
m.

Further, as shown in FIG. 1, a simple circuit including two absolute value circuits 13 and 14, one subtracter 15, and one amplifier 16 is added, and the circuit is constructed without using a microcomputer. Therefore, the cost does not increase so much.

Since the two sets of magnetoresistive elements have the same performance, even if the sensor output changes due to aging or abrasion of the sliding portion, a small change occurs in the pulse interval.

In FIG. 1, a subtractor 15 and an amplifier 16 are connected.
It is also possible to configure a single differential amplifier.

[0030]

In the claims 1 invention, according to the present invention, a magnetic scale which is formed by arranging a weakly magnetic material with a predetermined pitch in the direction of movement,
A magnetic sensor comprising two sets of magneto-resistive elements and a voltage source for passing a current through them, outputting a sine wave having one pitch of the magnetic scale as one cycle with a phase difference of 90 degrees, and a sensor output of each phase. An amplifier that outputs a pulse that goes high only when the value is a positive value, an absolute value circuit that calculates the absolute value of the sensor output of each phase, and a subtractor that calculates the difference between the two absolute value circuit outputs. An amplifier that outputs a pulse that goes high only when the subtraction result of the subtracter is a positive value, and a pulse that receives pulses from all of the amplifiers and operates together at the rising and falling edges of each pulse. And a means for calculating the position using the pulse train from this pulse generation circuit, so that the position can be detected with twice the accuracy without using a microcomputer. It can be.

[Brief description of the drawings]

FIG. 1 is a block diagram of a signal processing circuit according to one embodiment.

FIG. 2 is a waveform diagram at each position of a signal processing circuit.

FIG. 3 is a detailed view of a conventional stroke detection unit.

FIG. 4 is a waveform diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston rod 2 Weak magnetic part 3 Magnetic scale 4 Magnetic sensor 4A-4D Magnetic resistance element 4G Bias magnet 11,12 Amplifier 13,14 Absolute value circuit 15 Subtractor 16 Amplifier 17 Edge trigger pulse circuit

Claims (1)

(57) [Claims] 1. A magnetic scale formed by arranging weak magnetic materials at a predetermined pitch in a moving direction, two sets of magnetoresistive elements, and a voltage source for supplying a current to these magnetic scales. A magnetic sensor that outputs a sine wave having one cycle with a phase difference of 90 degrees, an amplifier that outputs a pulse that goes high only when the sensor output of each phase is a positive value, and an absolute value of the sensor output of each phase. An absolute value circuit for calculating each value, a subtractor for calculating the difference between the outputs of the two absolute value circuits, an amplifier for outputting a pulse which becomes high only when the subtraction result of the subtractor is a positive value, A circuit that receives pulses from all the amplifiers and operates together at the rising and falling edges of each pulse to generate a pulse; and calculates the position using a pulse train from the pulse generation circuit. Position detecting device characterized by providing a means that.