JPH0217281Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a fluid pressure cylinder used in a servo cylinder, etc., and in particular, the stroke of a piston rod moving in and out of the cylinder can be measured using a plurality of eddy current sensors installed on the cylinder side. The present invention relates to a fluid pressure cylinder that enables highly accurate calculation and measurement by detecting numbers.

Conventionally, as an automatic control means in a fluid pressure system, the amount of movement in and out of a piston rod in a cylinder is detected in response to a control command, and the position of movement in and out of the piston rod is determined based on the error data between the detected data and the control command data. Fluid pressure cylinders are now widely available which are designed to hold the motor at a set command position.

In addition, as a means for detecting the amount of movement in and out of the piston rod used in this case, that is, as a sensor for the movement in and out position of the piston rod, conventionally, (a) ultrasonic waves are transmitted from an ultrasonic transmitter installed on the cylinder side toward one side of the piston. A receiver installed in the cylinder receives the ultrasonic waves reflected from the side of the piston and returns, and detects the time length of the ultrasonic waves to detect the piston position, that is, the stroke of the piston rod. Things to do (Jitsukai 1976-
(No. 104606), (b) A rod serving as a light shielding member in the piston rod is moved between a large number of light emitting elements and light receiving elements arranged in parallel, and the stroke of the piston rod is electrically controlled depending on the presence or absence of output from each light receiving element. (Japanese Patent Publication No. 51-23241), (c) A device that detects the stroke of a piston rod by detecting the amount of change in capacitance corresponding to the amount of entry of the piston rod (Japanese Patent Publication No. 56-13328), (Ni) ) The movement of the piston rod is mechanically and directly detected by a detection member connected to the piston rod and provided outside the cylinder (Utility Model No. 56-104608
No.), (e) A method in which the movement of the piston rod is converted into the amount of movement of a wire suspended on a pulley, and the position of the wire decelerated by this pulley is detected by an electromagnetic detector.
57-11314), (f) A magnetic material is applied to the slit carved on the surface of the piston rod, a signal of a certain wavelength is recorded on this magnetic material, and the magnetic material is detected by a magnetic head provided on the cylinder side. A device that magnetically detects the amount of movement of the piston rod and converts it into a signal as the stroke amount of the piston rod.
32704) etc. are now available.

However, in the case of (a) above, when the fluid sealed in the cylinder is a liquid medium such as oil, changes in viscosity due to changes in the temperature of the liquid medium, changes in the pressure of the liquid medium, etc. Not only does this have the drawback of causing errors in the detected data, but it also requires a configuration to seal the transceiver from the liquid medium. In addition, in (b), in order to increase the detection sensitivity of the stroke of the piston rod, a large number of light emitting elements and light receiving elements as well as their leads are required, making the assembly complicated and expensive. Ta. In the case of (c), the structure and circuit configuration are complicated, and in the case of (d), there is a problem that the structure is complicated and the detection accuracy is lowered due to deformation of each member. Furthermore, in the case of (e), there is a problem that the amount of movement of the piston rod in and out does not correspond accurately to the amount of movement of the wire due to the expansion and contraction of the wire itself, and in the case of (f), there is a problem that the distance between the magnetic head and the magnetic material is There was a problem in that a gap a was created in the gap a, and this gap loss (5.46a/λ) deteriorated the reproduction sensitivity (signal detection sensitivity). Note that λ is a wavelength, and the shorter the wavelength, the greater the loss.

The present invention solves the various problems of the conventional piston rod, and even though the eddy current sensor, which is the detection part, is disposed on the cylinder side and is separated from the piston rod, which is the detection part, the piston rod position can be determined. The present invention provides a fluid pressure cylinder such as a servo cylinder that can be detected with high sensitivity and can obtain highly reliable detection data without being affected by changes in fluid pressure or viscosity inside the cylinder or by ambient temperature.

For this reason, the present invention provides a plurality of concave and convex surfaces made of a conductive member and arranged in a constant relationship in the longitudinal direction of the outer circumference of the piston rod. By arranging multiple eddy current sensors at a certain distance along the coil, these eddy current sensors can detect the amount of displacement of the uneven surface with high precision as the amount of change in coil impedance. It is.

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 schematically shows a fluid pressure cylinder according to the present invention, in which 1 is a cylinder, 2 is a piston rod that penetrates one sealed end of this cylinder 1 and enters and exits, and 3 is fixed to the second end of this piston rod. The piston 3 is a piston that slides on the inner surface of the cylinder, and a cylinder 4 is attached to the outer periphery of the piston 3.
The outer circumferential surface of the piston rod 2 is coated with ceramic by thermal spraying or the like, so as to provide the cylinder with sufficient heat resistance and wear resistance. 5 is piston rod 2
and a sealing material for sealing one sealed end of the cylinder 1;
Reference numeral 6 denotes an eddy current sensor supported on the cylinder 1 side near where the sealing material 5 is provided, and a long groove 8 in which a plurality of uneven surfaces 7 are arranged in a row in the longitudinal direction of the outer peripheral surface of the piston rod 2 facing the eddy current sensor 6. is engraved. Further, the relationship between the uneven surface 7 and the eddy current sensor 6 is as shown in an enlarged view in FIG.
The eddy current sensor 6 includes a plurality of eddy current sensors 6a, 6
These eddy current sensors 6a, 6b, 6c...6n are arranged so that their detection positions are shifted with respect to the uneven surface arranged at equal intervals. There is. That is, as shown in FIG. 2, when the distances between the rising portions of the convex portions 7a of the uneven surface 7 are equal, each convex portion 7a and each one of the eddy current sensors 6a, 6b, 6c facing the convex portions 7a are the same.
. . 6n, the axial positions thereof are gradually shifted slightly as shown in ε ₀ , ε ₁ , ε ₂ , . . . ε _o .

By the way, this eddy current sensor 6 has a radius γ, for example.
It consists of a coil with an alternating current of angular frequency ω.
i _c is supplied from an oscillator 9 via an output circuit 8. Now, if the electrical conductivity σ, magnetic permeability μ, thickness t, and temperature T of the piston rod 2 forming this uneven surface 7 are given, and the distance from the coil of the eddy current sensor 6 is χ, then An eddy current i _e due to the induced voltage flows, and this eddy current i _e inevitably causes a change in the impedance z of the coil, and this impedance z is a function z = f including χ, σ, μ, t, and T.
(χ, σ, μ, t, T). Therefore, σ, μ,
When t and T are constant, a change in impedance z can be taken as a change in χ, which acts as a displacement sensor using eddy current.
The change in impedance z obtained in this way is input to the calculation circuit 11 via the input circuit 10, where signal processing including predetermined waveform shaping is performed to calculate the displacement amount, that is, the displacement position of the piston rod 2. , will be displayed as necessary.

FIG. 4 shows a specific example of the arithmetic circuit. In the figure, 21a, 21b...21n are signal comparators connected to each of the eddy current sensors 6a, 6b...6n, to which a reference signal of a constant level is input from the reference signal generator 22, Current sensor 6
Comparison outputs with each signal from a, 6b, . . . 6n are taken out. In addition, each signal comparator 21
a, 21b...21n have differentiating circuits 22a, 22b.
...22n and waveform shaping circuits 23a, 23b...2
3n are connected sequentially, and these waveform shaping circuits 23
Each output side of a, 23b . . . 23n is connected to one OR gate 24, which is further connected to a digital counter 25. 26
is a reference level signal generator connected to the signal comparators 21a, 21b...21n, and each eddy current sensor 6
The alternating outputs from a, 6b, . . . 6n are compared with a reference level signal. Further, 27 is a set/reset flip-flop circuit for controlling the counter 25.

Next, the operation of the fluid pressure cylinder and the circuit will be specifically explained.

Now, each eddy current sensor 6a, 6 on the cylinder 1 side
If the piston rod 2 is moved to the left in FIG. 3 with respect to b...6n, the eddy current sensors 6a, 6b...6n will move ε ₀ , ε ₁ , ε ₂ . Since they are installed in a distorted manner as shown in ε _o , they have e ₀ , as shown in Figure 5a.
Out-of-phase sine wave signal voltages such as e ₁ , e ₂ ... e _o are obtained. These voltages are obtained by changing the coil impedance of each sensor. The signal voltage thus obtained is applied to the signal comparator 21.
a, 21b...21n and is compared with a signal e _s of a predetermined level output from the reference level signal generator 26, and the point in time when this signal e _s intersects with the rising portion of each signal e ₁ , e ₂ ... e _o Pulse signals e ₁ ', e _{2 '} . Subsequently, the pulse signals e ₁ ′, e ₂ ′...e _o ′ obtained in this way are applied to the differentiating circuits 22a, 22b...2.
2n to form differential pulses as shown in FIG.
3n, pulses e ₁ ″, e ₂ ″ . . . e _o ″ with small time widths as shown in FIG. 5d are obtained.

Next, these pulses e ₁ ″, e ₂ ″...e _o ″ are input to the OR gate 24, and the output of the OR gate 24 is then output to the counter 25.
5, a counting on/off signal is inputted from the set/reset flip-flop circuit. That is, this counter 25 is, for example, an eddy current sensor 6a.
When the first signal e ₁ is obtained, the counter 25 enters the set state, and the counter 25 is turned on, that is, becomes a countable state. When the next same signal e ₁ is obtained, the counter 25 enters the reset state, and the counter 25 becomes the reset state. Stop counting. This period is L as shown in FIG. 5b, and pulse signals e ₁ ″, e ₂ ″, . . .
e _o ″ is counted.

In this way, a plurality of eddy current sensors 6a,
By using the eddy current sensors 6b...6n, the amount of displacement of the piston rod 2 can be reduced by the number of eddy current sensors 6a, 6b...6n, compared to the case where only one eddy current sensor is provided facing the uneven surface 7. It is possible to detect with high precision, and in the embodiment described above, the precision is improved by n times. In order to improve this accuracy, the detection accuracy can be further improved by downsizing and integrating the eddy current sensors 6a, 6b, . . . , 6n into an integrated block body. In addition, long grooves 20 similar to those described above are formed at different locations on the outer periphery of the piston rod 2 in the longitudinal direction thereof, and uneven surfaces 7 similar to those described above are formed inside these grooves. The eddy current sensors are placed one by one so as to face each other, and _these
The detection accuracy can also be improved by deviating from each other by a predetermined distance such as ε ₁ and ε ₂ . Furthermore, by displacing a plurality of eddy current sensors on each of these uneven surfaces 7 in a constant relationship, it is possible to further improve detection accuracy.

Although not explained in detail, piston rod 2
The displacement direction of the eddy current sensors 6a, 6b...6
It can be measured by electrically detecting that any two outputs of n are in a back-and-forth relationship with each other depending on the direction of displacement of the piston rod 2, and can also be measured using a well-known displacement sensor. It is also possible.

According to this embodiment, by arranging a large number of eddy current sensors 6 in parallel, a sensor with high resolution can be constructed without significantly narrowing the interval between the uneven surfaces 7. .

As explained in detail above, according to the present invention,
A scaled uneven surface made of a conductive material is provided in the longitudinal direction of the outer circumferential surface of the piston rod, and a plurality of eddy current sensors are installed in parallel on the cylinder at a position opposite to this uneven surface, and each of these eddy current sensors is installed next to each other. The eddy current sensor is arranged so that the distance between the piston rods gradually increases or decreases in a constant relationship, and the amount of change in impedance that occurs in the eddy current sensor as the piston rod moves in and out of the cylinder determines whether the piston rod moves in or out of the cylinder. By making it possible to determine the amount (displacement amount), the distance between the uneven surfaces can be reduced significantly.
The amount of displacement of the piston rod can be measured with high resolution, and the amount of displacement of the piston rod can be detected with high accuracy without being affected by changes in fluid pressure in the cylinder, changes in fluid viscosity, or fluid temperature. . In addition, since the detection is possible by installing an eddy current sensor non-contact to the piston rod, mutual wear does not occur.
As a result, there is an advantage that the durability of the entire cylinder device is improved.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway front view showing a specific example of the fluid cylinder of the present invention, Fig. 2 is an explanatory view showing the relationship between the piston rod and the eddy current sensor, and Fig. 3 is an explanatory view showing the relationship in detail. 4 is an example of an arithmetic circuit for measuring the amount of displacement of a piston rod, and FIG. 5 is a time chart of signals from various parts of the arithmetic circuit. 1...Cylinder, 2...Piston rod, 3...
... Piston, 6, 6a, 6b...6n... Eddy current sensor, 7... Uneven surface, 11... Arithmetic circuit.

Claims (1)

[Claims for Utility Model Registration] (1) Detect the amount by which the piston rod moves in and out of the cylinder in response to a control command, and calculate the amount by which the piston rod moves in and out based on the error data between this detected data and the control command data. In a fluid pressure cylinder in which the piston rod is set at a position according to the control command data, an uneven surface made of a conductive member and scaled in the longitudinal direction is provided in the longitudinal direction of the outer peripheral surface of the piston rod, and an uneven surface is provided on the cylinder at a position opposite to the uneven surface. A plurality of eddy current sensors are arranged in parallel, and the distance between adjacent eddy current sensors gradually increases or decreases in a constant relationship in the longitudinal direction, and the piston rod moves in and out. A fluid pressure cylinder configured such that the amount of movement in and out of the piston rod can be determined from the amount of change in coil impedance that occurs in the eddy current sensor. (2) The fluid pressure cylinder according to claim 1, which is provided with scaled uneven surfaces at a plurality of locations on the outer circumferential surface of the piston rod in the longitudinal direction. (3) The fluid pressure cylinder according to claim 1, which is formed by integrating a plurality of eddy current sensors into an integrated block. (4) The fluid pressure cylinder according to claim 1, wherein the piston rod is coated with a ceramic layer on the outer circumferential surface of the piston rod.