JPH06241210A - Piston stop detecting device - Google Patents

Abstract

PURPOSE:To provide a piston stop detecting device capable of certainly detecting the stop of a piston without generating wasteful waiting time even if the stop position of the piston in a cylinder is varied. CONSTITUTION:A magnet ring 14 is attached to a piston 12, and a sensor main body 22 containing a hole element 26 is attached to a cylinder tube 20, moreover a signal output line 30 is connected to a processing unit 36 through an amplifier 32 and an AD converter 34. When the piston 12 is moved and entered within the range R shown by the figure (B), the output voltage 40 of the hole element 26 exceeds the reference level L, thereby the piston detecting signal is turned on. When the piston 12 is stopped within the range R, the output voltage 40 becomes constant from the time of the stop, moreover the rate of change of the output voltage 40 becomes 0. As a result, the conditions under which the piston detecting signal is turned on and also the rate of change of the output voltage is 0 are satisfied, thereby the piston detecting signal is turned on, so that the stop of the piston 12 is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a magnetic field generating means such as a permanent magnet attached to a piston, and the magnetic field detecting means provided in the cylinder detects the magnitude of the magnetic field.
The present invention relates to a piston stop detection device that detects a stop of a piston.

[0002]

2. Description of the Related Art In an automatic processing apparatus or the like, a cylinder mechanism such as an air cylinder is used as an apparatus for holding a work. A device for detecting the position of the piston during the operation of the cylinder mechanism is used for sequence control of the automatic processing device and the like. A specific example of such a piston position detecting device is, for example, Japanese Patent Laid-Open No. 64-6980.
There is an invention of a piston position detection device for a fluid pressure cylinder described in Japanese Patent No. In the piston position detecting device described in this publication, a permanent magnet is attached to the outer peripheral portion of the piston, and the magnetic field generated by the permanent magnet is detected by the magnetic field detecting means provided on the outer peripheral portion of the cylinder, whereby the piston The position is detected. Further, in this piston position detecting device, in order to improve the detection accuracy, the sensitive direction of the Hall element as the magnetic field detecting means is mounted so as to be perpendicular to the moving direction of the piston. As a result, the range in which the piston is detected is narrowed, and the piston position can be detected with higher accuracy.

In an automatic machining apparatus or the like, the stop of the piston is also detected by applying the piston position detecting apparatus. A specific example of such a piston stop detection device will be described with reference to FIGS. 3 and 4. FIG. 3 is a front view showing a work gripping device equipped with a conventional piston stop detection device, and FIG. 4 is a timing chart showing an operation of the work gripping device equipped with a conventional piston stop detection device. In FIG. 3, reference numeral 102 indicates
The work gripping device is attached to the tip of the hand unit 104 of the robot. The work gripping device 102 is mainly composed of a driving device 106 and a pair of gripping claws 108A and 108B that are opened and closed by the driving device 106. The drive device 106 is an air cylinder in which a piston (not shown) contained by compressed air slides. And with the advance and retreat of this piston,
The pair of grip claws 108A and 108B open and close. As a result, the work W can be grasped or released inside the pair of grasping claws 108A and 108B.

As shown in FIG. 3, this drive unit 10
An auto switch 110 is attached to the side surface of 6. The auto switch 110 includes a grip claw 108A,
108B detects the stop of the piston in the air cylinder when the workpiece W is gripped by being driven in the directions of arrows WA and WB, respectively. This auto switch 1
The piston stop detection by 10 is performed on the same principle as the piston position detecting device described in the above publication. That is, a permanent magnet is attached to the outer peripheral portion of the built-in piston, and the magnetic field generated by this permanent magnet is detected by the magnetic field detection means provided in the auto switch 110. Here, the auto switch 110 includes the grip claws 108A, 10A.
8B is attached near the position where the piston stops when the work W is gripped. Therefore, when the work W is gripped and the piston stops, the auto switch 1
The magnetic field detected by the magnetic field detecting means in 10 becomes a predetermined magnitude or more. Accordingly, the piston stop detection signal is output from the auto switch 110 to the control device 112, and the grip of the work W is confirmed.

In such a piston stop detection method, there is a problem in that the piston stop position varies due to the variation in the dimension of the work W. That is, the opening degree of the grip claws 108A and 108B when gripping the work differs depending on the size of the work W, and the stop position of the piston also changes accordingly. Therefore, if the detection range of the piston is narrowed as in the piston position detection device described in the above publication, the stop position of the piston may be out of this detection range. In such a case, the detection range is widened by lowering the level of the magnetic field (output signal) that is determined to be detected according to the expansion of the range of the piston stop position due to the variation in the work size. ing.
That is, as shown in the timing chart of FIG. 4, the opening degree of the gripping claws 108A and 108B when the work W is gripped is determined by the point P1 due to the variation in the work size.
To the point P2. Of these, the grip claw 1
Auto switch 11 so that the position of the piston corresponding to the point P1 where 08A and 108B are most opened is within the detection range.
An output level of 0 is set. As a result, the grip claw 1
When the points P1 are reached while gripping the work W by closing the 08A and 108B, the auto switch 110 is turned on and a signal is output to the control device 112.

However, since the detection range of the auto switch 110 is widened in this way, the grip claw 10
Even if 8A and 108B reach the point P1, the work W may not be gripped yet. Therefore, in order to reliably judge the work grip, as shown in FIG. 4, when the auto switch 110 is kept ON for a certain time T, it is judged that the work is gripped for the first time, and the control device 112 is turned off.
Set to N. As a result, even if the stop position of the piston of the drive device 106 varies due to the variation in the work size, it is possible to detect only when the piston has reliably stopped.

[0007]

However, in the above technique, even after the work W is actually gripped at the point P2 shown in FIG. 4 and the piston is stopped, it is determined that the work is stopped until the time t elapses. Not done. Therefore, during this period, the control device 112 cannot execute the next operation, resulting in an unnecessary waiting time t. In particular, in an automatic processing apparatus or the like, a large number of cylinder mechanisms such as the work gripping apparatus 102 are used, so that the dead time becomes large as a whole and the operating efficiency of the apparatus is significantly lowered. It was In view of this, the present invention provides a piston stop detection device that can reliably detect the stop of a piston without creating a useless waiting time, even if the stop position of the piston in the cylinder varies. With the goal.

[0008]

In order to solve the above problems, the present invention provides a device for detecting the stoppage of a piston that slides in a cylinder, wherein the magnetic field generating means is provided in the piston. A magnetic field detection unit that is provided in the cylinder near the position where the piston stops and that outputs a signal proportional to the magnitude of the magnetic field; and a change that calculates the rate of change in the size of the signal output from the magnetic field detection unit. Rate calculation means, and stop detection signal output means for outputting a stop detection signal when the change rate calculated by the change rate calculation means is zero and the signal output from the magnetic field detection means is equal to or larger than a predetermined magnitude. We have created a piston stop detection device. Here, the change rate of zero includes a value close to zero which is determined to be zero in the signal processing, and does not mean that it is mathematically strictly zero.

[0009]

Now, in the piston stop detection device according to the present invention having the above structure, the magnetic field generating means is provided in the piston,
The cylinder is provided with magnetic field detecting means. The magnetic field detecting means is provided near the stop position of the piston and outputs a signal proportional to the magnitude of the magnetic field. When the piston stops near the magnetic field detecting means, the magnetic field generating means provided on the piston approaches within a predetermined distance from the magnetic field detecting means. As a result, the magnetic field detected by the magnetic field detecting means becomes a predetermined magnitude or more, and the output signal from the magnetic field detecting means becomes a predetermined magnitude or more.
On the other hand, when the piston stops, the distance between the magnetic field generating means and the magnetic field detecting means is also kept constant. Therefore, the magnitude of the magnetic field detected by the magnetic field detecting means is constant, and the magnitude of the output signal from the magnetic field detecting means is also constant. As a result, the change rate of the output signal from the magnetic field detecting means calculated by the change rate calculating means becomes zero. At this time, since the output signal from the magnetic field detecting means is equal to or larger than a predetermined value, the stop detecting signal output means outputs the change signal. A stop detection signal is output. As a result, a stop detection signal is output immediately after the piston stops,
There is no unnecessary waiting time. Moreover, by adding the condition that the rate of change of the output signal from the magnetic field detecting means is zero, it is possible to reliably detect only when the piston actually stops. In this way, even if there are variations in the piston stop position, it is possible to reliably detect the stop of the piston without creating unnecessary waiting time.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment embodying the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an embodiment of a piston stop detection device according to the present invention. FIG. 1A is a diagram showing the overall configuration of the piston stop detection device of this embodiment, and FIG. 1B is a diagram showing the characteristics of the output voltage of the Hall element with respect to the piston position. Figure 1
As shown in (A), the piston stop detection device 2 of this embodiment is provided in an air cylinder mechanism having a cylinder tube 20 and a piston 12 slidably fitted in the cylinder tube 20. The cylinder tube 20 is made of a non-magnetic material, and a magnet ring 14 made of a permanent magnet is attached to the outer circumference of the piston 12 as a magnetic field generating means. Further, the piston rod 10 is fixed to the piston 12, and the piston rod 10
A member (not shown) to be driven is attached to the other end of the.

The sensor body 22 is attached to the outer peripheral portion of the cylinder tube 20 by an attachment tool (not shown) so that the attachment position can be changed. A substrate 24 is fixed inside the sensor body 22. A Hall element 26 is fixed to the lower surface of the substrate 24 as a magnetic field detecting means. The Hall element 26 is formed in a plate shape and is sensitive to a magnetic field in a direction perpendicular to the element surface,
It has a characteristic of outputting a signal voltage according to its strength. The signal output terminal 28 of the hall element 26 is connected to the signal output line 3
It is connected to 0. The signal output line 30 is the sensor body 22.
Is taken out and connected to the arithmetic processing unit 36 via the amplifier 32 and the AD converter 34. The output voltage of the Hall element 26 is amplified by the amplifier 32, converted into a digital signal by the AD converter 34, and then calculated by the arithmetic processing unit 3.
6 is input. The arithmetic processing unit 36 is a computer system centered on a CPU (central processing unit) and a memory device such as a RAM and a ROM, and performs arithmetic processing on an output signal from the Hall element 26.

Next, the characteristics of the signal (output voltage) output from the Hall element 26 will be described with reference to FIG. As shown in FIG. 1 (B), the output voltage 40 of the Hall element 26 becomes a hill-shaped curve symmetrical about the mounting position of the Hall element 26 due to the change of the position of the piston 12. That is, when the center of the piston 12 is located at the point S corresponding to the center of the mounting position of the Hall element 26, the output voltage 40 of the Hall element 26 becomes maximum, and the output voltage 40 increases as the center of the piston 12 moves away from the point S. Decrease. Therefore, when the piston 12 moves and stops near the point S, the output voltage 5
0 has a fixed size corresponding to the stop position. Here, in order to output a signal indicating that the piston 12 has come near the mounting center position (scheduled stop position) S of the Hall element 26, the reference level L of the output voltage is set as shown in FIG. Is set. The reference level L is set so that the variation in the stop position of the piston 12 is surely within the range R of FIG.

The processing of the output voltage of the Hall element 26 in the arithmetic processing unit 36 will be described with reference to FIG. FIG. 2 is an explanatory diagram showing a procedure of calculation processing for the output voltage of the Hall element 26. The process described below
It is executed by the arithmetic processing unit 36 shown in FIG. When the piston 12 enters the range R shown in FIG. 1 (B), the output voltage 50 shown in FIG. 2 (A) exceeds the preset reference level L. As a result, FIG.
The piston detection signal 52 shown in (B) is turned on.
At the same time, as shown in FIG. 2C, the change rate (time differential value) 54 of the output voltage 50 in FIG. 2A is calculated.
Then, when the piston detection signal 52 of FIG. 2 (B) is ON,
When the condition that the output voltage change rate 54 in FIG. 2C is zero is satisfied, the piston stop detection signal 56 shown in FIG. 2D is turned ON.

Now, the procedure for detecting the piston stop in the piston stop detecting device 2 of the present embodiment having the above-mentioned structure will be described with reference to FIGS. 1 and 2.
When the piston 12 moves in the direction of arrow G in FIG. 1 (A), the output voltage 50 gradually increases while increasing the slope, as shown in FIG. 2 (A). As a result, FIG.
The output voltage change rate 54 shown in (C) also gradually increases. Subsequently, as the piston 12 further moves in the direction of arrow G, the output voltage 50 of FIG.
The reference level L is exceeded at the point 50a. As a result, the piston detection signal 52 shown in FIG.
Turns on from 2a. When the piston 12 stops within the range R of FIG. 1 (B), the output voltage 50 becomes a constant value from the stopped point 50b, as shown in FIG. 2 (A). As a result, the output voltage change rate 54 shown in FIG.
Becomes zero at the point 54b. As a result, FIG. 2 (B)
2C is ON, and the output voltage change rate 54 of FIG. 2C is zero, the piston stop detection signal 56 is changed at the point 56b as shown in FIG. 2D. Turns on. In this way, even if the stop position of the piston 12 varies, it is possible to reliably detect the piston stop without creating an unnecessary waiting time.

In this embodiment, the piston stop detection signal 56 is turned on when the output voltage change rate 54 shown in FIG. 2 (C) first becomes zero. However, when the repeating time interval of the signal processing in the arithmetic processing unit 36 is extremely short, the rate of change of the output voltage 50 is instantaneously changed even while the output voltage 50 shown in FIG. 2A is still changing. It may be determined to be zero. In such a case, when the output voltage change rate 54 of FIG. 2 (C) becomes zero continuously by repeating the process twice or more, it is possible to determine that the piston is stopped. As a result, even if the repetition time interval of the output signal processing is made extremely short, it is possible to make a reliable determination of piston stop.

In this embodiment, the Hall element 26 is used as a magnetic field detecting means for outputting a signal proportional to the magnitude of the magnetic field.
However, other magnetic field detecting means such as an MR element may be used. Further, although the example in which the permanent magnet 14 is used as the magnetic field generating means has been described, other magnetic field generating means such as an electromagnetic coil may be used. Structure, shape, size of other parts of piston stop detection device
The material, number, arrangement, etc. are not limited to those in this embodiment.

Further, as an effect peculiar to this embodiment, since the piston 12 and the cylinder tube 20 to which the permanent magnet 14 is attached have the same structure as the cylinder portion of the conventionally used cylinder with an auto switch, the auto switch is The configuration of the present embodiment can be easily realized only by replacing the arithmetic processing unit 36 with the connected Hall element 26. Further, since the hall element 26 is attached to the outer periphery of the cylinder tube 20 so that the attachment position can be changed, the piston 12
Even if there is a large change in the stop position of, there is an advantage that it can be dealt with immediately.

[0018]

According to the present invention, the piston stop detection device for determining the stop of the piston from the magnitude of the detected magnetic field and the change rate thereof is provided by providing the piston with the magnetic field generating means and the cylinder with the magnetic field detecting means. In addition, even if there is a variation in the stop position of the piston, it is possible to reliably detect the stop of the piston without creating an unnecessary waiting time. As a result, the operating efficiency of an automatic processing device or the like in which a large number of cylinder mechanisms are used can be significantly improved, and the piston stop detection device becomes extremely practical.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a piston stop detection device according to the present invention.

FIG. 2 is a diagram showing processing of an output signal in an embodiment of the piston stop detection device.

FIG. 3 is a front view showing a work gripping device to which a piston stop detection device of a conventional example is attached.

FIG. 4 is a timing chart showing the operation of a work gripping device to which a conventional piston stop detection device is attached.

[Explanation of reference numerals] 2 piston stop detection device 12 piston 14 magnetic field generation means 20 cylinder 26 magnetic field detection means 36 change rate calculation means 36 stop detection signal output means

Front page continuation (72) Inventor Takuji Yamada 4-2-2 Kinunodai, Taniwahara-mura, Tsukuba-gun, Ibaraki SMC Tsukuba Technology Center (72) Inventor Takeshi Nakamura 4-chome, Taniwahara-mura, Tsukuba-gun, Ibaraki No. 2 SMC Tsukuba Technology Center

Claims (1)

[Claims] 1. A device for detecting a stop of a piston sliding in a cylinder, comprising magnetic field generating means provided in the piston, and a magnetic field magnitude provided in the cylinder near a position where the piston stops. Magnetic field detecting means for outputting a signal proportional to the magnetic field, change rate calculating means for calculating the change rate of the magnitude of the signal output from the magnetic field detecting means, and the change rate calculated by the change rate calculating means is zero. And a stop detection signal output means for outputting a stop detection signal when the signal output from the magnetic field detection means is equal to or larger than a predetermined magnitude, and a piston stop detection device.