JP2003166887A - Torque detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a torque detection device capable of detecting a torque with stable accuracy. <P>SOLUTION: This torque detection device has a drive shaft 4 rotating by receiving the drive of a motor 3, and an output shaft 7 connected to the drive shaft 4 through a torsionally-deformable coil spring 6. The device also has a casing 2 for specifying the connection length of the drive shaft 4, the coil spring 6 and the output shaft 7 to be constant, and pulse encoders 5, 8 for emitting pulse signals corresponding to the rotation of the drive shaft 4 and the output shaft 7 respectively. The device has a constitution wherein the pulse signals of the pulse encoders 5, 8 are processed by an operation means 9, to thereby determine the rotation angle difference between the drive shaft 4 and the output shaft 7, and a load torque loaded on the output shaft 7 is calculated therefrom. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque detecting device for detecting torque acting on an output shaft.

[0002]

2. Description of the Related Art As a conventional torque detecting device, Japanese Patent Laid-Open No.
A torque detection structure in an automatic screw tightener disclosed in Japanese Patent Laid-Open No. 5-48584 is known. This torque detection structure connects a drive shaft that rotates by receiving the drive of a motor and an output shaft on the driver bit side via a planetary gear mechanism, and a differential of the planetary gear mechanism generated by a torque acting on the driver bit. Therefore, a strain tube that is distorted in the twisting direction is provided. A strain gauge is attached to the surface of this strain tube, and when the strain tube is distorted while a current is applied to this strain gauge, the output voltage of the strain gauge changes according to this distortion. There is. Then, the torque is obtained according to the output voltage of the strain gauge.

[0003]

However, in the above-mentioned conventional torque detection structure, the output voltage fluctuation of the strain gauge is detected and processed.
An A / D conversion circuit for once converting the signal from the strain gauge into a digital signal is required, which causes a problem that the control circuit becomes complicated. Also, the responsiveness of the strain gauge depends on the attachment state (attachment position, amount of adhesive, etc.) to the strain tube, so the attachment work is performed in an elaborate manner in order to obtain highly accurate and stable response. There was a need. Further, in order to cope with the detection of a small torque, it is necessary to make the thickness of the strain tube thinner, but there is also a problem in that there is a limit in processing and thus there is a limit in the torque that can be detected.

[0004]

The present invention has been made in view of the above problems, and includes a drive shaft that rotates by receiving the drive of the rotation drive means, and a twisting member that can be twisted and deformed on the drive shaft. A torque detection device having an output shaft connected via a casing, which defines a connection length of the drive shaft, the torsion member, and the output shaft to be constant, and a signal which emits a signal in response to rotation of the drive shaft. No. 1 angle signal generating means, second angle signal generating means for outputting a signal in response to rotation of the output shaft, and acting on the output shaft based on signals from the first and second angle signal generating means. And a calculating means for obtaining the torque to be applied. It is preferable that the first angle signal generating means and the second angle signal generating means are pulse encoders that generate digital pulse signals in accordance with the rotations of the drive shaft and the output shaft. Further, the calculating means determines each rotational angle of the drive shaft and the output shaft from the signals generated by the first and second angle signal generating means, and the torque acting on the output shaft from the difference between them. Is desirable. Further, the twisting member is preferably made of an elastic member.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a torque detecting device, which has a casing 2 fixed to a member B such as a frame of a machine, and a motor 3 which is an example of a rotation driving means is installed in the casing 2. The member B and the casing 2 are set to have a strength such that they are not deformed by the torque in the range to be detected by the present torque detection device.

A drive shaft 4 which is rotated by receiving the drive of the motor 3 is connected to the motor 3, and a pulse encoder 5 which issues a digital pulse signal of 1 or 0 in response to the rotation of the drive shaft 4 is also provided. It is arranged as an example of first angle signal generating means. A coil spring 6, which is an example of a torsionally deformable torsion member, is connected to the drive shaft 4, and an output shaft 7 is connected to the tip of the coil spring 6. The output shaft 7 is rotatably supported by the casing 2 via a bearing, and is provided so that its tip projects from the tip of the casing 2. The tip of the output shaft 7 has a structure capable of connecting a tool such as a driver bit, which is a tool for tightening a screw, on which torque is applied during work. Also, casing 2
A pulse encoder 8 is provided therein as an example of second angle signal generating means.
Is configured to detect the rotation of the output shaft 7 which is rotatably inserted through the inside and issue a digital pulse signal of 1 or 0.

The drive shaft 4 and the output shaft 7 are supported by the casing 2 in a state that they cannot move in the axial direction,
This realizes a structure in which the connection length of the drive shaft 4, the coil spring 6, and the output shaft 7 is regulated to be constant. With this structure, when a difference in rotation occurs between the drive shaft 4 and the output shaft 7, the coil spring 6 is twisted without being bent (not compressed or stretched). When the output shaft 7 or the drive shaft 4 is allowed to move in the axial direction so as to allow the bending of the coil spring 6 or the casing 2 has a two-part structure so that the casing 2 can slide, torque acts on the output shaft 7. At times, the coil spring 6 is twisted and bent, which causes a force to return the output shaft 7 in the opposite direction. This is a coil spring 6
This phenomenon occurs not only in the case of a member that is twisted and deformed, but when such a phenomenon occurs, when the tightening torque for tightening the screw is detected by the torque detection device 1, the tightening is performed. Torque cannot be detected.
That is, when a general screw is tightened, the screw is screwed into the work, and the tightening torque increases from when the head seat surface is seated on the work. Therefore, if the coil spring 6 is configured to bend, the coil spring 6 bends from this point, and a force for reversing the output shaft 7 is generated accordingly. On the other hand, at this point, the screw is easily loosened, so the output shaft 7 reverses,
The tightening torque cannot be detected accurately. In order to prevent such a phenomenon from occurring, in the present torque detection device 1, the casing 2 defines the connection length of the drive shaft 4, the coil spring 6 and the output shaft 7 to be constant so that the coil spring 6 does not bend even when twisted. It is configured as follows. As a result, even if the coil spring 6 is twisted, the drive torque in the same direction as the rotation direction of the drive shaft 4 can be transmitted to the output shaft 7.

Reference numeral 9 is a calculation means. This computing means 9
Is connected to the pulse encoders 5 and 8 so that the calculating means 9 can process the pulse signals output from the pulse encoders 5 and 8 to obtain the torque acting on the output shaft 7. Has been done.

Next, as shown in FIG. 2, the screw S is attached to the output shaft 7 of the torque detecting device 1 by a screw tightening device which is connected to a driver bit 10 so as to rotate integrally.
The operation of tightening the workpiece W on the workpiece W will be described. First, a screw is engaged with and held by the tip of the driver bit 10. Since the tip of the driver bit 10 is magnetized, the screw S can be attracted and held. Next, the apparatus is moved to position the screw S held at the tip of the driver bit 10 at the tightening position of the work W. When the motor 3 is driven in this state, the drive shaft 4 is rotated in response to this, and the rotation of the drive shaft 4 is transmitted to the output shaft 7 via the coil spring 6. This causes the driver bit 10 and the screw S to rotate together,
The screw S is screwed into the work W. Further, the rotation of the drive shaft 4 and the output shaft 7 causes the pulse encoders 5 and 8 to output pulse signals, which are sent to the computing means 9.

The calculating means 9 counts the pulse signals output from the pulse encoders 5 and 8 and determines the rotation angle of each axis from these count values. Then, the difference between these rotation angles is obtained, and the difference is multiplied by the strain coefficient of the coil spring 6 to calculate the load torque acting on the output shaft 7. When this is expressed by a mathematical formula, it becomes as shown in Formula 1.

[Equation 1] The strain coefficient K is a proportional constant determined by the strength of the coil spring 6, and is subjected to a test in advance to obtain a rotation angle difference (θ1-θ).
It is determined from the result of comparison between 2) and the actual load torque applied to the output shaft.

When the screw head seat surface is seated on the work, the tightening torque increases thereafter, and a rotational load, that is, a load torque is applied to the output shaft 7 side in accordance with this tightening torque. Therefore, the coil spring 6 is twisted to a certain degree, and in accordance with this twist, a difference occurs between the rotation angles of the drive shaft 4 and the output shaft 7 obtained from the pulse signals of the pulse encoders 5 and 8. At this time, as the tightening torque of the screw S increases, the twist angle of the coil spring 6 increases, so that the rotation angle difference also increases in proportion to the tightening torque.
Therefore, the load torque calculated in real time by the calculating means 9 will increase. The rotation speed of the motor 3 is controlled according to the load torque calculated by the calculation means 9, and the drive is stopped when the load torque reaches a predetermined screw tightening completion torque. In this state, the motor 3 is locked and held for a predetermined time so that the drive shaft 4 cannot rotate, and the torque generated from the twist of the coil spring 6 is applied to the screw S. This makes it possible to tighten the screw with a predetermined torque while reducing the impact on the screw S. Next, the motor 3 is reversely driven until the difference in rotation angle between the pulse encoders 5 and 8 becomes 0 (zero). As a result, the coil spring 6 returns to its original shape without twist. After that, the device is detached from the screw S, and a series of screw tightening work is completed. .

In the embodiment of the torque detecting device according to the present invention described above, the coil spring 6 is adopted as an example of the twisting member, but in addition to this, a rod-shaped or plate-shaped member which can be twisted and deformed. An elastic member such as a spring material or rubber may be used as the twisting member. Thus, even if a twisting member other than the coil spring 6 is adopted, the same effect can be obtained. Further, when the torque to be detected is set in a relatively large range, a similar effect can be obtained even if a thin member such as a conventional strain tube is adopted as the twisting member.

[0013]

The torque detecting device according to the present invention regulates the connecting length of the drive shaft, the twisting member and the output shaft to a fixed length by the casing, and outputs a signal according to each rotation of the drive shaft and the output shaft. An angle signal generating means such as a pulse encoder for emitting light is provided. Therefore, it is possible to detect the rotation angle difference between the drive shaft and the output shaft when load torque acts on the output shaft while the drive shaft to the output shaft are rotating. You can know the torque that is acting. Therefore, it is not necessary to use a strain gauge as in the conventional torque detection structure, and there is an advantage that torque can be detected with stable accuracy with a structure that is relatively easy to assemble. Further, since the angle signal generating means is a pulse encoder that outputs a digital signal, the A / D converter is not required in the arithmetic means for processing this signal, the circuit configuration can be simplified, and the A / D There is an advantage that a loss due to conversion can be eliminated and a highly accurate responsiveness can be secured. In addition, since the twisting member is made of an elastic member such as a spring material, it is possible to select one with various elastic coefficients compared to the conventional strain tube, and it is possible to easily detect smaller torque. become able to. Therefore, by adopting a screw tightening device etc. for tightening screws that have been miniaturized recently,
There is an advantage that it is possible to detect the minute screw tightening torque which has been difficult in the past. This effect becomes even more remarkable by adopting a pulse encoder as the angle signal generating means to improve the responsiveness.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a torque detection device according to the present invention.

FIG. 2 is an explanatory sectional view showing a usage state of the torque detection device according to the present invention.

[Explanation of symbols]

1 Torque detection device 2 casing 3 motor 4 drive shaft 5 pulse encoder 6 coil spring 7 Output shaft 8 pulse encoder 9 computing means 10 driver bits

Claims (4)

[Claims] 1. A torque detection device having a drive shaft that rotates upon receiving the drive of a rotation drive means, and an output shaft that is connected to the drive shaft via a torsionally deformable torsion member. A casing that regulates the connection length of the twisting member and the output shaft to be constant; a first angle signal generating unit that outputs a signal according to the rotation of the drive shaft; and a first angle signal generating unit that outputs a signal according to the rotation of the output shaft. A torque detecting device comprising: two angle signal generating means; and a calculating means for obtaining a torque acting on the output shaft based on signals from the first and second angle signal generating means. 2. The first angle signal generating means and the second angle signal generating means are pulse encoders for respectively generating digital pulse signals according to the rotation of the drive shaft and the output shaft. Item 2. The torque detection device according to item 1. 3. The calculating means obtains the respective rotation angles of the drive shaft and the output shaft from the signals generated by the first and second angle signal generating means, and the torque acting at the time of output from the difference between them. The torque detection device according to claim 1 or 2, wherein 4. The torque detecting device according to claim 1, wherein the twisting member is an elastic member.