JPS6142206B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a configuration of a torque detection spring in a coil spring type rotating body torque measuring device that can eliminate the shift of the torque zero point caused by the rotational speed appearing in the detected torque value.

An induction motor with a built-in torque meter has been developed as a drive machine for monitoring the machining of machine tools, etc., but the method was originally published in Japanese Patent Application No. 53-65223.
The system using a torsion bar as disclosed in No. 1983 has been replaced by a coil spring system (disclosed in Japanese Patent Application No. 145364/1982) which is advantageous in terms of appearance. In the latter coil spring method, the centrifugal force applied to the coil spring changes depending on the rotation speed, which causes torsional displacement of the coil spring and changes in the zero point of torque output, so high-precision torque detection is performed at variable speed. Some measures are required for this.

To explain this phenomenon in more detail, for example, in an induction motor with a built-in coil spring type torque detection device, a torque measuring device using a coil spring 1' as a torque detection spring as shown in FIG. It was built into an induction motor with a similar configuration. In FIG. 1, 2 is a main shaft, which is supported by a motor casing 3 with bearings 4, 4. Needle bearings 5, 5 are located on the outer periphery of the main shaft 2.
The rotor shaft 6 is rotatably supported by. A fixed ring 1'a of the coil spring 1' is attached to the main shaft 2.
is fixed, and a movable ring 1'b of the coil spring 1' is fixed to one end of the rotor shaft 6. First and second detection plates 7 and 8 are attached to the fixed ring 1'a and the movable ring 1'b, respectively, and the circumference of each detection plate has an indexing angle that equally divides the circumference. Salient poles 7a and 8a are formed at the positions. A detection element mounting frame 9 is attached to the motor casing 3, and the first detection element mounting frame 9 is attached to the detection element mounting frame 9.
and each salient pole 7a of the second detection plates 7 and 8,
The first and second detection elements 1 are in close proximity to 8a.
0 and 11 are fixed. In the figure, 12 is a rotor;
13 indicates a stator.

The detection elements 10 and 11 are configured to generate one pulse each time the salient poles 7a and 8a pass,
As is already known, a type that detects changes in magnetic flux, an electromagnetic induction type, an electrostatic induction type, or a photoelectric type can be used.

The error caused by the rotational speed of the coil spring 1' in such a configuration will be explained below.

The centrifugal force F that acts on the unit length of the coil spring wire when the coil spring rotates around its central axis.
is, F=ρSrω ² (however, ρ: density of coil wire [Kg/m ³ ], S: cross-sectional area of coil wire [m ² ], r: radius of coil [m], ω [ rad/sec〕). When the radius of the coil increases by Δr due to this centrifugal force,
The energy per unit length of the wire received by the coil spring is u=1/2ρSrω ² Δr . Now, as shown in Figure 3, the spring wire with a length of 2πr increases from the radius r to the radius (r + Δr), and therefore the angle of the spring wire seen from the central axis changes from 2π to (2π - Δθ). Since the length of the spring wire is constant, 2πr=(2π
-Δθ)(r+Δr) holds true. From this, Δr≒rΔθ/2π Furthermore, if the twist angle per unit length of the wire is Δφ, then Δφ=Δθ/2πr
Therefore, from these two relational expressions, Δr=r ² Δφ ...... The following expression is derived from this expression and the above expression.

u=1/2ρSr ³ ω ² Δφ ...... On the other hand, when the wire is bent by Δφ, the energy u' stored in the wire is expressed by the following formula.

u'=1/2EIΔφ ² ...... However, E is the longitudinal elastic modulus of the coil wire, and I is the second moment of area of the coil wire.

Since the above two energies u and u' are equal, Δφ=ρSr ³ ω ² /EI ...... is established. From this, the twist angle Δθ per revolution of the coil spring is Δθ=2πr ⁴ ρSω ² /EI . For example, if the coil spring wire has a rectangular cross section, and the radial side is h and the axial side is b, then Δθ=24πr ⁴ ρω ² /Eh ² .

When trying to measure torque when the rotational speed changes using a coil spring in this way, the coil itself is twisted by centrifugal force, causing a zero point fluctuation error in the torque meter.

Estimating the magnitude of Δθ for one example, r=35×10 ^-3 m, h=11×10 ^-3 m, ρ=7.8×
10 ³ Kg/m ³ , E=200×10 ⁹ N/m ² , ω=2π×30rad/
sec (=1800 rpm), Δθ=1.3×
10 ^-3 rad (=0.074 degrees).

Changes in the radial direction of the coil spring at both ends are restrained by the fixed ring and the movable ring, so this angular change is small, but if the torsion of the spring due to the torque to be measured is about 1 degree per revolution, the above example This will result in a speed error of several percent.

The present invention, as a measure to eliminate the zero point fluctuation error of a torque measuring device caused by using such a conventional coil spring, has a structure of the coil spring itself in which a right-handed part and a left-handed part are connected, and the number of turns is changed. Assuming that the left and right spring portions have the same diameter, the centrifugal force of the left and right spring portions cancels out the torsion, and the purpose is to eliminate fluctuations in the zero point of torque measurement.

FIG. 4 shows an embodiment of the torque detection spring 1 according to the present invention, in which a right-handed portion 1R and a left-handed portion 1L are connected at the center of the spring 1, and the other ends are connected to fixed rings 1a. and a movable ring 1b. With such a configuration, the directions of loosening of the springs in the right-handed portion 1R and left-handed portion 1L due to centrifugal force are opposite to each other,
The entire spring 1 can cancel out the influence of centrifugal force. Fig. 5 is a graph explaining this relationship, where the vertical axis is the torsion angle Δθ of the spring and the horizontal axis is the rotational angular velocity ω. The torsion angle curve is represented by b, and the combined torsion angle is represented by c.

FIG. 6 is a block diagram showing the configuration of a torque measuring device using the torque measuring spring of the present invention, but this configuration itself can be of the same type as the conventional one. In the figure, pulses or sine waves with a frequency corresponding to the rotational speed of the first detection plate 7 and the second detection plate 8 are output from the first and second detection elements 10 and 11, and the waveform shaping circuit 21, After being shaped into a rectangular wave by 22, the signal is input to a time difference detection circuit 23, which is configured to output an output according to the phase difference between the two detected waveforms. That is, when the load torque increases, the second detection plate 7 on the load side
The rotational phase of the second detection plate 8 lags behind, and conversely, during deceleration, etc., the rotational phase of the second detection plate 8 advances due to the moment of inertia on the load side, and an electric signal corresponding to the phase time difference is transmitted to this time difference detection circuit. 23, it is output together with the sign of its lead/lag. Then, the output is amplified by the next amplifier 24, and by selecting the degree of amplification to a desired value, it is possible to obtain an output converted into a torque value.

As described above, according to the present invention, the torque detection spring has a right-handed portion and a left-handed portion that are arranged in series and have the same number of turns and diameter, so that the zero point of the detected torque due to the centrifugal force of the rotating body is This has the effect that the transmission torque of the belt pulley and motor can be measured with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway sectional view showing the structure of an induction motor with a built-in torque detection device, Fig. 2 is a partially cutaway sectional view showing the structure of a coil spring used in conventional torque detection, and Fig. 3 is a partially cutaway sectional view showing the structure of an induction motor with a built-in torque detection device. FIG. 4 is a partially cutaway side view showing an embodiment of the spring of the present invention; FIG.
The figure is a graph showing the relationship between the rotational speed and torsion angle of the spring of the present invention, and FIG. 6 is a block diagram showing the configuration of the torque measuring device.

Claims (1)

[Claims] 1. A coil spring that has one end fixed to the driving side of a rotating body and the other end fixed to the driven side, and whose transmitted torque is detected based on the magnitude of its torsion angle. A torque detection spring characterized in that the winding portions are arranged in series and have the same number of windings and the same diameter.