JP2000314666A - Torque measuring device - Google Patents

Abstract

(57) [Problem] To enable accurate measurement of torque over a wide measurement range with a small measuring device even if a transmission shaft on which torque acts is short. When torque is transmitted from a driving shaft (3A) to a driven shaft (3B), an elastic body (7) interposed between a pair of couplings (4A, 4B) connecting the driven shaft and the driven shaft (3B) moves in a rotational direction. Because of the expansion and contraction, a large relative angular displacement can be generated even if the axis for transmitting the rotational force is short, and the torque can be accurately detected based on the angular displacement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque measuring device for measuring a torque transmitted from a driving rotating body whose center of rotation is arranged coaxially to a driven rotating body.

[0002]

2. Description of the Related Art A torque measuring device is used for detecting and displaying a torque transmitted through a transmission shaft or the like during transmission between a prime mover and a working machine, and adjusting the output of the prime mover according to the torque. . Recently, a torque measuring device has been used to automatically turn on and off an electric motor of an electric assist bicycle. This torque measuring device constantly monitors the torque of the crankshaft, and automatically starts the electric motor when the pedal becomes heavy and the torque exceeds a certain value, for example, when going up a hill. It is made as follows.

There are contact type and non-contact type torque measuring devices of this type, and the non-contact type includes a magnetostrictive type and a phase difference type. The contact type torque measuring device is a device in which a strain gauge is attached to the surface of a transmission shaft to detect a shear strain on the surface of the transmission shaft caused by a torque, and the shear strain is output to the outside via a slip ring and detected. In addition, the magnetostrictive torque measuring device detects a change in magnetic force generated when the magnetostrictive material applied to the surface of the transmission shaft is distorted by torque as a change in inductance of a detection coil disposed on the outer periphery thereof ( See JP-A-9-159551). Further, the phase difference type torque measuring device is equipped with a pulse generator which outputs a pulse signal corresponding to the rotation angle of the transmission shaft at predetermined intervals along the axial direction, and when the transmission shaft is twisted by the torque, each pulse is generated. The torque is measured based on the phase difference between the pulse signals output from the generator.

[0004]

However, both the contact type and magnetostrictive torque measuring devices described above detect the shear distortion of the transmission shaft when a torque is applied, and the transmission shaft has a mechanical strength. And the shear strain is extremely small, there is a problem that the change in resistance and the change in magnetic force are small and the detection accuracy is not improved.

When detecting a change in the magnetic force of the magnetostrictive material as a change in the inductance of the coil, the area of the magnetostrictive material with respect to the cross-sectional area of the coil is very small. However, there is also a problem that it is complicated, the cost increases, and an error easily occurs.

Further, in the phase difference type torque measuring device, since the torsion of the transmission shaft is detected as a relative angular displacement, a large angular displacement cannot be obtained unless the transmission shaft is lengthened. However, there is a problem that the size must be increased.

[0007] Therefore, it is a technical object of the present invention to provide a small-sized and capable of accurately and accurately measuring torque over a wide measuring range.

[0008]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a method for generating a torque based on a relative angular displacement generated between a driving rotating body and a driven rotating body whose rotation centers are coaxially arranged. In the torque measuring device for measuring, the driving rotator and the driven rotator are connected via a pair of couplings, and an elastic body having one end attached to the driving side and the other end attached to the driven side between the couplings. The elastic body is expanded and contracted in a rotational direction by a rotational force transmitted from a driving side to a driven side to generate a relative angular displacement between the rotating bodies.

According to the present invention, an elastic body which expands and contracts in the direction of rotation by a rotational force transmitted from the driving side to the driven side is interposed between a pair of couplings connecting the driving rotator and the driven rotator. Therefore, when torque is transmitted to the driven rotating body, the elastic body expands and contracts, and a large relative angular displacement occurs between the driving rotating body and the driven rotating body. Therefore, a large relative angular displacement can be generated even if the shaft transmitting the rotational force is short, and the torque can be detected with high accuracy.

At this time, if a giant magnetostrictive rod is used as the elastic body, the elastic constant is about 1/3 of that of a normal metal material. It can be detected with high accuracy. Also, if a predetermined magnetic bias is applied, the load and the displacement are proportional to a wide range of load,
The torque can be accurately measured based on the phase difference.

Further, if a pulse generator such as a rotary encoder for outputting a pulse signal corresponding to the rotation angle is attached to each of the driving rotator and the driven rotator, the relative angular displacement of each rotator can be changed by each pulse generation. The torque is output as a phase difference between the respective pulse signals output from the device, so that the torque can be measured based on the output. In this case, even if the interval between the pulse generators is reduced, the elastic body interposed between the couplings expands and contracts greatly, and the torque can be measured accurately, so that the measuring device itself can be downsized.

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 is an exploded view showing a torque measuring device according to the present invention, FIG. 2 is a sectional view showing an engaged state of a coupling, FIG. 3 is a graph showing stress-strain characteristics of a giant magnetostrictive rod, and FIG. FIG. 5 is a diagram showing a pulse signal in a state, FIG. 5 is a diagram showing a pulse signal when a load is applied, and FIG. 6 is an explanatory diagram showing an arithmetic processing unit.

The torque measuring device 1 shown in the present embodiment has a driving shaft (driving rotating body) 3 having rotation centers 2A and 2B coaxially arranged.
A torque is measured based on a relative angular displacement generated between the motor A and a driven shaft (driven rotating body) 3B. The driving shaft 3A and the driven shaft 3B are connected via a pair of couplings 4A and 4B. ing.

The couplings 4A and 4B are formed with substantially semicircular projections 5A and 5B that engage with each other, and each of the projections 5A and 5B has a cutout 6A and 6B at one end side facing each other.
B is formed, and an elastic body 7 having one end attached to the notch 6A on the driving side and the other end attached to the notch 6B on the driven side is attached.

The elastic body 7 has a driven shaft 3B
Is driven, a compressive load is applied between the notches 6A and 6B and contracts in the rotational direction, thereby causing a relative angular displacement between the driving shaft 3A and the driven shaft 3B. Therefore, it is desirable to use an elastic body 7 whose longitudinal strain changes linearly without hysteresis when a compressive load corresponding to the torque is applied within the measurement range of the torque. A giant magnetostrictive rod 8 to which a bias is applied is used.

More specifically, the elastic body 7 is formed of a giant magnetostrictive rod 8, a bias magnet 9 for magnetically saturating the rod, and a yoke 10. The giant magnetostrictive rod 8 is made of a giant magnetostrictive material composed of a rare earth element R and iron Fe and having a crystal structure of an RFe ₂ Laves phase type. As the rare earth element R, terbium (Te), dysprosium (Dy),
A material composed of at least one kind of substance of samarium (Sm) and holmium (Ho) and having a composition selected at a ratio of one atomic equivalent of a rare earth element to two atoms of iron is used. In this example, Tb _0.3 ETREMA T based on Dy _0.7 Fe ₂
ERFENOL-D (trademark of Etrimer) is used.

Since TERFENOL-D has an elastic constant of about 1/3 that of a normal metal material, it is greatly distorted even under a slight load, and has a wide range if used in a state of magnetic saturation. It is suitable for measuring torque accurately over a wide range because it deforms linearly without hysteresis in a wide elastic deformation range. Also excellent in nature.

The size of the giant magnetostrictive rod 8 is determined by the torque to be measured, and in this example, its length is about 1c.
m and the cross-sectional area are selected to be about 2.5 cm ² . For example,
If the maximum detected torque is 50 kgfm and the mounting position of the elastic body 7 is 50 mm in radius, a force of 1000 kgf is applied to the elastic body 7. Giant magnetostrictive rod 8 used in this example
When magnetic saturation is performed at 2000 Oe, the strain changes linearly without hysteresis up to a pressure range of 40 MPa as shown in FIG. Here, when the sectional area is selected so that the pressure becomes 40 MPa when a force of 1000 kgf is applied, the sectional area is about 2.5 cm ² . The strain at this time is about 1000 ppm, and when a giant magnetostrictive rod 8 having a length of 1 cm is used, a displacement of 10 μm can be obtained.
A relative angular displacement of about 0.01 ° occurs between B, and this angle can be sufficiently measured by means described later.

The biasing magnet 9 is made of a NeFeB magnet or an SmCo magnet so that a magnetic field (for example, about 2000 Oe) sufficient to magnetically saturate the giant magnetostrictive rod 8 is obtained.
Magnets are used. When using a NeFeB magnet,
If the cross-sectional area is about 12.3 cm ² and the length is about 3 cm, 2000
A magnetic field of Oe can be obtained. In this example, two pieces each having a length of about 1.5 cm are used so as to have a total length of 3 cm, and are disposed so as to sandwich the giant magnetostrictive rod 8.

Further, the yoke 10 is formed of low carbon steel or permalloy, and has a frame 10A having one end opened.
And a slider 10 slidably contacting the opening.
B together with the giant magnetostrictive rod 8 and the bias magnet 9 form a closed magnetic circuit.

A rotary encoder (pulse generator) 1 for outputting a pulse signal corresponding to the rotation angle for detecting the relative angular displacement is provided on the driving shaft 3A and the driven shaft 3B.
1A and 11B are attached. The rotary encoders 11A and 11B are formed at equal pitches along the circumferential direction when the code disks 12A and 12B rotate and the code disks 12A and 12B integrally mounted on the shafts 3A and 3B. Photointerrupters 14A and 14B whose optical path is interrupted by the slits 13
Consists of

Each of the photointerrupters 14A and 14B is adapted to output the respective pulse signals P _A and P _B synchronously when the displacement of the elastic body 7 is maintained at 0 (see FIG. 4). The mounting position has been adjusted. When a load is applied to the driven shaft 3B driven by the driving shaft 3A to cause a compressive displacement of the elastic body 7, each of the shafts 3A, 3B
Code disks 12A, 12 integrally attached to
Since the relative angular displacement occurs between B and B, the pulse signals P _A and P _B output from the photointerrupters 14A and 14B generate a phase difference φ (see FIG. 5).

FIG. 6 shows an arithmetic processing unit 20 for calculating the torque based on the pulse signals P _A and P _{B. The} arithmetic processing unit 20 calculates the torque based on the pulse signals P _A and P _B output from the photointerrupters 14 A and 14 _B. A pulse phase difference detecting means 21 for detecting the phase difference φ, and a torque calculating means 22 for calculating a torque from a preset relationship between the torque and the pulse phase difference.
It has.

The pulse phase difference detecting means 21 comprises a differential amplifier 23 composed of an operational amplifier and an integrating circuit 24 having a time constant RC. To explain on the basis of these input and output pulse signals in FIG. 5, the differential amplifier circuit 23, the pulse signal P _A positive phase input terminal and the negative phase input terminal, the P _A -P _B by inputting P _B is calculated, the pulse signal P _C with a pulse train of the phase difference φ to the output terminal is output. Then, by inputting the pulse signal P _C to the inverting input terminal of the integrating circuit 24, since the signal P _D of the voltage V ₀ which is proportional to the phase difference φ to the output terminal is output, the voltage value V ₀ The phase difference φ is further obtained.

Further, since the phase difference φ and the torque T are calculated by the equation (1), the torque calculating means 22 calculates the torque based on this equation. T = [r ² · At / (Et · L)] sinφ (1) Et: Longitudinal modulus of TERFENOL-D L: Length of TERFENOL-D r: Length of TERFENOL-D from the rotation center Radius to mounting position At: Cross-sectional area of TERFENOL-D

[0026] For example, the phase difference φ is 0.01 ° corresponding to the maximum torque Tmax = 50kgfm, when the voltage V ₀ which signal P _D at that time is 1V, the detection accuracy of the voltage if 1 mV, the phase difference φ can be detected with an accuracy of 0.00001 °. Here, since sin φ ≒ φ (φ ≒ 0), the torque T can be measured with an accuracy of 0.05 kgfm.

The above is an example of the configuration of the present invention, and its operation will be described below. The coupling 4A attached to the driving shaft 3A and the coupling 4B attached to the driven shaft 3B are engaged, and the notches 6A and 6B are fitted with the elastic members 7 incorporating the giant magnetostrictive rods 8 in these notches 6A and 6B. .

Since the elastic member 7 is sandwiched between the notches 6A and 6B, when the driving shaft 3A is driven, the notch 6A of the coupling 4A pushes one end of the elastic member 7 by its rotational force. The other end of the elastic body 7 pushes the notch 6B of the coupling 4B, and the driven shaft 3B is rotated.

Therefore, when a rotational force of the driving shaft 3A is transmitted to the driven shaft 3B, if a load is acting on the driven shaft 3B, a torque corresponding to the load is generated, and the torque is interposed between the notches 6A and 6B. Since a compressive load corresponding to the torque acts on the elastic member 7 thus contracted, the elastic member 7 contracts in accordance with the torque, causing a relative angular displacement between the driving shaft 3A and the driven shaft 3B.

The elastic body 7 is magnetically saturated.
Since a giant magnetostrictive rod 8 having a predetermined size is used,
Up to a compression stress of 40 MPa corresponding to the maximum measured torque.
Longitudinal distortion changes linearly without any stiction. Accordingly
When the elastic body 7 contracts, the driving shaft 3A and the driven shaft 3B
Code disks 12A, 12 integrally attached to
A relative angular displacement corresponding to the torque occurs between B and
Pulse signals P output from the interrupters 14A and 14B
_A, P _BA phase difference φ corresponding to the torque is generated between them (see FIG. 5).
reference).

Next, the two pulse signals P _A and P _B
Is input to the arithmetic processing unit 20, the phase difference φ is detected by the differential amplifier circuit 23 and the integrating circuit 24 of the pulse phase difference detection means 21, and the torque T is calculated by the torque calculation means 22 based on the pulse phase difference φ. Is calculated.

The rotary encoders 11A, 11A
B is not limited to the light transmission type, but may be a light reflection type. Further, a pulse generator that optically, magnetically, and electrically detects a magnet disposed around the driving shaft 3A and the driven shaft 3B, a projection of a gear formed integrally, and the like is used. Is also good. Furthermore, the elastic body 7 has a driving shaft 3A.
Is provided so that a compressive force is exerted thereon, but it may be a case where it is provided such that it is pulled by the driving shaft 3A to exert a tensile force.

[0033]

As described above, according to the present invention, the elastic body is expanded and contracted in the rotational direction by the rotational force transmitted from the driving side to the driven side, and the relative angle between the driven rotating body and the driven rotating body is increased. Since the displacement is generated, a large relative angular displacement can be generated even if the distance for transmitting the rotation is short, and therefore, a very excellent effect that the accuracy of torque measurement is improved. Having.

Further, TERFENOL-D is used as the elastic body.
If you use a giant magnetostrictive rod such as
With a wide elastic deformation range and moderate stiffness, not only can a wide range of torque be measured accurately, but also the response time of strain to a load change is extremely short, a few microseconds, so high-speed response is also possible. There is an effect of being excellent.

[Brief description of the drawings]

FIG. 1 is an exploded view showing a torque measuring device according to the present invention.

FIG. 2 is a sectional view showing an engagement state of the coupling.

FIG. 3 is a graph showing stress-strain characteristics of a giant magnetostrictive rod.

FIG. 4 is a diagram showing a pulse signal in a no-load state.

FIG. 5 is a diagram showing a pulse signal when a load is applied.

FIG. 6 is an explanatory diagram illustrating an arithmetic processing device.

[Description of Signs] 1... Torque measuring device 2A, 2B... Rotation center 3A... Drive shaft (drive rotor) 3B. Drive shaft (drive rotor) 4A, 4B. 6A, 6B Notch 7 Elastic body 8 Giant magnetostrictive rod 9 Bias magnet 10 Yoke 11A, 11B Rotary encoder (pulse generator) 20 Calculation Processing device 21 ・ ・ ・ Pulse phase difference detecting means 22 ・ ・ ・ Torque calculating means

Claims (5)

[Claims] 1. A torque measuring device for measuring a torque based on a relative angular displacement generated between a driving rotating body (3A) and a driven rotating body (3B) whose rotation centers (2A, 2B) are coaxially arranged. In the above, the driving rotator (3A) and the driven rotator (3B) are connected via a pair of couplings (4A, 4B), and one end is located between the couplings (4A, 4B) on the driving side. An elastic body (7) having the other end attached to the driven side is interposed, and the elastic body (7) is expanded and contracted in the rotational direction by a rotational force transmitted from the driving side to the driven side, thereby forming each of the rotating bodies (3A, 3B) A torque measuring device characterized in that a relative angular displacement is caused between them. 2. The torque measuring device according to claim 1, wherein a giant magnetostrictive rod (8) to which a predetermined magnetic bias is applied is used as said elastic body (7). 3. A NeFeB magnet or an SmCo magnet is used as the bias magnet (9) of the giant magnetostrictive rod (8), and the bias magnet (9) and the yoke (10) are used.
3. A torque measuring device according to claim 2, wherein a closed magnetic circuit is formed by said giant magnetostrictive rod. 4. A driving rotator (3A) and a driven rotator (3B).
Each of which is provided with a pulse generator (11A, 11B) for outputting a pulse signal at a cycle corresponding to a rotation angle, and the respective pulses when the driven rotating body (3B) is rotated by the driving rotating body (3A). Pulse phase difference detecting means (21) for detecting the phase difference based on the respective pulse signals output from the generators (11A, 11B), and the torque is calculated from a preset relationship between the torque and the pulse phase difference. Torque calculation means (2
4. The torque measuring device according to claim 1, wherein the torque measuring device comprises: 5. The torque measuring device according to claim 4, wherein said pulse generator is a rotary encoder (11A, 11B).