JP2008075783A - Ultrasonic motor transmission using differential gears - Google Patents

Abstract

An object of the present invention is to improve speed control and trajectory followability of a manipulator that requires an ultrasonic motor from non-magnetic required specifications by expanding the low speed limit of an ultrasonic motor with narrow speed selectivity.
SOLUTION: A first gear driven by a first ultrasonic motor, a second gear driven by a second ultrasonic motor, one or more third gears meshing with the first gear and the second gear, The speed of the first ultrasonic motor is reduced by the movement of the second ultrasonic motor by the differential gear consisting of the output shaft driven by the revolution of the third gear. And realize the same speed as that obtained by combining the motion of the first ultrasonic motor and the motion of the second ultrasonic motor.
[Selection] Figure 1

Description

  The present invention relates to an apparatus for transmitting power of an ultrasonic motor.

  An ultrasonic motor is a motor based on the driving principle of vibration of a piezoelectric element, and is greatly different from a conventional motor that generates a driving force by electromagnetic action. Therefore, it is suitable for applications in which magnetic noise and electromagnetic noise accompanying a large current are avoided, such as an MRI compatible manipulator.

  MRI (Magnetic Resonance Imaging) is a device that takes a tomographic image of a living body using a precise and powerful magnetic field. An MRI compatible manipulator is a manipulator that operates inside the MRI, and is expected to support surgical operations performed mainly within the MRI. Since an MRI compatible manipulator is required to be non-magnetic without disturbing the magnetic field of the MRI, the ultrasonic motor is an optimal motor, and is also a preferred application example for an ultrasonic motor.

  An ultrasonic motor uses the vibration principle of a piezoelectric element as a driving principle. Therefore, it is often driven in the vicinity of a resonance frequency at which a large amplitude can be obtained efficiently. Since the drive frequency and the drive speed are in a strong proportional relationship, if the drive frequency is limited to the vicinity of the resonance frequency, the result is that the drive speed is narrowed or the efficiency other than the rated speed is remarkably deteriorated. Occurs. Therefore, an ultrasonic motor has not only a limitation on high speed but also a limitation on low speed, and the speed selectivity is narrow.

  Therefore, a manipulator using an ultrasonic motor is suitable for point-to-point position control that moves from the starting point to the destination without controlling the moving speed and trajectory. It is not suitable for following the trajectory. For example, a master / slave type manipulator that is a typical surgical support manipulator is required to smoothly reproduce a certain movement of an operator. Such a manipulator requires speed control capable of realizing from low speed to high speed. Alternatively, when a circular motion is performed on the XY stage, an accurate circle cannot be drawn unless the X axis can generate an infinitely small velocity with respect to the Y axis at 0 and 180 degrees. Thus, if the speed selectivity is narrow, accurate trajectory tracking cannot be performed. In other words, it is a very important performance for manipulators that require speed control and trajectory tracking. is there.

  If you just want to lower the low speed limit, you can consider using a speed reducer, but in this case the high speed limit will also decrease, so the speed selectivity is still narrow. A transmission that changes the gear ratio according to the required speed increases speed selectivity, but the mechanism for changing the gear ratio is complicated.

As described in Non-Patent Document 1, the differential gear proposed in the present invention is a widely known transmission. Automotive differentials are the most well-known application and are used to distribute power to two shafts with different speeds. In addition, it is used to generate two orthogonal axes of motion from opposing two-axis power sources such as a bevel gear differential gear that obtains the resultant force of two power sources. However, none of the differential gears were used to expand the speed selectivity of the ultrasonic motor. In addition, although the apparatus which synthesize | combines manual input and an ultrasonic motor as an automatic focus mechanism of a camera is described in following patent document 1 and 2, since these cannot obtain arbitrary deceleration states, the above manipulators It cannot be used to drive the XY stage.
Hiroshi Makino and Masaharu Takano “Mechanical Kinematics”, Corona, 1978 JP 2000-74160 A JP 2000-147360 A

  By expanding the low speed limit of the ultrasonic motor, the speed selectivity is expanded, thereby improving the speed control and trajectory tracking of manipulators, XY stages, etc. that require the ultrasonic motor from the non-magnetic requirement specifications.

  In order to solve the above problems, the present invention provides a first gear driven by a first ultrasonic motor, a second gear driven by a second ultrasonic motor, and a single gear meshing with the first gear and the second gear. The movement of the first ultrasonic motor is changed by the differential gear consisting of a plurality of third gears and an output shaft that is integrated with the rotation shaft of the third gear and driven by the revolution of the third gear. The low speed is realized by canceling with the same, and the same speed as that obtained by itself is realized by combining the motion of the first ultrasonic motor and the motion of the second ultrasonic motor. The same applies if the roles of the first ultrasonic motor and the second ultrasonic motor are interchanged.

  By adopting the above-described method, the present invention can output a speed lower than the low speed limit of each ultrasonic motor by moving in a direction in which the two ultrasonic motors cancel each other. If the two motors move in the same direction, the average speed of the two motors is output. Therefore, when both are driven at the same high speed limit, the same speed is output.

  In the present invention, the load is distributed to the two ultrasonic motors. Therefore, when the two ultrasonic motors are equivalent, the torque that can be generated by this mechanism is twice the torque of the single ultrasonic motor. Therefore, not only can the speed selectivity be increased, but the resultant torque can be obtained.

  An embodiment of a transmission device for an ultrasonic motor using a differential gear according to the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment in which a transmission device for an ultrasonic motor using a differential gear according to the present invention is constituted by a bevel gear. The state before each component is assembled and the state after it is assembled are shown. In the assembly drawing, elements other than the main shaft are shown in a cut model.

  The first ultrasonic motor is composed of a first ultrasonic motor stator 1 and a first ultrasonic motor rotor 2, and the first ultrasonic motor stator 1 is fixed to the base portion and is subjected to vibration generated by the first ultrasonic motor stator 1. One ultrasonic motor rotor 2 rotates relative to the first ultrasonic motor stator 1. The first gear 3 is a bevel gear and is fixed to the first ultrasonic motor rotor 2 and integrally rotates. In FIG. 1, the first shaft 4 serves as the rotation axis of the first ultrasonic motor rotor 2 and the first gear 3. The first shaft 4 can freely rotate with respect to the first ultrasonic motor stator 1, and the first ultrasonic motor rotor 2 and the first gear 3 can freely rotate around the first shaft 4.

  The second ultrasonic motor is composed of a second ultrasonic motor stator 5 and a second ultrasonic motor rotor 6, and the second ultrasonic motor stator 5 is fixed to the base, and the second ultrasonic motor stator 5 is driven by vibration generated by the second ultrasonic motor stator 5. The two ultrasonic motor rotors 6 rotate with respect to the second ultrasonic motor stator 5. The second gear 7 is a bevel gear and is fixed to the second ultrasonic motor rotor 6 and rotates integrally therewith. In FIG. 1, the second ultrasonic motor rotor 6 and the second gear 7 are rotated by the second shaft 8. The second shaft 8 can freely rotate with respect to the second ultrasonic motor stator 5, and the second ultrasonic motor rotor 6 and the second gear 7 can freely rotate around the second shaft 8.

  The third gear 9 is a bevel gear and meshes with the first gear 3 and the second gear 7 as shown in the assembly drawing at the lower right of FIG. The first gear 3 is held by the first ultrasonic motor stator 1, the second gear 7 is held by the second ultrasonic motor stator 2, and the third gear 9 is held by the clasp 11 to maintain mutual engagement.

  The third gear 9 can freely rotate around the third shaft 10. The first shaft 4, the second shaft 8, and the third shaft 9 are integrated. The 1st axis | shaft 4 and the 2nd axis | shaft 8 are coaxial, and do not inhibit mutual rotation. The third axis 10 intersects the first axis 4 and the second axis 8 perpendicularly.

  As a result, the third gear 9 rotates around the third shaft 10 while meshing with the first gear 3 and the second gear 7, and revolves around the axis formed by the first shaft 4 and the second shaft 8. Due to the revolution of the third gear 9, the output shaft 12 formed by the first shaft 4, the second shaft 8, and the third shaft 9 rotates around the shaft formed by the first shaft 4 and the second shaft 8.

  For example, when the first gear 3 and the second gear 7 have the same number of teeth, and the first gear 3 and the second gear 7 rotate at the same speed in opposite directions, the third gear 9 rotates at the same place, and the output shaft 12 Does not rotate. In this state, the rotational motion of the first ultrasonic motor is completely offset by the rotational motion of the second ultrasonic motor.

  For example, when the first gear 3 and the second gear 7 have the same number of teeth, when the first gear 3 and the second gear 7 rotate in the opposite directions and the first gear 3 rotates slightly faster, the third gear 9 becomes the first gear. 3 and the second gear 7 revolve in the same direction as the first gear 3 at half the speed difference, and the output shaft 12 also rotates in the same speed direction. For example, even if the low speed limit of the first ultrasonic motor and the second ultrasonic motor is 30 rpm, the rotation of (32-30) / 2 = 1 rpm is obtained by rotating one at 32 rpm and the other at 30 rpm. I can do it.

  For example, when the first gear 3 and the second gear 7 have the same number of teeth and the first gear 3 and the second gear 7 rotate at the same speed in the same direction, the third gear 9 does not rotate and the first gear 3 And the second gear 7 revolves in the same speed direction, and the output shaft 12 also rotates in the same speed direction.

  For example, when the first gear 3 and the second gear 7 have the same number of teeth, the load applied to the output shaft 12 is evenly distributed to the first ultrasonic motor and the second ultrasonic motor via the first gear 3 and the second gear 7. Distributed. Therefore, the torque that can be generated by this transmission device is twice the torque of the ultrasonic motor alone.

  FIG. 2 shows an embodiment in which the transmission device for an ultrasonic motor using a differential gear according to the present invention is constituted by a spur gear. The ultrasonic motor is omitted to focus on the movement of the differential gear.

  The first gear 15 is a spur gear and is driven by a first ultrasonic motor. The axis is defined as a first axis 16.

  The second gear 17 is a spur gear and is driven by a second ultrasonic motor. The axis is referred to as a second axis 18.

  The third gear 19 is a spur gear and meshes with the first gear 15 and the second gear 17. The first gear 15 is a sun gear, the second gear 17 is an outer ring gear, and the third gear 19 is a planetary gear that is a planetary gear.

  The third gear 19 can freely rotate around the third shaft 20. The third shaft 20 is integrated with the output shaft 22. The first shaft 16, the second shaft 18, and the output shaft 22 are coaxial, and do not impede mutual rotational movement.

  As a result, the third gear 19 rotates around the third shaft 20 and revolves around the output shaft 22 while meshing with the first gear 15 and the second gear 17. As the third gear 19 revolves, the output shaft 22 rotates to generate a driving force.

At this time, when the rotational speeds of the first gear 15 and the second gear 17 are ω1, ω2, and the first gear 15, the second gear 17, and the third gear 19 are z1, z2, and z3, the output shaft rotates. The number ω3 is as follows.
ω3 = (z1ω1 + z2ω2) / (2Z1 + 2Z3)
For example, even if z1 = z3 and z2 = z1 + 2z3 and the low speed limit of ω2 is 30 rpm, a speed of 1 rpm can be obtained by moving ω1 at 86 rpm in the opposite direction. In this case, as compared with the first embodiment, the distribution of the rotational speeds of the first gear 15 and the second gear 17 is not uniform. As a countermeasure, the non-uniformity is eliminated by using a reduction gear or speed increaser with an appropriate gear ratio before driving the gear.

  The load applied to the output shaft 22 is evenly distributed to the first ultrasonic motor and the second ultrasonic motor via the first gear 15 and the second gear 17. Therefore, the torque that can be generated by this transmission device is twice the torque of the ultrasonic motor alone.

  FIG. 3 shows an embodiment in which the transmission device for an ultrasonic motor using a differential gear according to the present invention is constituted by a spur gear. The ultrasonic motor is omitted to focus on the movement of the differential gear.

  The first gear 23 is a spur gear and is driven by a first ultrasonic motor. The axis is referred to as a first axis 24.

  The second gear 27 is a spur gear and meshes with the first gear 23. Driven by the second ultrasonic motor. The axis is referred to as a second axis 28.

  The second gear 27 can freely rotate around the second shaft 28. The second shaft 28 is integrated with the output shaft 32. The first shaft 24 and the output shaft 32 are coaxial and do not interfere with each other's movement.

  As a result, the second gear 27 rotates around the second shaft 28 and revolves around the output shaft 32 while meshing with the first gear 23. As the second gear 27 revolves, the output shaft 32 rotates to generate a driving force.

  For example, when the first gear 23 and the second gear 27 have the same number of teeth, when the first gear 23 and the second gear 27 rotate in the opposite directions at the same speed, the third gear 29 rotates at the same place and the output shaft 32 is rotated. Does not rotate. In this state, the rotational motion of the first ultrasonic motor is completely offset by the rotational motion of the second ultrasonic motor.

  For example, when the first gear 23 and the second gear 27 have the same number of teeth, when the first gear 23 and the second gear 27 rotate in the opposite directions and the first gear 23 rotates slightly faster, the second gear 27 Revolve in the same direction as the first gear 23 at half the difference in speed between the second gear 27 and the second gear 27, and the output shaft 32 also rotates in the same speed direction. For example, even if the low speed limit of the first ultrasonic motor and the second ultrasonic motor is 30 rpm, the rotation of (32-30) / 2 = 1 rpm is obtained by rotating one at 32 rpm and the other at 30 rpm. I can do it.

  For example, when the first gear 23 and the second gear 27 have the same number of teeth, and the first gear 23 and the second gear 27 rotate in the same direction at the same speed, the first gear 23 and the second gear 27 have the same speed direction. Revolving, the output shaft 32 also rotates in the same speed direction.

  For example, when the first gear 23 and the second gear 27 have the same number of teeth, the load applied to the output shaft 32 is halved through the first gear 23 and the second gear 27 and the first ultrasonic motor and the second ultrasonic wave. Distributed to the motor. Therefore, the torque that can be generated by this transmission device is twice the torque of the ultrasonic motor alone.

  In this embodiment, the second ultrasonic motor moves as the second gear 27 revolves. As a method of eliminating this inconvenience, a method of transmitting the driving force with a belt by fixing the second ultrasonic motor can be considered. In this state, the belt is replaced with the second gear 17 of the second embodiment, and the second gear 27 is replaced with the third gear 19 of the second embodiment. That is, replacing the gear with a belt is not an essential difference of the present invention.

  By using it for a manipulator that must use an ultrasonic motor because of its non-magnetic required specifications, it is possible to improve speed control and trajectory tracking while maintaining such non-magnetism. If used in an MRI-compatible master / slave manipulator that supports surgery in MRI, the movement of the operator can be reproduced more smoothly than before. Similarly, if it is used for a manipulator that performs puncture incision in MRI, a precise and smooth trajectory can be realized.

It is a figure explaining the Example by which the transmission apparatus of the ultrasonic motor by the differential gearing which concerns on this invention 2 was comprised by the bevel gear. The state before each component is assembled and the state after it is assembled are shown. In the assembly drawing, elements other than the main shaft are shown in a cut model. It is a figure explaining the Example by which the transmission device of the ultrasonic motor by the differential gearwheel which concerns on Claim 2 of this invention was comprised by the spur gear. The ultrasonic motor is omitted to explain the movement of the differential gear. It is a figure explaining the Example by which the transmission device of the ultrasonic motor by the differential gearing concerning this invention was comprised by the spur gear. The ultrasonic motor is omitted to explain the movement of the differential gear.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st ultrasonic motor stator 2 1st ultrasonic motor rotor 3 1st gear 4 1st axis 5 2nd ultrasonic motor stator 6 2nd ultrasonic motor rotor 7 2nd gear 8 2nd axis 9 3rd gear 10 3rd axis 11 Clasp 12 Output shaft 15 First gear 16 First shaft 17 Second gear 18 Second shaft 19 Third gear 20 Third shaft 22 Output shaft 23 First gear 24 First shaft 27 Second gear 28 Second shaft 32 Output shaft

Claims (2)

A first gear driven by a first ultrasonic motor;
A second gear driven by a second ultrasonic motor;
One or more third gears meshing with the first gear and the second gear;
A transmission device for an ultrasonic motor, characterized in that it has a differential gear which is integrated with the rotation shaft of the third gear and which has an output shaft driven by the revolution of the third gear. A first gear driven by a first ultrasonic motor;
One or more second gears driven by a second ultrasonic motor and meshing with the first gear;
A transmission device for an ultrasonic motor, comprising a differential gear which is integrated with a rotation shaft of a second gear and has an output shaft driven by revolution of the second gear.

Images