JP2012246954A - Rotational movement converting device - Google Patents

Abstract

A rotary motion conversion device in which a reduction ratio changes according to a load is provided.
A gripping device using a rotational motion conversion device includes a main shaft having a thread and a bearing that supports the main shaft, and a thread groove having a diameter larger than the diameter of the thread on a surface in contact with the main shaft. , And a bearing 150 having an outer ring that rotatably supports the inner ring. The bearing 150 is inclined at a predetermined inclination angle with respect to the axial direction of the main shaft 130, and moves linearly in the axial direction of the main shaft 130 when the main shaft 130 is rotated.
[Selection] Figure 1

Description

  The present invention relates to a rotary motion conversion device.

  Many machines include a rotary motion conversion device that converts a rotary motion of a motor or the like into a linear motion. In general, since a motor rotates at a high speed, it is necessary to use a reduction gear having an appropriate reduction ratio in order to effectively convert the rotational motion of the motor into linear motion. Patent Document 1 discloses a robot hand using a speed reducer with a constant reduction ratio.

JP 2008-178939 A

  When holding a thing with the robot hand of patent document 1, it is necessary to use the reduction gear of a large reduction ratio, so that required force is large. However, there is a trade-off relationship between force and speed in the reduction ratio, so if you try to handle a high load by increasing the reduction ratio, the finger is not loaded (for example, move your finger to the gripping target) There is a problem that the movement of the finger is slow even in the state of being).

  This invention is made | formed in view of such a problem, and it aims at providing the rotational motion converter which a reduction ratio changes according to load.

In order to achieve the above object, the rotational motion conversion device of the present invention comprises:
A spindle with a thread;
A bearing for supporting the main shaft, the inner ring having a thread groove having a diameter larger than the diameter of the thread on the surface in contact with the main shaft; and an outer ring for rotatably supporting the inner ring; With
The bearing is inclined at a predetermined inclination angle with respect to the axial direction of the main shaft, and linearly moves in the axial direction of the main shaft when the main shaft is rotated.
It is characterized by that.

  A bearing tilt mechanism for tilting the bearing may be provided so that the tilt angle can be changed.

A bearing support that rotatably supports the bearing about an intersecting direction intersecting the main shaft;
The bearing tilt mechanism includes an elastic body disposed between the bearing and the bearing support,
The bearing may rotate about the intersecting direction against the elastic force of the elastic body by an axial force applied to the bearing support or the main shaft.

  The elastic body may be a spring.

  According to the present invention, it is possible to provide a rotary motion conversion device in which a reduction ratio changes according to a load.

It is a figure for demonstrating the structure of the holding apparatus which concerns on embodiment of this invention, (A) is a side view of a holding apparatus, (B) is sectional drawing of a holding apparatus, (C) is a mobile body with which a holding apparatus is provided. It is the figure which looked at from the main axis direction. It is a figure for demonstrating the structure of the bearing with which the holding | grip apparatus shown in FIG. 1 is equipped, (A) is a figure for demonstrating the relationship between the thread groove of an inner ring | wheel and the thread of a main shaft, (B) is a perspective view of a bearing. FIG. 2C is a sectional view of the bearing. It is a figure for demonstrating operation | movement of the holding | gripping apparatus in the state in which the load is not applied to a moving body, (A) is sectional drawing of a holding | gripping apparatus, (B) is sectional drawing of a bearing. It is a figure for demonstrating operation | movement of the holding | gripping apparatus in the state in which the load was applied to the moving body, (A) is sectional drawing of a holding | gripping apparatus, (B) is sectional drawing of a bearing. It is a figure for demonstrating operation | movement of the holding | gripping apparatus in the state with a big load applied to the moving body, (A) is sectional drawing of a holding | gripping apparatus, (B) is sectional drawing of a bearing. It is a figure which shows a mode that the housing | casing part provided the stopper so that a bearing may not rotate more than fixed amount, (A) is sectional drawing of a bearing when a small load is applied to a main axis | shaft, (B) is a main axis | shaft. It is sectional drawing of a bearing when a big load is applied. It is a figure for demonstrating the crane apparatus using a rotational motion converter. It is a figure which shows the slant turning feed screw used in the Example. It is a figure which shows the robot gripper which mounted the slant turning feed screw. It is a figure which shows the experimental environment for verifying a suitable stopper position. It is a figure which shows the verification result of a suitable stopper position. It is a figure which shows the experimental environment for verifying the relationship between a load and a reduction gear ratio. It is a figure which shows the relationship between a load and a reduction ratio. It is a figure which shows the relationship between the electric current applied to a motor, and an output.

A gripping device using a rotary motion conversion device according to an embodiment of the present invention will be described with reference to the drawings.
The gripping device 100 is a device for gripping an object to be gripped with a strong force, and as shown in FIGS. 1A and 1B, a base 110, a motor 120, a main shaft 130, a moving body 140, and a bearing. 150.

  The base 110 is made of a heavy and sturdy material such as iron, and various parts such as a motor 120 and a main shaft 130 are installed. Further, the base 110 has a flat plate-shaped grip portion 111 having a plane directed in the axial direction of the main shaft 130 (hereinafter referred to as “main shaft direction”). The grip part 111 grips a grip target together with a moving body 140 described later.

  The motor 120 is composed of an electric motor having a rotating shaft 121. The rotation shaft 121 is fixed to one end of the main shaft 130 as shown in FIG.

  The main shaft 130 is composed of a metal rod-like body, and a helical thread is formed on the surface thereof. Both ends of the main shaft 130 are rotatably fixed to the base 110, and the main shaft 130 is freely rotated by the motor 120. The thread pitch of the main shaft 130 is the same as the pitch P of the thread groove of the inner ring 151 as shown in FIG. Further, the diameter r of the thread of the main shaft 130 is smaller than the diameter R1 of the thread groove of the inner ring 151 and larger than the diameter R2 of the thread of the inner ring 151.

  The moving body 140 is composed of a sturdy material such as iron, and as shown in FIG. 1B, is composed of a flat plate-shaped gripping portion 141 and a casing portion 142 having a cylindrical hole. . Note that the bottom surface and both side surfaces of the housing portion 142 are in contact with the base 110 through an oil film, as shown in FIG. Therefore, even when a large load is applied to the gripping portion 141, the moving body 140 can move forward while maintaining an upright posture.

  The bearing 150 is a ball bearing that supports the main shaft 130, and includes an inner ring 151, a spherical body 152, an outer ring 153, a horizontal shaft 154, and an elastic body 155. As shown in FIGS. 1B and 1C, the bearing 150 is installed inside a cylindrical hole of the housing 142.

  The inner ring 151 is formed of a cylindrical body, and a thread groove having a diameter slightly larger than the diameter of the thread of the main shaft 130 is formed on the inner peripheral surface thereof as shown in FIG. The inner ring 151 rotates together with the main shaft 130 by friction between the screw thread and the screw groove. As shown in FIG. 1B, the inner ring 151 is installed in a state slightly inclined from the main shaft direction. The central axis of the thread groove of the inner ring 151 is inclined at an inclination angle of, for example, about 1 ° to 30 ° with respect to the main axis direction in a state where no force is applied to the moving body 140 from the object.

  The spherical body 152 is a metal ball disposed between the inner ring 151 and the outer ring 153, and reduces the friction generated between the inner ring 151 and the outer ring 153 due to the rotation of the inner ring 151.

  The outer ring 153 is formed of a cylindrical body that is slightly larger than the inner ring 151, and supports the inner ring 151 via a spherical body 152 so as to be rotatable. As shown in FIG. 1C, the outer ring 153 is fixed to the moving body 140 via a horizontal shaft 154.

  The horizontal shaft 154 includes two shafts that support the bearing 150 and is installed in a direction orthogonal to the main shaft 130 (hereinafter referred to as “horizontal axis direction”). The bearing 150 can change an inclination angle with respect to the main shaft 130 by rotating around the horizontal shaft 154.

  The elastic body 155 is composed of a spring having a constant spring constant, and as shown in FIG. 2B, in a direction orthogonal to both the main axis direction and the horizontal axis direction (hereinafter referred to as “vertical axis direction”). is set up. Further, as shown in FIG. 2C, the elastic body 155 is installed at a position slightly deviated from the horizontal axis 154 in the main axis direction, and the bearing 150 is inclined by the elastic force.

  Next, the operation of the gripping device 100 having such a configuration will be described.

  As shown in FIG. 3A, the bearing 150 is in contact with the main shaft 130 in a slightly inclined state. For this reason, the thread of the main shaft 130 and the thread groove of the inner ring 151 are deeply engaged with each other at the portions (a) and (b) shown in FIG. In other words, it can be said that the main shaft 130 having a small diameter and the inner ring 151 having a large inner diameter are in contact with each other eccentrically as shown in FIG. 3B.

When the main shaft 130 is rotated, the inner ring 151 rotates together with the main shaft 130. However, as described above, the inner ring 151 is larger than the diameter of the main shaft 130. Does not rotate. As shown in (d) of FIG. 3B, the inner ring 151 rotates by 360 ° −θ ₁ when the main shaft 130 makes one rotation. This is the same as when the inner ring 151 is fixed so as not to rotate and the main shaft 130 is rotated by θ ₁ , so that the bearing 150 moves in the main shaft direction by this rotation angle difference θ _1. .

  When the main shaft 130 is rotated at a high speed, the moving body 140 moves linearly in the main shaft direction and finally comes into contact with the object to be grasped. Then, as shown in FIG. 4A, a load F as a reaction force from the object to be gripped acts on the moving body 140. The load F applied to the moving body 140 is transmitted to the bearing 150 through the horizontal shaft 154, and finally appears as a pressing force from the main shaft 130 as shown in FIG.

  With this pressing force, the bearing 150 rotates about the horizontal axis 154 against the elastic force of the elastic body 155. Then, the inclination angle of the bearing 150 becomes somewhat gentler than the initial inclination angle, as shown in FIG. Then, the screw thread and the screw groove engage with each other relatively shallowly. As a result, as shown in FIG. Get smaller.

When the difference in distance to the contact point is reduced, it can be seen that the difference in diameter between the main shaft 130 and the inner ring 151 is reduced as shown in FIG. As shown in (b), the rotation angle difference θ ₂ is smaller than the initial rotation angle difference θ ₁ . As a result, the moving speed of the moving body 140 becomes slower than the initial moving speed. Since the moving speed and the gripping force are in a trade-off relationship, the moving speed decreases and the moving body 140 exerts a large force (that is, the moving distance of the moving body 140 for one rotation of the motor 120 is short). Thus, the torque of the motor 120 is converted into a large gripping force).

  When the moving body 140 is further moved, as shown in FIG. 5A, the load received from the gripping object further increases. Then, the pressing force acting on the screw thread and the screw groove also increases, and finally, the inclination of the bearing 150 disappears as shown in FIG. Then, the screw thread and the screw groove are in a state of being completely meshed with each other by 360 °, and as shown in FIG. 5B, the distances from the central axis of the main shaft 130 and the inner ring 151 to the contact point are completely matched. As a result, the main shaft 130 and the inner ring 151 rotate in complete synchronization, and the moving body 140 does not move at all in the main shaft direction. As a result, the application of the gripping force to the gripping object is stopped.

  According to this embodiment, the reduction ratio can be changed according to the load applied to the moving body 140. That is, when no load is applied to the moving body 140, the moving body 140 can be moved quickly instead of weakening the gripping force of the moving body 140. Further, when a large load is applied to the moving body, the gripping force of the moving body 140 can be increased instead of reducing the moving speed of the moving body. Therefore, when the object is not gripped, the moving body 140 can be quickly moved to the gripping target, and when the gripping object starts to be gripped, the gripping target can be gripped with a strong force.

  Further, since the gripping device 100 does not use a dedicated actuator such as a hydraulic device or a magnet in order to change the reduction ratio, the device can be easily downsized.

  Further, when the gripping force becomes a certain level or more, the inclination angle of the bearing 150 becomes 0 °, and the movement of the moving body 140 is stopped, so that overload to the motor 120 can be suppressed.

  In addition, a stopper 143 for keeping the bearing 150 maintaining an inclination angle may be provided inside the housing 142. For example, as shown in FIG. 6A, the stopper 143 may be installed so as to protrude from the inner wall of the housing 142 at a position facing the elastic body 155 around the horizontal axis 154. Even if a load is applied to the moving body 140, as shown in FIG. 6B, since the inclination angle of the bearing 150 does not become 0 °, a strong gripping force can be continuously output.

  Further, the elastic body 155 is not limited to a spring, and may be an object made of a material exhibiting great elasticity such as rubber.

  In this embodiment, the inclination angle of the bearing 150 is changed using a load applied to the moving body 140 from the object. For example, the main shaft 130 is configured to be slightly movable in the main shaft direction. 6 (A) and 6 (B), the inclination angle of the bearing 150 may be changed by applying a load to the main shaft 130 in the main shaft direction.

  Further, the inclination angle of the bearing 150 is not limited to 1 to 30 °. The bearing 150 can be inclined at any angle larger than 0 ° and smaller than 90 ° with respect to the main axis direction.

  In this embodiment, the horizontal shaft 154 is installed in a direction orthogonal to the main shaft 130 (horizontal axis direction). However, if the bearing 150 can be tilted, it can be installed in any direction that intersects the main shaft 130. The installation position of the elastic body 155 is not limited to the vertical axis direction, and can be installed in any direction that intersects the main shaft 130 and the horizontal axis 154.

  In the present embodiment, the rotational motion conversion device is used as a gripping device. For example, as shown in FIG. 7, a pulley 210 is provided at one end of the base 110, and further, one end of the wire 220 through the pulley 210 is connected. The crane may be configured to lift the object by being fixed to the moving body 140. The rising speed of the object can be changed according to the weight of the object.

  It was verified that the rotational motion can be converted into a linear motion by the rotational motion conversion device of the present invention (hereinafter referred to as “obliquely turning feed screw”).

  The manufactured oblique turning feed screw is shown in FIG. The total mass is 13.8 g. The female screw uses a M4 coarse thread, and the pitch is 0.7 mm. The male thread also uses an M4 coarse mesh, but it is made slightly thinner by adjusting the die and molding, and the diameter measured at the tip of the crest is 3.6 mm. The outer ring has a small diameter of 14 mm. The spring constant of the spring is 1.8 N / m. FIG. 9 shows a robot gripper mounted with this oblique turning feed screw. The total mass is 184g. Gripping can be performed by moving the pinch mouth in the direction of (a). A brushless motor was used as the motor. The torque constant of the motor is 2.7 mNm / A and the mass is 13 g.

  We verified how the output force changes depending on the position of the stopper. The position of the stopper was adjusted by inserting a washer with a thickness of 0.05 mm. When the number of washers is increased, the length of the stopper shown in FIG. 6 is shortened. The force output when a constant current of 1.5 A was passed through the motor and the number of washers was changed was measured using a force sensor as shown in FIG. The experimental results are shown in FIG. From this experimental result, it can be seen that the position of the stopper is most appropriate when the number of washers is two.

  Next, the proposed mechanism was verified to change the reduction ratio according to the load. A string was attached to the output as shown in FIG. 12, and a load was applied by a weight. In order to obtain the reduction ratio, the rotational speed of the motor and the output speed were measured. The number of rotations of the motor was measured using a hall sensor, and the output speed was obtained by passing the string through a pulley as shown in FIG. 12 and measuring the rotation of the pulley with an encoder. The experimental results are shown in FIG. It can be seen that the reduction ratio Rr increases from 20 to 45 up to 2.0 kg in contact with the stopper and is substantially constant thereafter. The reduction ratio Rr is a value obtained by the following equation (1) when the male screw is considered as a cylinder with a radius r and the female screw is assumed as a cylinder with a radius R.

  Rr = R / (R−r) (Formula 1)

  Next, it was verified that the output force changes according to the current flowing through the motor. FIG. 14 shows the force when a current is supplied to the motor from 1.0 A to 2.0 A every 0.25 A. It can be seen that the force changes according to the current and becomes 134N at 2.0A.

  It can be used in many devices equipped with a mechanism for converting rotational motion into linear motion, including industrial robots.

DESCRIPTION OF SYMBOLS 100 Holding device 110 Base body 111 Holding part 120 Motor 121 Rotating shaft 130 Main shaft 140 Moving body 141 Holding part 142 Case part 143 Stopper 150 Bearing 151 Inner ring 152 Sphere 153 Outer ring 154 Horizontal axis 155 Elastic body 210 Pulley 220 Wire

Claims (4)

A spindle with a thread;
A bearing for supporting the main shaft, the inner ring having a thread groove having a diameter larger than the diameter of the thread on the surface in contact with the main shaft; and an outer ring for rotatably supporting the inner ring; With
The bearing is inclined at a predetermined inclination angle with respect to the axial direction of the main shaft, and linearly moves in the axial direction of the main shaft when the main shaft is rotated.
A rotary motion conversion device characterized by that. A bearing tilt mechanism for tilting the bearing so that the tilt angle can be changed,
The rotary motion conversion device according to claim 1. A bearing support that rotatably supports the bearing about an intersecting direction intersecting the main shaft;
The bearing tilt mechanism includes an elastic body disposed between the bearing and the bearing support,
The bearing rotates about the intersecting direction against the elastic force of the elastic body by an axial force applied to the bearing support or the main shaft.
The rotary motion conversion device according to claim 2. The elastic body is a spring;
The rotational motion conversion device according to claim 3.