Steering unit and travelling movable body

Abstract

To inhibit impact added to a travelling movable body 100 from being transmitted to an output source of steering torque.SOLUTION: A steering unit SU includes: a piezoelectric motor PM that outputs steering torque for steering a wheel 20 and includes an output shaft OS; a rotary part 50 that rotates together with the wheel 20 with the steering torque; and an intermediate transmission mechanism 40 disposed between the output shaft OS and the rotary part 50 to transmit the steering torque to the rotary part 50.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a steering unit including a piezoelectric motor, and a traveling vehicle including the steering unit. [Background technology]

[0002] Patent Document 1 describes an electric power steering unit that uses an ultrasonic motor to assist the steering force of a steering shaft. This electric power steering unit changes the direction of the wheels via a steering shaft connected to a steering wheel. The steering force of the steering shaft is assisted by the ultrasonic motor via a clutch. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-353075 Summary of the Invention [Problem to be solved by the invention]

[0004] Steering units are used to steer each wheel of a traveling vehicle equipped with multiple wheels, such as an automated guided vehicle. For example, such a steering unit corresponds to each wheel and steers the traveling direction of the traveling vehicle. Furthermore, it is conceivable to adopt a piezoelectric motor as an output source of steering torque for steering each wheel. For example, a piezoelectric motor includes a rotor and a stator. In a stationary piezoelectric motor, the rotation of the rotor is restricted by a pressing force when one of the rotor and the stator is pressed against the other (i.e., a frictional force between the two).

[0005] As a result, in a steering unit using a piezoelectric motor, when no drive voltage is applied, steering can be suppressed and the traveling direction can be maintained. However, when an impact is applied to a traveling moving body, the impact may cause the rotor to separate from the stator and the rotor to rotate slightly. For example, when the traveling moving body descends a step or climbs up a step, an impact may be applied to the traveling moving body. Therefore, it is desirable to suppress the transmission of the impact applied to the traveling moving body to the piezoelectric motor. [Means for solving the problem]

[0006] A steering unit according to one aspect includes: a piezoelectric motor that outputs a steering torque for steering wheels and has an output shaft; a rotating portion that rotates together with the wheels due to the steering torque; and an intermediate transmission mechanism disposed between the output shaft and the rotating portion for transmitting the steering torque to the rotating portion.

[0007] In addition, a traveling vehicle according to another aspect is The steering unit; a wheel holder fixed to a rotating portion of the steering unit; a wheel that rotates together with the wheel holder in accordance with rotation of the rotating portion due to a steering torque; and a drive unit that drives the wheels. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic perspective view of a traveling vehicle. [Diagram 2] FIG. 2 is a schematic block diagram of a control system for a traveling vehicle. [Diagram 3] FIG. 1 is a schematic cross-sectional view of a piezoelectric motor. [Figure 4] FIG. 2 is a schematic perspective view of a steering unit. [Diagram 5] FIG. 2 is a schematic side view of a steering unit. [Figure 6] FIG. 2 is a schematic cross-sectional view of a steering unit. [Figure 7] FIG. 2 is a schematic perspective view of a first holder. [Figure 8] FIG. 4 is a schematic perspective view of a second holder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, exemplary embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of components described in the following embodiments can be arbitrarily set and can be changed according to the configuration or various conditions of the device or method to which the present invention is applied. In addition, unless otherwise specified, the scope of the present invention is not limited to the embodiments specifically described below.

[0010] In the following description, the side of the running vehicle 100 where the wheels 20 are located corresponds to the "lower side", and the opposite side corresponds to the "upper side". Also, the front side in the running direction of the running vehicle 100 (i.e., the forward direction side) corresponds to the "front", and the opposite side, the rear side (i.e., the backward direction side), corresponds to the "rear side". Furthermore, the rotation of a certain member and another member includes a mode in which the other member rotates in synchronization with the rotation of a certain member, and a mode in which the other member rotates due to a rotational force transmitted directly or indirectly from a certain member. EXAMPLES

[0011] [Mobile vehicle] The running vehicle 100 will be described with reference to Figures 1 and 2. Figure 1 is a schematic perspective view of the running vehicle 100 as seen from the front. Figure 2 is a schematic block diagram of a control system of the running vehicle 100.

[0012] As shown in Fig. 1, the running vehicle 100 includes a substantially rectangular parallelepiped main body 10 and wheels 20 suspended below the main body 10. Specifically, the running vehicle 100 in Fig. 1 includes a pair of front wheels and a pair of rear wheels. Therefore, the running vehicle 100 shown in Fig. 1 includes four wheels 20. However, for ease of explanation, reference symbols are given in Fig. 1 only to a right front wheel, which is one of the pair of front wheels, and a left rear wheel, which is one of the pair of rear wheels.

[0013] Moreover, all four wheels 20 have the same structure. Therefore, in the following description, one wheel 20 will be mainly described. Alternatively, the multiple wheels 20 may include wheels 20 with different shapes or sizes. Note that the traveling vehicle 100 only needs to have a front wheel and a rear wheel, and may have two, three, or five or more wheels 20. For example, the traveling vehicle 100 may have one front wheel and two rear wheels.

[0014] The main body 10 of the traveling mobile body 100 has a loading platform on which an article to be transported is mounted. Alternatively, in addition to or instead of the loading platform, the main body 10 may be provided with a device such as an agricultural robot, an exploration robot, an inspection robot, a robot arm, or a communication robot.

[0015] The traveling vehicle 100 also includes a steering unit SU that steers the wheels 20. A steering unit SU is provided corresponding to each wheel 20. Therefore, the traveling vehicle 100 shown in Fig. 1 includes four steering units SU. However, for ease of explanation, reference symbols are given in Fig. 1 only to the steering unit SU that steers the right front wheel and the steering unit SU that steers the left rear wheel.

[0016] All four steering units SU have the same structure. Therefore, in the following description, one steering unit SU will be mainly described. Alternatively, the multiple steering units SU may include steering units SU with different sizes, materials, etc.

[0017] The wheels 20 are held by wheel holders 30. An upper portion of the wheel holder 30 is fixed to a lower portion of the steering unit SU (specifically, a rotating portion 50 described later). The wheels 20 are connected to the corresponding steering unit SU by the wheel holders 30. The wheel holders 30 and the wheels 20 are connected to the steering unit SU so as to be rotatable in a horizontal plane perpendicular to the up-down direction in FIG. 1 and extending in the left-right direction (i.e., the XY plane in FIG. 4).

[0018] Each steering unit SU includes a piezoelectric motor PM, which is an example of a steering unit that steers the wheels 20. The piezoelectric motor PM is covered by a cover. The piezoelectric motor PM can steer the corresponding wheels 20 arbitrarily. That is, the wheels 20 can rotate at any rotation angle on a horizontal plane. For example, when traveling straight on a leveled ground, the piezoelectric motor PM is controlled so that the wheels 20 are positioned at the initial position shown in FIG. 1. When turning right, the steering torque applied to each wheel 20 is controlled so that each wheel 20 rotates rightward. Conversely, when turning left, the steering torque applied to each wheel 20 is controlled so that each wheel 20 rotates leftward. In the following description, the rotation of the wheels 20 on a horizontal plane is also referred to as "steering rotation."

[0019] The traveling vehicle 100 also includes a drive motor DM, which is an example of a drive unit that drives the wheels 20. The drive motor DM is provided corresponding to each wheel 20. Therefore, the traveling vehicle 100 shown in Fig. 1 includes four drive motors DM. However, for ease of explanation, reference symbols are given in Fig. 1 only to the drive motor DM that drives the right front wheel and the drive motor DM that drives the left rear wheel.

[0020] All four drive motors DM have the same structure. Therefore, in the following description, one drive motor DM will be mainly described. Alternatively, the multiple drive motors DM may include drive motors DM with different output torques or sizes. As an example, the drive motor DM is a DC motor capable of forward and reverse rotation. Alternatively, the drive unit may be a traveling wave type ultrasonic motor, etc.

[0021] The wheel holder 30 has a holder cover. This holder cover houses a transmission mechanism that transmits the drive torque from the drive motor DM to the wheels 20. As an example, the transmission mechanism is a gear train connected to a drive shaft that is the output shaft of the drive motor DM. This transmission mechanism can prevent an impact applied to the traveling mobile body 100 from being directly transmitted to the drive motor DM.

[0022] As an example, the transmission mechanism for transmitting the driving torque has a first spur gear and a second spur gear. This first spur gear is fixed to the drive shaft of the drive motor DM and meshes with a second spur gear fixed to the wheel shaft of the wheel 20. As a result, the driving torque from the drive motor DM is transmitted to the wheel 20 via the first and second spur gears and the drive shaft. Then, the wheel 20 to which the driving torque is transmitted rotates forward or backward, and the traveling mobile body 100 moves forward or backward. Note that the transmission mechanism may have other members such as a belt, a pulley, a bevel gear, and a worm gear instead of or in addition to the first and second spur gears.

[0023] Each drive motor DM can drive the corresponding wheel 20 in an arbitrary manner. That is, an arbitrary drive torque can be applied to each wheel 20. For example, when traveling straight on a level ground, the drive motor DM is controlled so that the wheels 20 rotate at the same rotation speed. When turning right, the drive torque applied to the left wheel 20 is controlled so that the left wheel 20 rotates more than the right wheel 20. Conversely, when turning left, the drive torque applied to the right wheel 20 is controlled so that the right wheel 20 rotates more than the left wheel 20.

[0024] The traveling vehicle 100 includes a detection unit 94 shown in FIG. 2, a control unit 95 as a computer, and a storage unit 96. The detection unit 94 includes a rotation speed detection sensor, a rotation number detection sensor, an angular velocity sensor, an acceleration sensor, a weight sensor, an obstacle sensor, a wheel speed sensor, a contact detection sensor, an inclination sensor, and a camera. As an example, the detection unit 94 detects an image of an obstacle such as a step approaching the traveling vehicle 100, a distance to the obstacle, and a traveling speed of the traveling vehicle 100. The detection unit 94 then transmits the acquired information and image to the control unit 95. Furthermore, the detection unit 94 may detect contact with an obstacle and transmit a contact detection signal to the control unit 95. The traveling vehicle 100 also has a power source (not shown) that supplies power to each electrical component.

[0025] As an example, the control unit 95 is a processor, and the storage unit 96 is a memory that stores a control program. The processor is, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit), and controls the entire device and also centrally controls various processes based on the program stored in the memory. The memory includes a RAM (Random Access Memory), which is a system work memory for the processor to operate, as well as a ROM (Read Only Memory) that stores the program and system software, and storage devices such as an HDD (Hard Disc Drive) and an SSD (Solid State Drive).

[0026] Alternatively, the control unit 95 can perform control according to a program stored in a portable recording medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), a CF (Compact Flash) card, or a USB (Universal Serial Bus) memory, or an external storage medium such as a server on the Internet. In the following, an example will be mainly described in which the CPU executes various processing operations such as calculations, controls, and determinations according to a control program stored in a ROM or HDD.

[0027] The control unit 95 controls the rotation speed of each wheel (i.e., the drive torque output by the drive motor DM) so that the wheels rotate at the required number of rotations. For example, when traveling straight on level ground, the control unit 95 controls each drive motor DM so that the rotation speeds of all the wheels 20 are the same. Note that, although one detection unit 94 is illustrated in FIG. 2, there may be multiple detection units 94. For example, the traveling mobile body 100 may have, as the multiple detection units 94, a rotation speed detection unit, a rotation number detection unit, a traveling speed detection unit, an acceleration detection unit, a weight detection unit, an obstacle detection unit, and the like.

[0028] Furthermore, the multiple detection units 94 may be configured as functional units that are logically realized as various functions in the control unit 95 that acquires information from the detection sensors. These functional units are realized as various functions by the control unit 95 executing various processes in accordance with the programs recorded in the storage unit 96.

[0029] As an example, the control unit 95 acquires the rotation state of the drive motor DM and the rotation angle of the piezoelectric motor PM from the detection unit 94. Then, the control unit 95 calculates the target rotation angle of the piezoelectric motor PM as a target angle for the steering rotation of the wheel 20 based on the rotation angle of the piezoelectric motor PM acquired by the detection unit 94. Furthermore, the control unit 95 controls the piezoelectric motor PM so as to reach the target rotation angle. Then, when the target rotation angle is reached, the control unit 95 stops the piezoelectric motor PM and maintains the traveling direction by the stationary torque. Alternatively, the control unit 95 may control the piezoelectric motor PM so as to reach the target rotation angle according to an operation command from an operation device. For example, this operation device is operated by an operator and is connected to the traveling vehicle 100 by wire or wirelessly.

[0030] [Piezoelectric motor] Next, the piezoelectric motor PM of the steering unit SU will be described with reference to Fig. 3. Fig. 3 is a schematic cross-sectional view of the piezoelectric motor PM. Fig. 3 shows a cross section along the longitudinal direction of the output shaft OS and passing through the rotation axis of the output shaft OS.

[0031] The piezoelectric motor PM includes a substantially plate-shaped base 141 and a case 134 that is screwed to the base 141. The piezoelectric motor PM also includes an output shaft OS that penetrates the base 141 and the case 134 and protrudes from the base 141 and the case 134. The piezoelectric motor PM also includes a connector having a plurality of conductive pins for connecting to the outside. This connector is attached to the side surface of the base 141.

[0032] The piezoelectric motor PM has a configuration that is approximately rotationally symmetrical about the rotation axis of the output shaft OS. The piezoelectric motor PM has a stator 111 and a rotor 121 that is a driven body. The stator 111 is fixed to a base 141, and the rotor 121 faces the stator 111. The stator 111 and the rotor 121 are stored in a substantially cylindrical space in a case 134.

[0033] A hole through which the output shaft OS passes is formed in the base 141, and a bearing 137 is disposed in this hole. Alternatively, a bush may be attached by press fitting instead of the bearing 137. Furthermore, a hole through which the output shaft OS passes is also formed in the case 134, and a bearing 138 is attached at a position corresponding to this hole. That is, the output shaft OS passes through each of the bearings 137 and 138. Furthermore, the output shaft OS passes through the centers of the approximately ring-shaped stator 111 and rotor 121, respectively. Therefore, the stator 111 and the rotor 121 are coaxial with the rotation axis of the output shaft OS.

[0034] The piezoelectric motor PM also includes a piezoelectric element 112, such as a piezo element, for driving a driven body, and a flexible printed circuit board 115 electrically connected to the piezoelectric element 112. Specifically, a step portion 142 is formed in the base 141, and the printed circuit board 115 is placed on this step portion 142. Also, on the inside of the step portion 142, a substantially ring-shaped annular groove portion 144 is formed so as to receive the edge portion of the elastic body 113 on the output shaft OS side.

[0035] The stator 111 has a piezoelectric element 112, an elastic body 113, and a sliding material 114. The piezoelectric element 112 and the sliding material 114 are attached to the elastic body 113. The stator 111 is fixed to a base 141 by a plurality of stator screws 116. Specifically, the edge of the elastic body 113 on the output shaft OS side has a screw hole. The base 141 has a screw hole corresponding to the screw hole of the elastic body 113. The stator 111 is fixed to the base 141 by the stator screws 116 being screwed into both screw holes. The rotor 121 has an annular member 120. The annular member 120 has a base portion 122 that abuts against the sliding material 114, and a disc spring portion 123 that is formed integrally with the base portion 122.

[0036] The piezoelectric element 112, the elastic body 113, and the sliding material 114 are arranged in this order from the base 141 toward the rotor 121. As an example, the sliding material 114 can be formed of a cross-linked fluororesin containing reinforcing fibers. This allows the reinforcing fibers to suppress deformation of the sliding material 114 when the base portion 122 of the rotor 121 is pressed against the sliding material 114. Furthermore, the wear resistance can be improved, thereby extending the life of the sliding material 114 and, ultimately, the life of the piezoelectric motor PM.

[0037] Elastic body 113 can be made of metal such as iron, steel, duralumin, copper alloy, titanium alloy, etc. Elastic body 113 has a plurality of comb teeth. Rectangular grooves extending radially from the center of elastic body 113 to the outer periphery of elastic body 113 are formed between the comb teeth.

[0038] When a drive voltage is applied to the piezoelectric motor PM, the expansion and contraction of the piezoelectric element 112 causes a flexural vibration in the elastic body 113, generating a traveling wave in the circumferential direction. At each apex of this traveling wave, the rotor 121 contacts the elastic body 113 via the sliding material 114. Each apex moves in an elliptical motion, and the locus of the elliptical motion is in the opposite direction to the traveling direction of the traveling wave. Therefore, the rotor 121 rotates in the opposite direction to the traveling wave. As a result, the output shaft OS rotates in the same direction as the rotor 121 as the rotor 121 rotates.

[0039] The rotor 121 has a stabilizer 125 fixed to the output shaft OS as an example of a fixed portion to which the disc spring portion 123 of the annular member 120 is fixed. A hole is formed in the center of the annular member 120, and the annular member 120 and the stabilizer 125 are separate bodies. The rotor 121 is fixed to a flange 136 of the output shaft OS via a plurality of first rotor screws 124, the stabilizer 125, and a plurality of second rotor screws 126. An inner edge portion 127 located on the output shaft OS side of the disc spring portion 123 of the annular member 120 has a screw hole. Furthermore, an outer edge portion of the stabilizer 125 has a screw hole corresponding to the screw hole. The first rotor screw 124 is screwed into both screw holes, thereby fixing the disc spring portion 123 to the stabilizer 125.

[0040] The disc spring portion 123 functions as a spring for biasing the rotor 121 against the stator 111. This causes the base portion 122 to be pressed against the sliding material 114 of the stator 111. That is, the disc spring portion 123 biases the base portion 122 against the stator 111, thereby causing the rotor 121 to be in close contact with the sliding material 114. The disc spring portion 123 functions as a spring, thereby making it possible to reduce the size of the piezoelectric motor PM.

[0041] Moreover, the disc spring portion 123 is provided between the base portion 122 and the stabilizer 125 in the radial direction of the piezoelectric motor PM. In other words, the stabilizer 125 is fixed to the output shaft OS at a position closer to the output shaft OS than the disc spring portion 123. Specifically, corresponding screw holes are formed in the inner edge portion of the stabilizer 125 and in the flange 136 of the output shaft OS. The second rotor screw 126 is screwed into both the screw holes, thereby fixing the stabilizer 125 to the flange 136.

[0042] As an example, the stabilizer 125 can be made of a 5000 series aluminum alloy (e.g., A5052). This can suppress the amount of deformation of the stabilizer 125 when the case 134 is attached to the base 141. Therefore, the pressing force (i.e., the frictional force between the rotor 121 and the stator 111) when the rotor 121 is pressed against the stator 111 can be made stronger, and the torque of the piezoelectric motor PM can be increased. Furthermore, the variation in the pressing force between the rotor 121 and the stator 111 can be suppressed. That is, when the case 134 is attached, the stabilizer 125 is pressed against the base 141. This can suppress the variation in the pressing force caused by the large deformation of the stabilizer 125 when the rotor 121 is pressed against the stator 111. Note that, as an example, the annular member 120 can be made of a 7000 series aluminum alloy (e.g., A7075).

[0043] The stabilizer 125 can shorten the distance from the inner edge 127 of the disc spring portion 123 to the outer edge 128 of the disc spring portion 123. The stabilizer 125 absorbs vibrations, thereby further suppressing vibrations of the disc spring portion 123. For this purpose, the stabilizer 125 has an annular groove 129 centered on the rotation axis of the output shaft OS. The annular groove 129 has a substantially U-shaped cross section, and the bottom of the annular groove 129 is thinner than other portions of the stabilizer 125. Two or more annular grooves 129 may be formed in the stabilizer 125.

[0044] A spacer may be disposed between the bearing 138 and the stabilizer 125. This makes it possible to adjust the pressing force with which the rotor 121 is pressed against the stator 111 when the case 134 is attached to the base 141. Furthermore, instead of or in addition to this spacer, a spring (e.g., a disc spring) may be disposed between the bearing 138 and the stabilizer 125. This makes it possible to increase the pressing force with which the rotor 121 is pressed against the stator 111, thereby increasing the torque of the piezoelectric motor PM. Specifically, the rotor 121 can be pressed against the stator 111 by disposing a convex disc spring facing the stabilizer 125.

[0045] The piezoelectric motor PM may be made of a non-magnetic material. As an example of the non-magnetic material, the elastic body 113 is made of phosphor bronze, and the output shaft OS, the second rotor screw 126, the first rotor screw 124, and the stator screw 116 are made of brass. The case 134, the base 141, the disc spring portion 123, and the stabilizer 125 are made of aluminum. The stabilizer 125 and the annular member 120 may be integrally formed.

[0046] [Embodiment] Next, the steering unit SU will be described with reference to Fig. 4 to Fig. 8. Fig. 4 is a schematic perspective view of the steering unit SU. For convenience of explanation, the cover of the steering unit SU is omitted in Fig. 4. Fig. 5 is a schematic side view of the steering unit SU. For convenience of explanation, the first support member 83, the first support stay 84, and the second support member 88 are omitted in Fig. 5.

[0047] Fig. 6 is a schematic cross-sectional view of the steering unit SU. Fig. 6 shows a cross section along the vertical direction of the steering unit SU, passing through the rotation axis of the output shaft OS. Fig. 7 is a schematic perspective view of the first holder 60, showing the first holder 60 as seen from above. Fig. 8 is a schematic perspective view of the second holder 70, showing the second holder 70 as seen from above.

[0048] As described above, the traveling vehicle 100 includes the steering unit SU and the wheel holder 30 fixed to the rotating part 50 of the steering unit SU. The traveling vehicle 100 also includes the wheels 20 that rotate together with the wheel holder 30 as the rotating part 50 rotates due to the steering torque. The traveling vehicle 100 also includes a drive motor DM as an example of a drive part that drives the wheels 20. The steering unit SU also includes a piezoelectric motor PM. This piezoelectric motor PM outputs a steering torque for steering the wheels 20 and has an output shaft OS. The steering unit SU also includes a rotating part 50, which rotates together with the wheels 20 due to the steering torque.

[0049] In such a traveling vehicle 100, when the wheels 20 are not steered, the rotor 121 of the piezoelectric motor PM is stationary. For example, when traveling straight on level ground, the wheels 20 are located in the initial position shown in Fig. 1. The rotor 121 of the piezoelectric motor PM is stationary, and the turning rotation of the wheels 20 is restricted by the stationary torque of the piezoelectric motor PM. In this manner, when the turning rotation is restricted, it is desirable to suppress the transmission of an impact applied to the traveling vehicle 100 to the piezoelectric motor PM.

[0050] For this reason, the steering unit SU is equipped with an intermediate transmission mechanism 40 shown in Fig. 4. This intermediate transmission mechanism 40 is disposed between the output shaft OS of the piezoelectric motor PM and the rotating part 50, and transmits the turning torque to the rotating part 50. In other words, the intermediate transmission mechanism 40 is disposed midway along the turning torque transmission path from the output shaft OS to the rotating part 50.

[0051] For example, the intermediate transmission mechanism 40 has an intermediate gear 41 positioned between the output shaft OS and the rotating part 50. By providing the intermediate transmission mechanism 40, it is possible to suppress the impact applied to the traveling vehicle body 100 from being transmitted to the piezoelectric motor PM as the output source of the steering torque. In particular, when the traveling vehicle body 100 driven by the drive motor DM is traveling, the impact transmitted to the rotor 121 of the piezoelectric motor PM can be reduced. Therefore, it is possible to suppress the rotor 121 at rest from moving away from the stator 111 and rotating slightly.

[0052] Also, in the steering unit SU, the rotating part 50 has a first gear 51. And the intermediate transmission mechanism 40 has a second gear 42 that rotates together with the intermediate gear 41. This second gear 42 meshes with the first gear 51. Further, the intermediate gear 41 meshes with an output gear OS1 positioned at the tip of the output shaft OS. Also, the steering unit SU includes a first holder 60 that holds the rotating part 50. Further, the steering unit SU includes a second holder 70 that is separate from the first holder 60 and holds the piezoelectric motor PM.

[0053] The intermediate gear 41 and the second gear 42 are separate from each other. Alternatively, the second gear 42 may be integrally formed with the intermediate gear 41. Note that the intermediate transmission mechanism 40 may have, instead of or in addition to the intermediate gear 41 and the second gear 42, a belt, a pulley, gears (for example, bevel gears, spur gears, helical gears, planetary gears, and sun gears, etc.), or a worm gear, etc.

[0054] The tip of the output shaft OS is provided with a D-cut. And the output gear OS1 fits with the tip of the output shaft OS. Alternatively, the output gear OS1 may be attached to the tip of the output shaft OS by other methods such as screwing. Also, the output gear OS1 may be formed at the tip of the output shaft OS. Alternatively, a key groove may be formed at the tip of the output shaft OS.

[0055] The steering unit SU also includes a first pressing portion 80 that comes into contact with the rotating portion 50. When the rotating portion 50 is displaced in a direction parallel to a first axis that is the rotation axis of the rotating portion 50 (i.e., the Z direction in FIG. 4), the first pressing portion 80 comes into contact with the rotating portion 50. Specifically, the first pressing portion 80 has a first shaft 81 that is located on the first axis. The first shaft 81 comes into contact with an upper end surface of the rotating member 52 of the rotating portion 50, or is slightly separated from the upper end surface. When an impact is applied to the traveling vehicle 100 and the rotating member 52 of the rotating portion 50 is displaced upward in the Z direction, the first shaft 81 comes into contact with the rotating member 52.

[0056] Moreover, the first shaft 81 is rotatably supported by a substantially rectangular first support member 83 via a first bearing 82. Furthermore, the first support member 83 is fixed to the first holder 60 by a plurality of (for example, four) first support stays 84. However, in FIG. 4, only one first support stay 84 is given a reference symbol. Furthermore, the outer shape of the first support member 83 may be another polygonal shape such as a triangle, a circle, an ellipse, or any other arbitrary shape. Furthermore, the number of first support stays 84 may be one to three, or five or more.

[0057] The first pressing portion 80 can prevent or reduce the displacement of the rotating member 52 and the first gear 51 when the rotating member 52 of the rotating portion 50 is displaced upward in the Z direction. In addition, since the first pressing portion 80 receives the impact, the impact can be prevented from being transmitted to the intermediate transmission mechanism 40 and the piezoelectric motor PM. Furthermore, the rattling and wobbling of the rotating member 52 within the XY plane in FIG. 4 can be suppressed. The first shaft 81 in contact with the rotating member 52 rotates together with the rotating member 52. Therefore, the first shaft 81 is prevented from being a load on the rotation of the rotating member 52. The first pressing portion 80 may have a member having another three-dimensional shape, such as a cylinder, a sphere, or a truncated cone, instead of the first shaft 81.

[0058] The steering unit SU also includes a second pressing portion 85 that comes into contact with the output shaft OS. When the output shaft OS is displaced in a direction parallel to a second axis that is the rotation axis of the output shaft OS (i.e., the X direction in FIG. 4), the second pressing portion 85 comes into contact with the output shaft OS. Specifically, the second pressing portion 85 has a second shaft 86 that is located on the second axis. The second shaft 86 comes into contact with a side end face of the output shaft OS or is slightly separated from the side end face. When an impact is applied to the traveling vehicle 100 and the output shaft OS is displaced laterally in the X direction, the second shaft 86 comes into contact with the output shaft OS.

[0059] Moreover, the second shaft 86 is rotatably supported by a second support member 88 having a substantially U-shaped cross section via a second bearing 87. Furthermore, the second support member 88 is fixed to the second holder 70 by a plurality of (for example, four) screws. Note that the second support member 88 may have the same outer shape as the first support member 83. In this case, the second support member 88 is fixed to the second holder 70 by a support stay similar to the first support stay 84.

[0060] The second pressing portion 85 can prevent or reduce the displacement of the output shaft OS and the rotor 121 of the piezoelectric motor PM when the output shaft OS is displaced laterally in the X direction. In addition, the second pressing portion 85 receives the impact, so that the impact can be prevented from being transmitted to the piezoelectric motor PM. Furthermore, the rattling and wobbling of the output shaft OS within the YZ plane in FIG. 4 can be suppressed. The second shaft 86, which is in contact with the output shaft OS, rotates together with the output shaft OS. Therefore, the second shaft 86 is prevented from being a load on the rotation of the output shaft OS. The second pressing portion 85 may have a member having another three-dimensional shape, such as a cylinder, a sphere, or a truncated cone, instead of the second shaft 86.

[0061] As shown in FIG. 6, the rotating part 50 has a rotating member 52 having a substantially cylindrical shape. This rotating member 52 penetrates the first holder 60. A first gear 51 is screwed to the upper part of the rotating member 52 via a disk 53. The first gear 51 and the disk 53 are separate from the rotating member 52, but may be formed integrally with the rotating member 52. The wheel holder 30 is fixed to the lower part of the rotating member 52. For example, a screw hole is formed in the lower end surface of the lower part, and the wheel holder 30 is screwed to the lower end surface. Alternatively, the rotating member 52 and the wheel holder 30 may be formed integrally. In this case, the wheel holder 30 constitutes a part of the rotating part 50.

[0062] In this way, the wheel holder 30 is fixed to the steering unit SU via the rotating member 52. Then, the steering torque output by the piezoelectric motor PM is transmitted to the intermediate gear 41, the second gear 42, the first gear 51, the wheel holder 30, and the wheel shaft of the wheel 20. As a result, the wheel 20 is steered in response to the rotation of the piezoelectric motor PM.

[0063] Returning to FIG. 5, the disk 53 is formed with a knob 54. The steering unit SU has a pair of limit switches LS for detecting the knob 54. The limit switches LS are located on both sides of the disk 53, and are included in the detection unit 94 or send a detection signal to the detection unit 94. When the wheel 20 reaches a limit position, the knob 54 comes into contact with the limit switch LS. The limit switch LS detects that the wheel 20, which is being steered and rotated, has reached the limit position. Note that when the initial position of the wheel 20 is detected and used to initialize the position of the wheel 20, one of the pair of limit switches LS can be omitted.

[0064] The first holder 60 extends from the second holder 70 in a direction intersecting with the second holder 70. This direction is indicated by an arrow D1 in FIG. 6 and corresponds to the X direction in FIG. 4. As shown in FIG. 6, a thrust bearing 55 is disposed between the rotating part 50 and the first holder 60. Specifically, the thrust bearing 55 is disposed between the flange portion 52A of the rotating member 52 and a groove portion formed in the first holder 60. The thrust bearing 55 can receive an impact applied to the traveling mobile body 100 from below by dispersing it around the rotating member 52.

[0065] In addition, two bearings are arranged around the rotating member 52, that is, between the peripheral surface of the rotating member 52 and the first holder 60. These two bearings can prevent the rotating member 52 from tilting with respect to the rotation axis of the rotating member 52. Therefore, even if an impact is applied to the traveling mobile body 100, it is possible to prevent the meshing between the first gear 51 and the second gear 42 from shifting. Note that the upper one of the two bearings is separated from the disk 53, and a space is formed between them. In addition, the thrust bearing 55 located below the two bearings absorbs the impact, so damage to the two bearings can be prevented.

[0066] The second gear 42 is attached to a shaft member 43 that penetrates the intermediate gear 41. However, the second gear 42 may be formed integrally with the shaft member 43. Furthermore, two bearings 43A and 43B are arranged between the shaft member 43 and the intermediate gear 41 and the second holder 70. Therefore, the intermediate gear 41 and the second gear 42 are held by the second holder 70 via the two bearings 43A and 43B. The bearings 43A and 43B are arranged so as to press the intermediate gear 41 from the outside. Therefore, the intermediate gear 41 and the shaft member 43 are supported via the bearings 43A and 43B. This allows the bearings 43A and 43B to suppress positional deviation of the intermediate gear 41 and the shaft member 43. Furthermore, when an impact is applied to the traveling mobile body 100, the impact (i.e., a force pushing up from below) transmitted to the shaft member 43 via the gear 42 can be released to the second holder 70 via the bearings 43A and 43B. It should be noted that a bearing is also disposed between the output shaft OS and the second holder 70. Alternatively, each bearing of the steering unit SU may be a pressed-in bushing.

[0067] Furthermore, an encoder ENC is attached to the piezoelectric motor PM, which is included in the detection unit 94 or transmits a detection signal to the detection unit 94. The rotation angle of the piezoelectric motor PM is detected by the encoder ENC. The traveling vehicle 100 may be equipped with a potentiometer as an example of an angle sensor that detects the steering rotation angle of the wheels 20. The potentiometer is included in the detection unit 94 or transmits a detection signal to the detection unit 94.

[0068] Next, the first holder 60 and the second holder 70 will be described with reference to Fig. 7 and Fig. 8. In the following description, the direction in which the first holder 60 protrudes from the second holder 70 is the length direction of the first holder 60, which corresponds to the X direction in Fig. 7 and Fig. 8 (hereinafter, also simply referred to as the X direction). In addition, the direction perpendicular to the length direction of the first holder 60 and extending along the second holder 70 is the height direction of the first holder 60, which corresponds to the Z direction in Fig. 7 and Fig. 8 (hereinafter, also simply referred to as the Z direction). In addition, the direction perpendicular to the length direction and height direction of the first holder 60 is the width direction of the first holder 60, which corresponds to the Y direction in Fig. 7 and Fig. 8 (hereinafter, also simply referred to as the Y direction).

[0069] As an example, the first holder 60 and the second holder 70 are plate-shaped members, but may have other three-dimensional shapes such as a rectangular column, a cylinder, or a column. In addition, the first holder 60 protrudes in one direction from the second holder 70, but may protrude in both directions relative to the second holder 70. For example, the first holder 60 and the second holder 70 may be engaged in a T-shape or a cross shape. Similarly, the second holder 70 protrudes in one direction from the first holder 60, but may protrude in both directions relative to the first holder 60.

[0070] The first holder 60 shown in Fig. 7 extends in a direction intersecting with the second holder 70, and protrudes from the second holder 70 in the X direction shown in Fig. 7. The first holder 60 has a first engagement portion that engages with the second holder 70. Specifically, a recess 61 as an example of the first engagement portion is formed at an end of the first holder 60. The recess 61 has a pair of inner walls 62.

[0071] Also, the second holder 70 shown in FIG. 8 has a second engagement portion that engages with the recess 61. Specifically, a convex portion 71 is formed at an end of the second holder 70 as an example of a second engagement portion. This end of the second holder 70 is formed thinner than other portions, and the convex portion 71 is formed at the thin end. The convex portion 71 has an outer shape complementary to the inner shape of the recess 61. Therefore, the two engage with each other so that the convex portion 71 fits into the recess 61. The second holder 70 is formed with two wiring holes 74 through which wiring connected to the limit switch LS is inserted.

[0072] The protrusion 71 has a first contact portion that contacts the recess 61 to restrict displacement of the first holder 60 in the width direction (i.e., the Y direction) of the first holder 60. Specifically, the protrusion 71 has a pair of side walls 72 that contact a pair of inner walls 62 of the recess 61 as an example of the first contact portion.

[0073] Moreover, the convex portion 71 has a second contact portion that contacts the concave portion 61 in order to regulate the displacement of the first holder 60 in the height direction of the first holder 60 (i.e., the Z direction). Specifically, the convex portion 71 has a surface 73A that protrudes outward as an example of a second contact portion. This surface 73A contacts an upper surface 63A located above the concave portion 61. Furthermore, the convex portion 71 has a protruding portion 73B that protrudes outward as an example of a second contact portion. The upper surface of this protruding portion 73B contacts a lower surface 63B located below the concave portion 61.

[0074] The first holder 60 is screwed to the second holder 70, but there is a possibility that the first holder 60 may be displaced due to an impact. As an example, the displacement of the first holder 60 in the Y direction includes a displacement in a rotational direction in the XY plane, as shown by the solid arrow in Fig. 7. Also, as an example, the displacement of the first holder 60 in the Z direction includes a displacement in a rotational direction in the XZ plane and the YZ plane, as shown by the dashed arrow in Fig. 7.

[0075] When the first holder 60 is displaced in the rotational direction, the first gear 51 is displaced relative to the second gear 42. As a result, the stationary torque of the piezoelectric motor PM cannot suppress the steering rotation, that is, the position of the wheels 20 cannot be maintained. Therefore, the first contact portion regulates the displacement, preventing the meshing positions of the first gear 51 and the second gear 42 from being displaced. The second contact portion also regulates the displacement, preventing the first gear 51 and the second gear 42 from being separated.

[0076] The fixing screws for screwing the first holder 60 to the second holder 70 are inserted into the first holder 60 by penetrating the thin end of the second holder 70 from the outside of the second holder 70. The insertion direction of the fixing screws coincides with the direction in which the surface 73A protrudes and the direction in which the protruding portion 73B protrudes (i.e., the X direction). As another example of the first engaging portion, a convex portion may be formed at the end of the first holder 60. In this case, a concave portion having an inner shape complementary to the outer shape of the convex portion is formed at the end of the second holder 70 as another example of the second engaging portion.

[0077] The steering unit SU according to the first embodiment and the traveling vehicle 100 including the steering unit SU can prevent an impact applied to the traveling vehicle 100 from being transmitted to the piezoelectric motor PM as an output source of the steering torque. In other words, in a state in which the stationary torque of the piezoelectric motor PM is used to restrict the steering rotation of the wheels 20, an external force caused by an impact applied to the wheels 20 can be prevented from being directly transmitted to the output shaft OS. This can prevent the rotor 121 from being separated from the stator 111. Furthermore, damage to the piezoelectric motor PM can also be prevented.

[0078] Although the present invention has been described above with reference to each embodiment, the present invention is not limited to the above embodiment. Inventions modified without violating the present invention and inventions equivalent to the present invention are also included in the present invention. In addition, each embodiment and each modified form, and technical means included in each embodiment or each modified form can be appropriately combined without violating the present invention.

[0079] For example, the steering unit SU is applicable to all traveling mobile bodies 100 including vehicles and robots that move using the wheels 20. As an example, the steering unit SU can be applied to planetary exploration robots that travel on rough ground, unmanned mobile robots that travel in urban areas with many steps, electric wheelchairs, agricultural robots, inspection robots, and vehicles for traveling on rough ground. In addition, the autonomous traveling mobile body 100 can automatically deliver goods to a destination. In addition, the autonomous traveling mobile body 100 may travel together with a purchaser to support the transportation of goods. Furthermore, the autonomous traveling mobile body 100 may transport goods in buildings such as factories, warehouses, and offices.

[0080] Furthermore, the first holding portion 80 and the second holding portion 85 may be omitted. For example, in a traveling vehicle 100 that travels exclusively on level ground, at least one of the first holding portion 80 and the second holding portion 85 may be omitted. Furthermore, the members of the steering unit SU may be fixed to each other by a method other than screw fastening. For example, the second gear 42 may be fixed to the first gear 51 by adhesion or fusion. Furthermore, one steering unit SU may be used to steer a plurality of wheels 20. For example, a plurality of wheels 20 may be held in the wheel holder 30.

[0081] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes.

[0082] (Appendix 1) a piezoelectric motor that outputs a steering torque for steering wheels and has an output shaft; a rotating portion that rotates together with the wheels due to the steering torque; a steering unit including an intermediate transmission mechanism disposed between the output shaft and the rotating portion, the intermediate transmission mechanism transmitting the steering torque to the rotating portion.

[0083] (Appendix 2) 2. The steering unit described in claim 1, further comprising a first pressing portion that comes into contact with the rotating portion when the rotating portion is displaced in a direction parallel to a first axis that is a rotation axis of the rotating portion.

[0084] (Appendix 3) 3. The steering unit according to claim 1 or 2, further comprising a second pressing portion that comes into contact with the output shaft when the output shaft is displaced in a direction parallel to a second axis that is a rotation axis of the output shaft.

[0085] (Appendix 4) the steering unit includes a first holder that holds the rotating portion, and a second holder that is separate from the first holder and holds the piezoelectric motor, the first holder extends in a direction intersecting with the second holder and has a first engagement portion that engages with the second holder, the second holder has a second engagement portion that engages with the first engagement portion, 4. The steering unit according to claim 1, wherein the second engagement portion has a first abutment portion that abuts against the first engagement portion to regulate displacement of the first holder in a width direction of the first holder.

[0086] (Appendix 5) The steering unit described in Appendix 4, wherein the second engagement portion has a second abutment portion that abuts against the first engagement portion to regulate displacement of the first holder in the height direction of the first holder.

[0087] (Appendix 6) 6. The steering unit according to claim 4 or 5, wherein a thrust bearing is disposed between the rotating portion and the first holder.

[0088] (Appendix 7) 7. The steering unit according to any one of claims 1 to 6, wherein the intermediate transmission mechanism has an intermediate gear located between the output shaft and the rotating portion.

[0089] (Appendix 8) The rotating portion has a first gear, the intermediate transmission mechanism has a second gear that rotates together with the intermediate gear and meshes with the first gear, 8. The steering unit according to claim 7, wherein the intermediate gear meshes with an output gear located at an end of the output shaft.

[0090] (Appendix 9) A steering unit according to any one of claims 1 to 8; a wheel holder fixed to a rotating portion of the steering unit; a wheel that rotates together with the wheel holder in accordance with rotation of the rotating portion due to a steering torque; A driving unit that drives the wheels. [Explanation of symbols]

[0091] 20:Wheel 30: Wheel holder 40: Intermediate transmission mechanism 41: Intermediate gear 42: Second gear 50: Rotating part 51: First gear 55: Thrust bearing 60: First holder 61: Recess (first engagement portion) 70: Second holder 71: Protrusion (second engagement portion) 72: Side wall (first contact part) 73A: Surface (second contact part) 73B: Projection part (second contact part) 80: First holding part 85: Second holding part 100: Traveling vehicle OS: Output shaft OS1: Output gear PM: Piezoelectric motor SU: Steering unit

Claims

1. a piezoelectric motor that outputs a steering torque for steering wheels and has an output shaft; a rotating portion that rotates together with the wheels due to the steering torque; a steering unit including an intermediate transmission mechanism disposed between the output shaft and the rotating portion, the intermediate transmission mechanism transmitting the steering torque to the rotating portion.

2. 2. The steering unit according to claim 1, further comprising a first pressing portion that comes into contact with the rotating portion when the rotating portion is displaced in a direction parallel to a first axis that is a rotation axis of the rotating portion.

3. 2. The steering unit according to claim 1, further comprising a second pressing portion that comes into contact with the output shaft when the output shaft is displaced in a direction parallel to a second axis that is a rotation axis of the output shaft.

4. the steering unit includes a first holder that holds the rotating portion, and a second holder that is separate from the first holder and holds the piezoelectric motor, the first holder extends in a direction intersecting with the second holder and has a first engagement portion that engages with the second holder, the second holder has a second engagement portion that engages with the first engagement portion, The steering unit according to claim 1 , wherein the second engagement portion has a first abutment portion that abuts against the first engagement portion to restrict displacement of the first holder in a width direction of the first holder.

5. The steering unit according to claim 4 , wherein the second engagement portion has a second abutment portion that abuts against the first engagement portion to regulate displacement of the first holder in a height direction of the first holder.

6. The steering unit according to claim 4 , further comprising a thrust bearing disposed between the rotating portion and the first holder.

7. The steering unit according to claim 1 , wherein the intermediate transmission mechanism has an intermediate gear located between the output shaft and the rotating portion.

8. The rotating portion has a first gear, the intermediate transmission mechanism has a second gear that rotates together with the intermediate gear and meshes with the first gear, 8. The steering unit according to claim 7, wherein the intermediate gear meshes with an output gear located at an end of the output shaft.

9. A steering unit according to any one of claims 1 to 6; a wheel holder fixed to a rotating portion of the steering unit; a wheel that rotates together with the wheel holder in accordance with rotation of the rotating portion due to a steering torque; A driving unit that drives the wheels.

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