Active Caster

Abstract

To provide an active caster that suppresses the deterioration of drive performance. [Solution] The active caster 10 according to this disclosure comprises a wheel 5, a first rotation transmission mechanism, and a second rotation transmission mechanism. The rotational force of the motor is transmitted via the first rotation transmission mechanism to the rotation of the wheel 5 around a pivot axis T along the vertical axis, and the rotational force of the motor is transmitted via the first and second rotation transmission mechanisms to the rotation of the wheel 5 around an axle 4. If the offset of the axle 4 from the pivot axis T in the horizontal direction perpendicular to the axle 4 is s>0, the reduction ratio of the second rotation transmission mechanism is G, and the radius of the wheel 5 is r, then r / G>s holds.

Description

[Technical Field]

[0001] This disclosure relates to an active caster. [Background technology]

[0002] Patent Document 1 discloses a technology for suppressing lateral slippage of a self-propelled robot. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-038433 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] If the friction generated when turning the tires while stationary is greater than the friction generated when the tires are rolling, the turning torque of the active caster may be insufficient, potentially reducing the driving performance of the active caster.

[0005] This disclosure is made in view of the above background and aims to provide an active caster that suppresses the deterioration of driving performance. [Means for solving the problem]

[0006] The active caster according to this disclosure comprises a wheel, a first rotation transmission mechanism, and a second rotation transmission mechanism, wherein the rotational force of a motor is transmitted via the first rotation transmission mechanism to the rotation of the wheel around a pivot axis along a vertical axis, and the rotational force of the motor is transmitted via the first and second rotation transmission mechanisms to the rotation of the wheel around an axle, and if the offset of the axle from the pivot axis in a horizontal direction perpendicular to the axle is s>0, the reduction ratio of the second rotation transmission mechanism is G, and the radius of the wheel is r, then r / G>s holds. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide an active caster that suppresses a decrease in driving performance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the operation of the active caster in the comparative example. [Figure 2] This diagram illustrates the challenges of the active caster in the comparative example. [Figure 3] This is a perspective view illustrating the configuration of an active caster according to Embodiment 1. [Figure 4] This is a diagram illustrating the drive force transmission path of the active caster according to Embodiment 1. [Figure 5] This diagram shows an active caster according to Embodiment 1, illustrated with graphic symbols. [Figure 6] This is a diagram illustrating the speed and thrust direction of the active caster according to Embodiment 1. [Modes for carrying out the invention]

[0009] Reference example Figure 1 is a diagram illustrating an example of the operation of an active caster according to a reference example. The active caster comprises a wheel 5 and a pivot axis T along a vertical axis. The wheel 5 is pivotally supported so as to be able to rotate around the pivot axis T which extends in the vertical direction. The axle of the wheel 5 is positioned horizontally offset from the pivot axis T, perpendicular to the axial direction of the axle. In other words, when viewed from above the wheel 5, the pivot axis T is located at a different position from the point of contact of the wheel 5 with the ground. The active caster may be provided on an omnidirectional vehicle.

[0010] The following diagram of FIG. 1 shows an example of the operation in which the active caster moves in the direction of the arrow. The wheel 5 rotates around the axle while rotating around the turning axis T. The horizontal axis in the upper diagram of FIG. 1 corresponds to the position of the wheel 5 in the lower diagram of FIG. 1. The curve C1 shows the rotational speed of the wheel 5 around the axle. The curve C2 shows the rotational speed of the wheel 5 around the turning axis T.

[0011] Referring to FIG. 2, the problems of the active caster according to the reference example will be described. The upper left diagram of FIG. 2 shows a schematic front view of the wheel 5. Usually, the wheel 5 contacts the floor surface at almost a single point. The lower left diagram of FIG. 2 shows a schematic top view of the wheel 5. The arc-shaped arrows in the upper left and lower left diagrams of FIG. 2 indicate the turning operation of the wheel 5. When the wheel 5 contacts the floor surface at a single point, the slippage of the wheel 5 during turning is small.

[0012] Referring to the upper right diagram of FIG. 2, when the rug 6 (e.g., carpet) formed of a flexible material is placed on the floor surface, the wheel 5 contacts the rug 6 in the region indicated by the dotted line. In this case, as shown in the lower right diagram of FIG. 2, a large slippage occurs in the wheel 5. The arc-shaped arrow inside the region surrounded by the dotted line represents the slippage of the wheel 5.

[0013] On the other hand, the resistance to the rotation of the wheel 5 around the axle is considered to be relatively small even when the wheel 5 travels on the rug 6. Since the active caster according to the comparative example does not consider the difference between the resistance during the turning of the wheel 5 and the resistance during the rotation of the wheel 5, there is room for improving the driving performance of the active caster.

[0014] Based on the above considerations, the inventor of the present application conceived the embodiments. Hereinafter, the embodiments will be described.

[0015] Embodiment 1 Figure 3 illustrates a perspective view of an active caster 10 according to Embodiment 1. The active caster 10 comprises motors M1 to M2, gearboxes 211 to 212, gearboxes 221 to 222, output shafts 31 to 32, axle 4, and wheel 5. Gearboxes 11 to 12 correspond to the first rotation transmission mechanism described above, and gearboxes 211 to 212 and gearboxes 221 to 222 correspond to the second rotation transmission mechanism described above.

[0016] Motors M1 and M2 may be motors with the same performance.

[0017] The gearbox 11 includes a timing belt that is stretched over the output shaft and driven pulley of the motor M1. The gearbox 12 includes a timing belt that is stretched over the output shaft and driven pulley of the motor M2. The driven pulleys of the gearbox 11 and the driven pulley of the gearbox 12 are supported so as to be rotatable around the pivot axis T. The reduction ratio of the gearbox 11 may be the same as the reduction ratio of the gearbox 12.

[0018] The gearbox 211 includes a pulley to which the driven pulley of the gearbox 11 is fixed at the top, a pulley fixed to the top of the output shaft 31, and a timing belt that is stretched over these pulleys. The gearbox 211 may further include an idler pulley.

[0019] The gearbox 212 comprises a pulley to which the driven pulley of the gearbox 12 is fixed at the top, a pulley fixed to the top of the output shaft 32, and a timing belt stretched over these pulleys. The gearbox 212 may further include an idler pulley. The reduction ratio of the gearbox 211 may be the same as the reduction ratio of the gearbox 212. Gearboxes 211 and 212 are also referred to as belt pulley gearboxes.

[0020] The gear reducer 221 comprises a bevel gear 2211 fixed to the lower part of the output shaft 31 and a bevel gear 2212 fixed to one side of the wheel 5. The bevel gears 2211 and 2212 mesh together. The gear reducer 222, like the gear reducer 221, comprises two bevel gears that mesh together, with one bevel gear fixed to the lower part of the output shaft 32 and the other bevel gear fixed to the other side of the wheel 5. The reduction ratio of the gear reducer 221 may be the same as that of the gear reducer 222. Gear reducers 221 and 222 are also called bevel gear reducers.

[0021] The wheel 5 is supported so as to be rotatable around the pivot axis T1. The support member that supports the wheel 5 or the axle 4 can also be considered as the pivot axis T.

[0022] For example, if motors M1 and M2 rotate in the same direction at the same speed, output shafts 31 and 32 also rotate in the same direction at the same speed. Since the direction in which output shaft 31 rotates the wheel 5 around the axle 4 is opposite to the direction in which output shaft 32 rotates the wheel 5 around the axle 4, the wheel 5 does not rotate around the axle 4, but rotates around the pivot axis T. On the other hand, if motors M1 and M2 rotate in opposite directions at the same speed, output shafts 31 and 32 rotate in opposite directions at the same speed, and the wheel 5 does not rotate around the pivot axis T, but rotates around the axle 4.

[0023] The power transmission path of the active caster 10 is shown in Figure 4. The sum of the rotational force of motor M1 transmitted via reduction gear 11 and the rotational force of motor M2 transmitted via reduction gear 12 is transmitted to the rotation of the wheel 5 around the pivot axis T. Then, the difference between the rotational force of motor M1 transmitted via reduction gears 11, 211, and 221 and the rotational force of motor M2 transmitted via reduction gears 12, 212, and 222 is transmitted to the rotation of the wheel 5 around the axle 4.

[0024] Figure 5 is a diagram illustrating the active caster 10 using graphic symbols. As already explained, the active caster 10 includes a pivot axis T and an axle 4. Let s (s>0) be the offset of the axle 4 from the pivot axis T in a direction perpendicular to the direction in which the axle 4 extends.

[0025] Referring again to Figure 4, let G1 be the reduction ratio of speed reducers 11 and 12, G21 be the reduction ratio of speed reducers 211 and 212, and G22 be the reduction ratio of speed reducers 221 and 222. The rotational speed transmission ratio from motors M1 and M2 to the slewing axis T is expressed as G1 ÷ s. Also, the rotational speed transmission ratio from motors M1 and M2 to axle 4 is expressed as G1 × G21 × G22 ÷ r, where r is the radius of wheel 5.

[0026] G21 × G22 corresponds to the above G. The rotational speed transmission ratio from motors M1 and M2 to axle 4 can also be expressed as G1 × G ÷ r.

[0027] The direction of the translational velocity of wheel 5 located in the area enclosed by the dashed line in the upper part of Figure 6 is different from the direction of the translational velocity of wheel 5 located in the area enclosed by the dotted line. The arrows, as in Figure 1, represent the direction of movement of wheel 5.

[0028] The lower left diagram of Figure 6 shows wheel 5 located in the area enclosed by the dashed line in the upper diagram of Figure 6. In the lower left diagram of Figure 6, the vertical direction corresponds to the front-to-back direction of wheel 5, and the left-to-right direction corresponds to the lateral direction of wheel 5. The curved arrows represent the rotation of wheel 5 around the axle 4. The translational velocity v of wheel 5. w and the thrust f generated in wheel 5 w It has an orientation along the longitudinal direction of wheel 5. Translational velocity v w and thrust f w In the opposite direction to the direction of, the rolling resistance f r This is happening.

[0029] The lower right diagram of Figure 6 shows wheel 5 located in the area enclosed by the dotted line in the upper diagram of Figure 6. The clockwise arrows represent the rotation of wheel 5 around its pivot axis T. The translational velocity v of wheel 5. s and the thrust f generated in wheel 5s is in the direction along the lateral direction of the wheel 5. In the direction opposite to the direction of rotation of the wheel 5 about the rotation axis T, a frictional force f d is generated.

[0030] If the rotational speeds of the motors M1 and M2 are ω m then v w and v s are expressed by the following equations.

Equation

Equation

[0031] Similarly, if the torques of the motors M1 and M2 are τ m then f w and f s are expressed by the following equations.

Equation

Equation

[0032] The values of G21, G22, s, and r of the active caster 10 are designed to satisfy the following equation.

Equation

[0033] If G21 × G22 = G, then Equation (5) can also be expressed as r / G > s. In the active caster 10, v w > v s , and, f w < f s holds. In the active caster 10, the thrust f s is relatively large, and it is possible to suppress the decrease in the driving performance of the wheel 5 due to the rotation of the wheel 5 about the rotation axis T, that is, the friction during the setting cut.

[0034] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its intent. [Explanation of Symbols]

[0035] 10 Active Caster 11, 12, 211, 212, 221, 222 reducer 2211, 2212 Bevel gear T pivot axis M1, M2 motors 31, 32 Output shafts 4 axles 5 wheels 6. Mat

Claims

1. It comprises a wheel, a first rotation transmission mechanism, and a second rotation transmission mechanism, The rotational force of the motor is transmitted via the first rotational transmission mechanism to the rotation of the wheel around a pivot axis along the vertical axis, and the rotational force of the motor is transmitted via the first rotational transmission mechanism and the second rotational transmission mechanism to the rotation of the wheel around the axle. Let s > 0 be the offset of the axle from the pivot axis in the horizontal direction perpendicular to the axle, let G be the reduction ratio of the second rotation transmission mechanism, and let r be the radius of the wheel. Then r / G > s holds true. Active caster.

2. It travels on a floor covered with carpets. The active caster according to claim 1.

3. The second rotational transmission mechanism comprises a belt pulley reducer and a bevel gear reducer, The reduction ratio of the second rotational transmission mechanism is expressed as the product of the reduction ratio of the belt pulley reducer and the reduction ratio of the bevel gear reducer. The active caster according to claim 1 or 2.

4. The translational speed of the wheel due to the wheel's rotation around the axle is v ｗ Let v be the translational speed of the wheel due to the wheel's rotation around the pivot axis. ｓ Therefore, v ｗ >v ｓ The following is true. The active caster according to claim 1 or 2.

5. Equipped on omnidirectional vehicles The active caster according to claim 1 or 2.

Images