Electric actuator system

Abstract

An electric actuator system comprises: a reference-side motor that generates rotational torque; a reference-side ball nut that is rotatably connected to a reference structure and includes a first conversion screw thread for generating translation along the direction of a translation axis by rotating in accordance with the torque generated by the reference-side motor; a movable-side motor that generates rotational torque; a movable-side ball nut that is rotatably connected to a movable structure and includes a second conversion screw thread for generating translation along the direction of the translation axis by rotating in accordance with the torque generated by the movable-side motor; and a ball screw shaft that extends from the reference-side ball nut toward the movable-side ball nut and includes a first connection screw thread which meshes with the first conversion screw thread and a second connection screw thread which meshes with the second conversion screw thread.

Description

Electric Actuator System

[0001] This disclosure relates to an electric actuator system.

[0002] Patent documents 1, 2, and 3 disclose drive mechanisms using mechanical components. Figure 1 of Patent Document 1 shows a structure in which two ball nuts are attached to one ball screw. Figure 4 of Patent Document 2 shows a structure in which a ball screw groove and a ball spline groove are provided on one shaft, and a ball nut and a ball spline unit are attached to it. Figure 1 of Patent Document 3 shows a structure in which a system including a ball screw and a nut and a system including a spline shaft and a sliding gear are arranged in parallel.

[0003] JP-A-60-155347, JP-A-4-254038, JP-A-4-66451

[0004] Aircraft are equipped with movable structures such as flaps, rudders, and ailerons. Hydraulic systems are used as the power source for these movable structures. The application of electric actuators as an alternative to these hydraulic systems has been considered for some time. Electric actuators are formed by mechanical components, such as those described in Patent Document 1, and electrical components such as motors.

[0005] However, mechanical and electrical components can each fail and lose their function. Therefore, the reliability of an electric actuator system composed of these components is evaluated based on the failure rate set for each component. When applying an electric actuator system to an aircraft, it must meet the required reliability.

[0006] This disclosure describes an electric actuator system that can enhance reliability.

[0007] One embodiment of the present disclosure is an electric actuator system for relatively changing the position of a second structure with respect to a first structure along a translation axis, comprising: a first motor for generating rotational torque; a first conversion unit rotatably connected to the first structure and including a first conversion screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the first motor; a second motor for generating rotational torque; a second conversion unit rotatably connected to the second structure and including a second conversion screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the second motor; and a first connecting unit extending from the first conversion unit toward the second conversion unit and including a first connecting screw thread that engages with the first conversion screw thread and a second connecting screw thread that engages with the second conversion screw thread.

[0008] This electric actuator system prevents the loss of all functions of the electric actuator system even if a failure occurs in the mechanical elements constituting the first and second converter units. Therefore, the reliability of the electric actuator system can be improved.

[0009] In the above-described electric actuator system, the relative position of the first transformer with respect to the first structure may be maintained even when the first transformer rotates, and the relative position of the second transformer with respect to the second structure may be maintained even when the second transformer rotates. This structure allows for the exertion of a force that changes the relative position of the second structure with respect to the first structure using a simple configuration.

[0010] In the above-described electric actuator system, the first motor, first converter, second motor, second converter, and first connector constitute the first actuator, and further comprises a second actuator connected to the first structure and the second structure respectively so as to be in parallel with the first actuator, wherein the second actuator may include a third motor that generates rotational torque, a third converter rotatably connected to the first structure and including a third converter screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the third motor, a fourth motor that generates rotational torque, a fourth converter rotatably connected to the second structure and including a fourth converter screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the fourth motor, and a second connector extending from the third converter toward the fourth converter and including a third connector screw thread that engages with the third converter screw thread and a fourth connector screw thread that engages with the fourth converter screw thread. With this configuration, even if either the first actuator or the second actuator loses its function, it is possible to prevent the loss of all functions in the electric actuator system. Therefore, reliability can be increased.

[0011] The above-described electric actuator system may further include a first sub-motor that generates torque to rotate the first conversion unit, and a second sub-motor that generates torque to rotate the second conversion unit. This configuration also enhances the reliability of the electric actuator system.

[0012] The above-described electric actuator system may further include a controller that generates a first control signal for a first motor and a second control signal for a second motor. The rotational speed of the first motor indicated by the first control signal may be the same as the rotational speed of the second motor indicated by the second control signal. With this configuration, it is possible to control the generation of a force that changes the relative position of the second structure with respect to the first structure.

[0013] The above-described electric actuator system further includes a controller that generates a first control signal and a third control signal for a first motor, the controller which generates the first control signal when the first converter can rotate relative to the first coupling part, and the controller which generates the third control signal when the first converter cannot rotate relative to the first coupling part, and the rotational speed of the first motor indicated by the first control signal may be the same as the rotational speed of the first motor indicated by the third control signal. With this operation, even if a failure occurs due to a mechanical element constituting the first converter part and the second converter part, it is possible to suppress the loss of all functions of the electric actuator system. Therefore, the reliability of the electric actuator system can be increased.

[0014] In the above-described electric actuator system, the first connecting portion may be a connecting screw shaft including a first connecting male screw portion formed by a first connecting screw thread and a second connecting male screw portion formed by a second connecting screw thread; the first conversion portion may be a first conversion nut including a through hole through which the connecting screw shaft is inserted, with a first conversion female screw portion formed by the first conversion screw thread on the inner circumferential surface of the through hole; and the second conversion portion may be a second conversion nut including a through hole through which the connecting screw shaft is inserted, with a second conversion female screw portion formed by the second conversion screw thread on the inner circumferential surface of the through hole. This configuration also makes it possible to suppress the loss of all functions of the electric actuator system. Therefore, the reliability of the electric actuator system can be improved.

[0015] In the above-described electric actuator system, the connecting screw shaft is a ball screw shaft, and the first conversion nut and the second conversion nut may each be a ball nut.

[0016] In the above-described electric actuator system, the first conversion part is a first conversion screw shaft including a first conversion male screw portion formed by a first conversion screw thread, the second conversion part is a second conversion screw shaft including a second conversion male screw portion formed by a second conversion screw thread, and the first connecting part may be a connecting nut including a through hole through which the first conversion screw shaft and the second conversion screw shaft are inserted, with a first connecting female screw portion formed by a first connecting screw thread and a second connecting female screw portion formed by a second connecting screw thread provided on the inner circumferential surface of the through hole. This configuration also makes it possible to suppress the loss of all functions of the electric actuator system. Therefore, the reliability of the electric actuator system can be increased.

[0017] In the above-described electric actuator system, the first connecting portion includes a connecting screw shaft including a connecting male thread formed by a first connecting screw thread, and a connecting nut including a through hole into which the connecting screw shaft is inserted, with a connecting female thread formed by a second connecting screw thread on the inner circumferential surface of the through hole; the first conversion portion is a first conversion nut including a through hole through which the connecting screw shaft is inserted, with a first conversion female thread formed by the first conversion screw thread on the inner circumferential surface of the through hole; and the second conversion portion may be a second conversion screw shaft including a second conversion male thread formed by the second conversion screw thread. This configuration also prevents the loss of all functions of the electric actuator system. Therefore, the reliability of the electric actuator system can be improved.

[0018] The electric actuator system of this disclosure can improve reliability.

[0019] Figure 1 is a diagram showing the physical configuration of the electric actuator system of the embodiment. Figure 2(a) is a perspective view showing the basic configuration of the actuator. Figure 2(b) is a graph illustrating the autonomous equilibrium of friction torque produced by the actuator shown in Figure 2(a). Figure 3(a) is a graph illustrating the autonomous equilibrium of friction torque produced under the condition that the friction torque of the second ball nut is extremely large compared to that of the first ball nut. Figure 3(b) is a graph illustrating the autonomous equilibrium of friction torque produced under the condition that the rotation angle of the first ball nut with respect to the reference frame is fixed. Figure 4 is a diagram showing the functional configuration of the electric actuator system of the embodiment. Figure 5(a) is a schematic diagram of an actuator system employing a force-addition type redundancy method. Figure 5(b) is a schematic diagram of an actuator system employing a speed-addition type redundancy method. Figure 5(c) is a schematic diagram of an actuator system employing the redundancy method of the embodiment. Figure 6 is a table comparing the fault tolerance performance of the actuator system employing a force-addition type redundancy method, the actuator system employing a speed-addition type redundancy method, and the electric actuator system of the embodiment. Figure 7 shows the physical configuration of the electric actuator system of the second embodiment. Figure 8 shows the physical configuration of the electric actuator system of the third embodiment. Figure 9 shows the physical configuration of the electric actuator system of the first modified example. Figure 10 shows the physical configuration of the electric actuator system of the second modified example.

[0020] Hereinafter, embodiments for implementing the electric actuator system of this disclosure will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted.

[0021] The electric actuator system 1 shown in Figure 1 moves the movable structure 102 relative to the reference structure 101. An example of the reference structure 101 is the wing structure of an aircraft. An example of the movable structure 102 is the control surface of an aircraft. In other words, the "reference" of the reference structure 101 means that it is the reference for the movement of the movable structure 102. The control surface moves relative to the wing structure so that the distance from the wing structure to the control surface changes.

[0022] First, the electric actuator system 1 of this embodiment, which has a mechanism utilizing the autonomous equilibrium of friction torque as shown in Figure 1, can be understood as the following first to third forms.

[0023] The first form is an electric actuator in which one or more motors are mounted on each of two nut mechanisms, and speed addition is performed by a ball screw.

[0024] The second embodiment is an electric actuator system in which two or more electric actuators defined in the first embodiment are arranged in parallel to connect a fixed structure and a movable structure.

[0025] The third embodiment is an electric actuator structure defined in the second embodiment, which is a control method that avoids loss of steering force by having the remaining electric actuator compensate when the force of one actuator is lost.

[0026] According to the first embodiment, an electric actuator system can be provided that does not lose control function even if a single seizure failure occurs. According to the second and third embodiments, an electric actuator system can be provided that does not lose control function even if control force is lost due to a single failure. Furthermore, according to the second and third embodiments, high reliability is provided by realizing a fully redundant configuration. For example, according to the second embodiment, 10 is required in the field of aircraft. －９ It is possible to achieve a failure rate of a certain level.

[0027] The following describes in detail the electric actuator system 1, which can take the first to third forms described above.

[0028] <Physical Configuration> The electric actuator system 1 includes multiple electric motors as its driving source. Thus, the electric actuator system 1 is a system that uses electricity as its driving source.

[0029] The electric actuator system 1 includes a first actuator 2F and a second actuator 2S. One end of the first actuator 2F is connected to a reference structure 101 (first structure). The other end of the first actuator 2F is connected to a movable structure 102 (second structure). The second actuator 2S is connected similarly. In other words, the electric actuator system 1 is arranged between the reference structure 101 and the movable structure 102 such that the first actuator 2F and the second actuator 2S are in parallel. This redundant configuration, consisting of two actuators connected in parallel, is called a force-adding type (see Figure 5(a)).

[0030] The first actuator 2F includes a ball screw shaft 3 (first connecting part, connecting screw shaft), a reference-side conversion mechanism 4, a reference-side motor 5 (first motor), a movable-side conversion mechanism 6, and a movable-side motor 7 (second motor). Furthermore, the reference-side conversion mechanism 4 includes a reference-side ball nut 41 (first conversion part, first conversion nut). The movable-side conversion mechanism 6 includes a movable-side ball nut 61 (second conversion part, second conversion nut).

[0031] Furthermore, the first actuator 2F may be configured with a mechanism that converts rotation to translation using components other than the ball screw shaft and ball nut. For example, a mechanism using an Acme screw may be adopted, or a mechanism using a roller screw may be adopted.

[0032] A connecting male thread portion R31 is provided on the outer circumferential surface of the ball screw shaft 3. The connecting male thread portion R31 may be formed by a plurality of threads that are continuous from the reference structure 101 side to the movable structure 102 side of the ball screw shaft 3. The connecting male thread portion R31 includes a reference-side connecting male thread portion R311 (first connecting male thread portion) and a movable-side connecting male thread portion R312 (second connecting male thread portion). The reference-side connecting male thread portion R311 is formed by a plurality of reference-side connecting threads R311a (first connecting threads) provided on the reference structure 101 side of the outer circumferential surface of the ball screw shaft 3. The movable-side connecting male thread portion R312 is formed by a plurality of movable-side connecting threads R312a (second connecting threads) provided on the movable structure 102 side of the outer circumferential surface of the ball screw shaft 3.

[0033] The first actuator 2F rotates the reference ball nut 41 at a predetermined rotational speed, while simultaneously rotating the movable ball nut 61 at a predetermined rotational speed in the opposite direction to the reference ball nut 41. This operation generates a force F1 that separates the movable structure 102 from the reference structure 101, or a force F2 that brings the movable structure 102 closer to the reference structure 101.

[0034] The reference-side conversion mechanism 4 and the reference-side motor 5 can be considered as the first unit actuator 21, which is the smallest unit of the actuator. Similarly, the movable-side conversion mechanism 6 and the movable-side motor 7 can be considered as the second unit actuator 22, which is the smallest unit of another actuator. In this case, the first actuator 2F can be said to be configured such that the first unit actuator 21 is connected in series with the second unit actuator 22. This redundant system, composed of two actuators connected in series with each other, is called a speed-addition type (see Figure 5(b)).

[0035] Focusing again on the reference-side conversion mechanism 4, the reference-side conversion mechanism 4 includes a reference-side ball nut 41, a reference-side gearbox 42, a reference-side radial bearing 43, and a reference-side frame 44.

[0036] The reference-side ball nut 41 can rotate with respect to the ball screw shaft 3. On the inner peripheral surface of the through hole of the reference-side ball nut 41, a reference-side conversion female thread portion R411 (first conversion female thread portion) is provided. The reference-side conversion female thread portion R411 is formed by a plurality of reference-side conversion thread ridges R411a (first conversion thread ridges).

[0037] When the reference-side ball nut 41 rotates, the reference-side ball nut 41 moves translationally relative to the ball screw shaft 3 along the axial direction of the ball screw shaft 3. Since it is a relative translational movement, there is a mode in which the reference-side ball nut 41 moves with respect to the ball screw shaft 3 whose position is held while the position of the ball screw shaft 3 is held. There is also a mode in which the ball screw shaft 3 moves with respect to the reference-side ball nut 41 whose position is held while the position of the reference-side ball nut 41 is held. The reference-side conversion mechanism 4 of the present embodiment adopts the latter mode. That is, the reference-side ball nut 41 rotates with respect to the ball screw shaft 3, but does not move translationally along the axial direction of the ball screw shaft 3.

[0038] The reference-side gear box 42 transmits the torque given from the reference-side motor 5 to the reference-side ball nut 41. The reference-side gear box 42 may be composed of, for example, two gears, or may be composed of a plurality of two or more gears. In the example shown in FIG. 1, the reference-side gear box 42 includes gears 421 and 422. The gear 421 is fixed to the reference-side ball nut 41. When the gear 42l that has received torque from the reference-side motor 5 rotates, the reference-side ball nut 41 rotates.

[0039] The reference-side radial bearing 43 rotatably connects the reference-side ball nut 41 to the reference-side frame 44. An example of the reference-side radial bearing 43 is an angular ball bearing. The inner ring 431 of the reference-side radial bearing 43 is fixed to the outer peripheral surface of the reference-side ball nut 41. The outer ring 432 of the reference-side radial bearing 43 is fixed to the reference-side frame 44.

[0040] The reference-side frame 44 is connected to the reference structure 101. The connection state of the reference-side frame 44 to the reference structure 101 may be a so-called simple support. A simple support means that translation with respect to the reference structure 101 is prohibited, but rotation with respect to the reference structure 101 is permitted. According to such a support state, the reference-side frame 44 can receive a reaction force from the reference structure 101. Note that the connection state of the reference-side frame 44 to the reference structure 101 may be any state as long as it can receive a reaction force from the reference structure 101. For example, it is also possible to adopt a support state called fixed support or movable support.

[0041] The reference-side conversion mechanism 4 constituted by the above elements functions as a rotation-translation conversion unit that converts rotation into translational movement. In the reference-side conversion mechanism 4, the reference-side ball nut 41 rotates with respect to the ball screw shaft 3, but the distance from the reference structure 101 is maintained. As a result, when the reference-side ball nut 41 rotates, the ball screw shaft 3 translates with respect to the reference-side ball nut 41.

[0042] The reference-side motor 5 generates torque for rotating the reference-side ball nut 41. In the example shown in FIG. 1, the reference-side motor 5 is fixed to the reference-side frame 44. That is, similar to the reference-side ball nut 41, the reference-side motor 5 does not move with respect to the reference structure 101, and the distance from the reference structure 101 to the reference-side motor 5 is always maintained.

[0043] The reference-side motor 5 receives three-phase AC power from a power supply unit 55 (see FIG. 4) including an inverter. The power supply unit 55 generates three-phase AC power to be supplied to the reference-side motor 5 according to a control signal C2A provided from a controller 9 (see FIG. 4) described later. The power generated by the power supply unit 55 is supplied to a coil provided in the motor stator 51. Then, a rotating magnetic field is generated according to the three-phase AC supplied to the coil. Due to the interaction between this rotating magnetic field and the magnetic field of the magnet provided in the motor rotor 52, a rotational torque is generated in the motor rotor 52. The rotational torque is applied to the reference-side ball nut 41 via the reference-side gearbox 42.

[0044] The movable-side conversion mechanism 6 differs from the reference-side conversion mechanism 4 in that it is connected to the movable structure 102, but all other elements are the same as those of the reference-side conversion mechanism 4. In other words, the movable-side conversion mechanism 6 includes a movable-side ball nut 61, a movable-side gearbox 62, a movable-side bearing 63, and a movable-side frame 64. A movable-side conversion female thread portion R611 (second conversion female thread portion) is provided on the inner circumferential surface of the through hole of the movable-side ball nut 61. The movable-side conversion female thread portion R611 is formed by a plurality of movable-side conversion threads R611a (second conversion threads).

[0045] In the reference-side conversion mechanism 4, the reference-side ball nut 41 is fixed in position relative to the reference structure 101 and does not move. Instead, the ball screw shaft 3 moves translationally relative to the reference-side ball nut 41.

[0046] In the movable-side conversion mechanism 6, the position of the movable-side ball nut 61 relative to the movable structure 102 is fixed, just as in the reference-side conversion mechanism 4. In other words, the position of the movable-side ball nut 61 relative to the movable structure 102 is preserved. On the other hand, the movable structure 102 can move away from or closer to the reference structure 101. Therefore, the movable-side ball nut 61 of the movable-side conversion mechanism 6 can move translationally with respect to the ball screw shaft 3.

[0047] The second actuator 2S consists of essentially the same parts and has the same structure as the first actuator 2F. Therefore, a detailed explanation of the second actuator 2S is omitted.

[0048] <Autonomous Equilibrium of Frictional Resistance> Here, we will explain the autonomous equilibrium of frictional resistance, which is the basic principle of electric actuators. Figure 2(a) shows the minimum components of an electric actuator. The actuator 100 shown in Figure 2(a) has a first ball nut BN1, a second ball nut BN2, and a ball screw shaft SS. The ball screw shaft SS is not constrained in translational motion or rotation with respect to a predetermined coordinate system. The first ball nut BN1 is rotated by a motor (not shown). As a result, the first ball nut BN1 translates along the axis of the ball screw shaft SS. The second ball nut BN2 is rotated by another motor (not shown). As a result, the second ball nut BN2 translates along the axis of the ball screw shaft SS.

[0049] When the first ball nut BN1 rotates relative to the ball screw shaft SS, the ball screw shaft SS receives a first friction torque from the first ball nut BN1. Similarly, when the second ball nut BN2 rotates relative to the ball screw shaft SS, the ball screw shaft SS receives a second friction torque from the second ball nut BN2.

[0050] Here, we assume an ideal state. That is, we assume that the first friction torque received from the first ball nut BN1 and the second friction torque received from the second ball nut BN2 are perfectly equal. In this case, the first and second friction torques cancel each other out. As a result, no torque acts on the ball screw shaft SS. Consequently, the ball screw shaft SS, whose rotation is not constrained, does not rotate (ω ＳＳ = 0).

[0051] Next, let's consider a realistic scenario. For example, let's assume that the second friction torque received by the ball screw shaft SS from the second ball nut BN2 is greater than the first friction torque received by the ball screw shaft SS from the first ball nut BN1.

[0052] Graph GBN1 in Figure 2(b) shows the relationship between the first friction torque received by the ball screw shaft SS from the first ball nut BN1 and the relative angular velocity. Furthermore, graph GBN2 in Figure 2(b) shows the relationship between the second friction torque received by the ball screw shaft SS from the second ball nut BN2 and the relative angular velocity. Point PBN1s indicates the maximum friction torque of the first ball nut BN1. Point PBN2s indicates the maximum friction torque of the second ball nut BN2.

[0053] In the initial state, the relative angular velocity on the horizontal axis is the angular velocity (ω) applied to the first ball nut BN1, since the ball screw shaft SS is not rotating. １ ) and the angular velocity (ω) applied to the second ball nut BN2 ２ ) is equal to ). The friction torque of the second ball nut BN2 (point PBN2a) is greater than the friction torque of the first ball nut BN1 (point PBN1a). Therefore, the ball screw shaft SS rotates in the same direction as the second ball nut BN2. In other words, the torques received from the first ball nut BN1 and the second ball nut BN2 do not cancel each other out. The ball screw shaft SS is subjected to a net torque (Ts) obtained by subtracting the first friction torque from the second friction torque. The direction of this net torque (Ts) coincides with the direction of rotation of the second ball nut BN2. The net torque (Ts) generates angular acceleration in the ball screw shaft SS. Angular velocity is generated in the ball screw shaft SS, and as the angular velocity increases, the relative angular velocity of the second ball nut BN2 decreases. As a result, the second friction torque of the second ball nut BN2 decreases from point PBN2a to point PBN2b. Meanwhile, the relative angular velocity of the first ball nut BN1 increases. As a result, the first friction torque of the first ball nut BN1 increases, as shown from point PBN1a to point PBN1b. The decreased second friction torque (point PBN2b) and the increased first friction torque (point PBN1b) balance each other at the equilibrium friction torque (Tb). In this state, the net torque (Ts) is zero. In other words, as a result, both the first and second friction torques automatically shift to the equilibrium friction torque (Tb), settling into a state of friction torque equilibrium. This is the autonomous equilibrium phenomenon of friction torque.

[0054] Figure 3(a) shows a state where the initial friction torque of the second ball nut BN2 is extremely large compared to that of the first ball nut BN1. This can be described as the second ball nut BN2 being close to a seized state. Even in this state, the friction torque of the first ball nut BN1 and the friction torque of the second ball nut BN2 autonomously balance out as the ball screw shaft SS rotates. The friction of the second ball nut BN2 transitions from kinetic friction (point PBN2a) to static friction (point PBN2b). The static friction of the second ball nut BN2 (point PBN2b) balances out the dynamic friction torque of the first ball nut BN1 (point PBN1b). When in equilibrium, the second ball nut BN2 and the ball screw shaft SS rotate together. In other words, when in equilibrium, the relative angular velocity between the second ball nut BN2 and the ball screw shaft SS is zero. In other words, the equilibrium state is similar to the operation when the second ball nut BN2 is fixed to the ball screw shaft SS.

[0055] Figure 3(b) shows a state in which the rotation angle of the first ball nut BN1 relative to the reference frame 44 is fixed as a result of the rotation system of the reference side conversion mechanism 4 being fixed. Even in this case, the ball screw shaft SS can rotate relative to the first ball nut BN1 whose rotation angle is fixed, so autonomous equilibrium of friction torque is achieved. The friction of the second ball nut BN2 transitions from dynamic friction (point PBN2a) to static friction (point PBN2b). The static friction of the second ball nut BN2 (point PBN2b) is in equilibrium with the dynamic friction torque of the first ball nut BN1 (point PBN1b). In general, even when the magnitudes of the angular velocities of the first ball nut BN1 and the second ball nut BN2 are different, autonomous equilibrium of friction torque is achieved.

[0056] The speed (v) generated by the actuator 100 with the mechanism shown in Figure 2(a) will now be explained. The relative angular velocity of the first ball nut BN1 is converted into the translational velocity (v1) of the ball screw shaft SS (see equation (1)). The negative sign on the right-hand side of equation (1) is a necessary sign to indicate the translational velocity of the ball screw shaft SS when the translation of the first ball nut BN1 is constrained. v １: Translation speed p of the ball screw shaft SS Ｓ : Lead length ω １ : Angular velocity ω of the first ball nut BN1 ＳＳ : Angular velocity of the ball screw shaft SS

[0057] The relative angular velocity (v2) of the second ball nut BN2 is shown by Equation (2). v ２ : Translation speed p of the ball screw shaft SS Ｓ : Lead length ω ２ : Angular velocity ω of the second ball nut BN2 ＳＳ : Angular velocity of the ball screw shaft SS

[0058] As a result, Equation (3) is obtained.

[0059] From Equation (3), it can be seen that the rotation of the ball screw shaft SS does not affect the speed generated by the actuator 100. The rotation direction of the angular velocity (ω １ ) of the first ball nut BN1 is always opposite to the rotation direction of the angular velocity (ω ２ ) of the second ball nut BN2. It can also be seen that speed addition is established. As shown in Fig. 3(a), even when either the first ball nut BN1 or the second ball nut BN2 is fixed (referred to as "single ball nut fixation"), if the fixed ball nut and the ball screw shaft rotate integrally, speed addition is established. On the other hand, as shown in Fig. 3(b), in the state where the rotation angle of the ball nut is fixed (referred to as "single rotation system fixation"), the maximum generated speed is halved.

[0060] <Functional configuration> Fig. 4 is a diagram focusing on the functions of the electric actuator system 1. The electric actuator system 1 includes sensors 8A and 8B, a controller 9, a first actuator 2F, and a second actuator 2S.

[0061] Sensors 8A and 8B acquire information indicating the state of the movable structure 102 relative to the reference structure 101. Sensors 8A and 8B may, for example, acquire distance information from the reference structure 101 to the movable structure 102. Note that the distance information from the reference structure 101 to the movable structure 102 may be obtained by integrating the rotational speeds of motors 5 and 7. Sensors 8A and 8B may also acquire information as, for example, the angle of the movable structure 102 relative to the reference structure 101. The types of sensors 8A and 8B provided in the electric actuator system 1 are not limited to one, and it is permissible to provide multiple sensors 8A and 8B of the same type. In the example in Figure 4, two sensors 8A and 8B that acquire distance information from the reference structure 101 to the movable structure 102 are shown. Sensor 8A may be included as a component of the first actuator 2F. Sensor 8B may be included as a component of the second actuator 2S. Sensors 8A and 8B pass the acquired information to the controller 9.

[0062] Resolvers 54 and 74 may be provided on the reference motor 5 and the movable motor 7, respectively. These resolvers 54 and 74 allow for obtaining data D54 and D74 related to the rotation of the reference motor 5 and the movable motor 7.

[0063] The controller 9 uses the information received from sensors 8A and 8B to generate a first control signal C2A to be given to the power supply unit 55 for the reference motor 5 and a second control signal C2B to be given to the power supply unit 65 for the movable motor 7. The controller 9 then gives the first control signal C2A to the power supply unit 55 and the second control signal C2B to the power supply unit 65.

[0064] Controller 9 may perform so-called servo control. Controller 9 obtains the difference between the distance obtained from sensors 8A and 8B and the target distance. Then, using this difference, it calculates a control signal value to bring the difference closer to zero.

[0065] For example, let's assume that, in an ideal state, the friction torque generated by the first actuator 2F and the friction torque generated by the second actuator 2S are equal. In this ideal state, the controller 9 makes the content of the control signal C2A given to the first power supply unit 55 and the content of the control signal C2B given to the power supply unit 65 the same. In other words, the content of the control signal C2A given to the power supply unit 55 is the same as the content of the control signal C2B given to the power supply unit 65.

[0066] The configuration illustrated in Figure 4 includes two sensors 8A and 8B. The controller 9 receives first data D8A from the first sensor 8A and second data D8B from the second sensor 8B. For example, the controller 9 may use only the first data D8A and obtain control signals C2A and C2B without using the second data D8B. The controller 9 may use only the second data D8B and obtain control signals C2A and C2B without using the first data D8A. The controller 9 may use both the first data D8A and the second data D8B, and as an example, obtain control signals C2A and C2B using the average value of the first data D8A and the second data D8B.

[0067] The first actuator 2F and the second actuator 2S perform the function of moving the movable structure 102 away from or closer to the reference structure 101. The controller 9 provides control signals C2A and C2B to the power supply unit 55 of the first actuator 2F and the power supply unit 65 of the second actuator 2S, respectively.

[0068] The first actuator 2F includes a reference-side rotation-translation conversion unit 4F, a reference-side drive function unit 5F, a movable-side rotation-translation conversion unit 6F, and a movable-side drive function unit 7F. The reference-side drive function unit 5F performs the function of converting electrical energy into rotational motion energy. The reference-side drive function unit 5F transmits rotational motion to the reference-side rotation-translation conversion unit 4F. The reference-side rotation-translation conversion unit 4F converts rotational motion into translational motion.

[0069] As mentioned above, the electric actuator system 1 may be used in aircraft. Mechanical elements used in aircraft have a specified failure rate. Specifically, the failure rate of the electric actuator system 1 must be lower than the failure rate specified in the specifications.

[0070] The failure rate of the electric actuator system 1 can be estimated using the individual failure rates set for each component that makes up the electric actuator system 1. As shown in Figure 4, the main elements used to estimate the failure rate of the electric actuator system 1 are the ball screw element E3, the bearing element E43, and the gearbox element E42. Strictly speaking, other elements such as the motor controller, sensors (resolvers), cables, and power supply are also taken into consideration, but these are omitted in this explanation. The elements considered in this explanation are mechanical components.

[0071] Each of these elements has a set failure rate. The failure rate can then be estimated by performing calculations using these individual failure rates. If this estimated failure rate is lower than the failure rate required by the higher-level system, the electric actuator system 1 can be adopted as a component of the higher-level system.

[0072] Furthermore, the configuration of the electric actuator system 1 offers the advantageous benefit of not losing its function even if a failure occurs in one of its mechanical components.

[0073] For example, in the ball screw element E3, a first failure mode may occur in which the reference ball nut 41 cannot rotate relative to the ball screw shaft 3 due to jamming between the ball screw shaft 3 and the reference ball nut 41. In the bearing element E43, a second failure mode may occur in which the reference ball nut 41 cannot rotate relative to the ball screw shaft 3 due to jamming between the inner ring 431 and the rolling element 433 or between the outer ring 432 and the rolling element 433. Similarly, as a third failure element, the gearbox element E42 may also experience a third failure mode in which the reference ball nut 41 cannot rotate relative to the ball screw shaft 3 due to jamming between the gears. The electric actuator system 1 can maintain its function as a whole even if any one of these first, second, and third failure modes caused by the mechanical configuration occurs.

[0074] For example, let's assume that a first failure mode occurs in the reference-side conversion mechanism 4. The first failure mode can be considered to be a state in which the initial friction torque between the ball screw shaft 3 and the reference-side ball nut 41 is extremely large. In this case, even if the first failure mode occurs, autonomous equilibrium of the friction torque is achieved, as explained using Figure 3(a). Therefore, the first actuator 2F does not lose its function of moving the movable structure 102 closer to or further away from the reference structure 101. In other words, even if the ball screw shaft 3 and the reference-side ball nut 41 become stuck together, the controller 9 can maintain the function of the first actuator 2F of moving the movable structure 102 closer to or further away from the reference structure 101 by continuing the operation of the reference-side motor 5.

[0075] For example, suppose the ball screw shaft 3 is not fixed to the reference ball nut 41. Then, suppose the controller 9 receives first data D8A(A1) from sensor 8A indicating that the distance from the first reference structure 101 to the movable structure 102 is a predetermined value (A1). Next, the controller 9 decides to change the distance from the reference structure 101 to the movable structure 102 to a different value (A2), and provides a control signal C2A(B2) to the power supply unit 55 to set that value (A2). The control signal C2A(B2) at this time includes an indication that the amount of rotation of the reference drive function unit 5F is a predetermined value (C2).

[0076] Next, let's assume a situation where the ball screw shaft 3 is fixed to the reference ball nut 41. Then, as described above, let's assume that the controller 9 receives first data D8A(A1) from sensor 8A indicating that the distance from the first reference structure 101 to the movable structure 102 is a predetermined value (A1). Next, the controller 9 decides to change the distance from the reference structure 101 to the movable structure 102 to a different value (A2), and provides a control signal C2A(B2) to the power supply unit 55 to set that value (A2). The control signal C2A(B2) at this time includes an indication that the amount of rotation of the reference drive function unit 5F is a predetermined value (C2).

[0077] In short, it is assumed that the data D8A provided to the controller 9 is equivalent whether or not seizing has occurred. Under this assumption, the control signal C2A provided by the controller 9 based on data D8A when there is no seizing between the ball screw shaft 3 and the reference ball nut 41 is equivalent to the control signal C2A provided by the controller 9 based on data D8A when there is seizing between the ball screw shaft 3 and the reference ball nut 41.

[0078] For example, let's assume that a second and a third failure mode occur in the reference-side conversion mechanism 4. The second and third failure modes can be described as a state in which the rotation angle of the reference-side ball nut 41 relative to the reference-side frame 44 is fixed. In that case, even if the second and third failure modes occur, autonomous equilibrium of the friction torque is achieved as explained using Figure 3(b), so the first actuator 2F does not lose its function.

[0079] The above explanation can also be applied to the bearing element E43 and the gearbox element E42. In other words, the first actuator 2F and the second actuator 2S do not lose their function due to failures caused by mechanical elements.

[0080] Incidentally, the failure rate of the electric actuator system 1 is also estimated by taking into account the motor elements E5 caused by the reference motor 5 and the movable motor 7. Failure modes caused by motor elements E5 and E7 can be either stuck (restrained) or unrestrained. For example, if the motor rotor 52 is stuck to the motor stator 51, the shaft of the reference motor 5 cannot rotate. In this state, the reference motor 5 functions as a brake that restrains the rotation of the ball screw shaft 3 via the reference gearbox 42 and the reference ball nut 41. In other words, the state in which the motor rotor 52 is stuck to the motor stator 51 is the same as the state in which the rotation angle of the reference ball nut 41 with respect to the ball screw shaft 3 is fixed. That is, it is the same state as the second and third failure modes described above. Therefore, as explained using Figure 3(b), autonomous equilibrium of friction torque is achieved, and the first actuator 2F does not lose its function.

[0081] On the other hand, let's assume that a coil break occurs in the motor stator 51. In this case, the reference motor 5 cannot generate rotation, and the motor rotor 52 is in a state where it can rotate freely (unconstrained). In this state, as in the first failure mode, the reference ball nut 41 and the ball screw shaft 3 cannot be rotated together in accordance with the rotation of the reference motor 5. Nor can it be said that the rotation angle of the reference ball nut 41 with respect to the ball screw shaft 3 is fixed, as in the second and third failure modes. Therefore, since the reference conversion mechanism 4 is not in a state where autonomous equilibrium of friction torque is achieved, the first actuator 2F loses its function.

[0082] This problem can be addressed by providing a second actuator 2S. Even if the first actuator 2F loses its function, the second actuator 2S can prevent the complete loss of function of the electric actuator system 1.

[0083] In other words, the loss of function of the electric actuator system 1 due to a single failure caused by the aforementioned mechanical configuration can be avoided by the physical configuration. However, it is not possible to avoid the occurrence of an unconstrained failure mode in the motor element E5 by providing a second actuator 2S. The specifications required by higher-level systems vary. For example, if it is required to avoid loss of function due to a certain failure mode (e.g., sticking of a mechanical component), the structure shown in Figure 4 can satisfy that requirement. Sometimes, the requirement is that the occurrence of failure modes be accepted to some extent, but the overall failure rate should be below a certain value. In that case, by providing a second actuator 2S, the failure rate of the electric actuator system 1 can be reduced, making it possible to meet the required failure rate.

[0084] <Effects and Effects> The configuration and effects and effects of the electric actuator system 1 of the embodiment described above are summarized below.

[0085] The electric actuator system 1 changes the relative position of the movable structure 102 with respect to the reference structure 101. The electric actuator system 1 includes a ball screw shaft 3, a reference side ball nut 41 rotatably mounted on the ball screw shaft 3, a reference side conversion mechanism 4 connected to the reference structure 101, a reference side motor 5 that generates torque to rotate the reference side ball nut 41, a movable side conversion mechanism 6 connected to the movable structure 102, a movable side ball nut 61 rotatably mounted on the ball screw shaft 3, and a movable side motor 7 that generates torque to rotate the movable side ball nut 61.

[0086] With this electric actuator system 1, even if a failure occurs due to a mechanical element constituting the reference-side conversion mechanism 4 and the movable-side conversion mechanism 6, the loss of all functions of the electric actuator system 1 can be suppressed. Therefore, the reliability of the electric actuator system 1 can be increased.

[0087] The relative position of the reference ball nut 41 with respect to the reference structure 101 is maintained even when the reference ball nut 41 rotates. The relative position of the movable ball nut 61 with respect to the movable structure 102 is maintained even when the movable ball nut 61 rotates. Therefore, in this embodiment, when viewed in the extending direction of the ball screw shaft 3, the distance between the reference structure 101 and the reference ball nut 41 does not change. The distance between the movable ball nut 61 and the movable structure 102 also does not change. With this structure, forces F1 and F2 that change the relative position of the movable structure 102 with respect to the reference structure 101 can be exerted with a simple configuration.

[0088] The reference-side conversion mechanism 4, reference-side motor 5, movable-side conversion mechanism 6, and movable-side motor 7 constitute the first actuator 2F. The electric actuator system 1 further includes a second actuator 2S connected to the reference structure 101 and the movable structure 102, respectively, in parallel with the first actuator 2F. With this configuration, even if either the first actuator 2F or the second actuator 2S loses its function, the loss of all functions of the electric actuator system 1 can be suppressed. Therefore, reliability can be increased.

[0089] The electric actuator system 1 further includes a controller 9 that generates a first control signal C2A for the reference motor 5 and a second control signal C2B for the movable motor 7. The rotational speed of the reference motor 5 indicated by the first control signal C2A is the same as the rotational speed of the movable motor 7 indicated by the second control signal C2B. With this configuration, it is possible to control the generation of forces F1 and F2 that change the relative position of the movable structure 102 with respect to the reference structure 101.

[0090] Here, we compare the fault tolerance performance of actuator systems employing different types of redundancy. The comparison will focus on actuator system EA1, which employs a force-adding type of redundancy as shown in Figure 5(a); actuator system EA2, which employs a speed-adding type of redundancy as shown in Figure 5(b); and actuator system EA3, which employs both force- and speed-adding type of redundancy as shown in Figure 5(c).

[0091] Actuator system EA1 employing a force-adding redundant system comprises two actuators A1 and A2 connected in parallel. Actuator system EA2 employing a speed-adding redundant system comprises two actuators A1 and A2 connected in series. Actuator system EA3 employing a force-and-speed-adding redundant system comprises two actuators A1 and A2 connected in series, and two further actuators A3 and A4 connected in series.

[0092] Figure 6 is a table summarizing the results of a comparison of the three redundancy methods. The table includes the following columns: "Redundancy Method," "Arrangement of EMA (Electromechanical Actuator) Units," "Stuck Failure of Single Rotational Translation Converter," "Stuck Failure of Single Rotational System," and "Motor Torque Loss Failure of Single Motor." The "Redundancy Method" column lists the three methods described above.

[0093] Each redundancy scheme is equipped with multiple actuators A1 to A4, and in this comparison, we assumed a mode in which all actuators A1 to A4 are in operation (active). In other words, we assumed that two systems of actuators A1 to A4 are always operating. In the "EMA (Electromechanical Actuator) Unit Arrangement" column, an EMA unit refers to the basic configuration of a linear EMA consisting of one motor, one ball screw BS (a set of screw shaft and ball nut), and one set of reduction gears provided as needed. In the speed addition method column, it is written as "series." This does not mean a configuration in which two EMAs are simply arranged in series. To shorten the overall length, we assumed a configuration in which two sets of ball screw BS are nested together, like the tube of a telescope.

[0094] Furthermore, there is also a Differential BS system with a configuration similar to the Nested BS. On the other hand, as a method of speed addition, it is also possible to use a system consisting of one BS, one planetary gear, and two motors. In this case, the rotational speeds of the two motors can be added together by the planetary gear and then converted to rotational translation by the BS. However, planetary gears have many bearings, which increases the chances of seizing and failure. Therefore, they will not be considered in this comparison.

[0095] The column for the speed-force addition method states "series + parallel". This refers to the electric actuator system 1 of the embodiment shown in Figure 1, etc. Specifically, the electric actuator system 1 has two nut mechanisms on one ball screw shaft. A nut mechanism is a mechanism equipped with a gear for rotating the nut and a bearing for holding the nut in the axial load support housing while allowing it to rotate. The electric actuator system 1 mounts one or more motors on each nut mechanism to rotate the nuts, so that the housing equipped on one nut generates an output speed that is the speed added to the other. One ball screw shaft is freely rotatable and supported by two nuts. In this state, one ball screw shaft transmits the axial load. The rotation generated on the ball screw shaft has the function of autonomously balancing the frictional resistance of both nut parts.

[0096] "Single rotational translation converter seizure failure" refers to a seizure failure in the rotational translation converter of either of the two EMA units. In other words, "single rotational translation converter seizure failure" means seizure at a single nut. A single nut becomes fused with the screw shaft it contacts due to seizing or ball damage, making relative translational motion impossible. In this column, "○" means that it has failure resistance. In other words, "○" means that it can maintain its function. On the other hand, in this column, "×" means that the EMA has failed. In other words, "×" means that it is in a fixed state and will be a fatal condition when applied to a rudder surface.

[0097] The following was observed when comparing the "single rotation translation conversion unit seizure failure" across each redundancy method: • Speed ​​addition method: ○ (However, the maximum generated speed is halved.) • Force addition method: × (No clutch), ○ (With clutch, maximum generated speed is halved.) • Speed-force addition method: ○ (Performance can be maintained. Both the maximum generated speed and maximum generated force can be maintained.) In the force addition method, in the configuration with a clutch, the clutch equipped on the faulty EMA unit was removed to detach it from the load side.

[0098] "Single rotational system seizure failure" refers to a seizure failure occurring in the rotational system of either of the two EMA units. In other words, it is a failure mode in which a ball bearing or similar component seizes, resulting in a state where the motor's torque and / or rotational speed are not transmitted to one motor and one ball screw BS. In this column, "○" means that it has failure tolerance. In other words, "○" means that it can maintain its function. On the other hand, in this column, "×" means that the EMA has failed. In other words, "×" means that it is in a fixed state, which would be a fatal condition if applied to a rudder surface.

[0099] The following was found when comparing "single rotation system seizure failures" using each redundancy method: ・Speed ​​addition method: ○ (However, the maximum generated speed is halved.) ・Force addition method: × (No clutch), ○ (With clutch, maximum generated speed is halved.) ・Speed-force addition method: ○ (However, the maximum generated speed is halved.) "Single motor torque loss failure" is a failure in which the electromagnetic torque of either of the two EMA units is lost. In other words, it is a failure mode such as torque loss failure caused by the loss of power supplied to the motor, or power interruption during fault response due to failure of windings and / or power electronics, etc. In this column, "○" means that it has fault tolerance. In other words, "○" means that it can maintain operation. On the other hand, in this column, "×" means that the EMA has failed. In other words, "×" means that the generated force is lost.

[0100] The following was observed when comparing the "motor torque loss failure of a single motor" using each redundancy method: • Speed ​​addition method: × (no brake), ○ (with brake, however the maximum generated speed is halved.) • Force addition method: ○ (however, the maximum generated speed is halved.) • Speed-force addition method: ○ (however, the maximum generated speed is halved.) In the speed addition method, it was assumed that braking was performed by the brake equipped on the EMA unit of the faulty side, and the force generated by the healthy side was transmitted.

[0101] The results of our investigation into each redundancy method are summarized below. The speed addition method tends to have a complex structure because a brake is an essential component. The speed addition method has reliability issues with its brake. For example, when applied to steering surface drive, it is subjected to harsh conditions due to its high output. The force addition method tends to have a complex structure because a clutch is an essential component. The force addition method has reliability issues with its clutch. For example, when applied to steering surface drive, it is subjected to harsh conditions due to its high output.

[0102] The speed-force addition method (in this embodiment) does not require brakes and clutches as essential components. Therefore, by adopting the speed-force addition method, a relatively simple structure can be achieved. And high reliability can be ensured. For example, by adopting the speed-force addition method, 10 －９ Reliability below FPH can be achieved. When adopting a speed-force addition method, the advantage that performance degradation does not occur in the event of a sticking failure in the single rotation translation conversion section may be emphasized. In this case, it becomes possible to design the motor with half the maximum torque and maximum speed. For example, if it is assumed that the system is operated within a range of 50% or less of the required specifications for maximum generated force and maximum generated speed when shared, the design will tolerate both single rotation system sticking and single motor torque loss failures. As a result, the actuator system can be made lighter.

[0103] <Second Embodiment> The physical configuration of the actuator utilizing the autonomous equilibrium of friction torque is not limited to that of the first embodiment. Figure 7 shows the configuration of an electric actuator system 1A, which is another example of the physical configuration of an actuator utilizing the autonomous equilibrium of friction torque. The electric actuator system 1A of the second embodiment will be described below with reference to Figure 7. The electric actuator system 1A includes a first actuator 2AF and a second actuator 2AS. Note that a detailed illustration of the second actuator 2AS is omitted in Figure 7.

[0104] The first actuator 2AF includes a connecting nut 32A (first connecting part), a reference-side conversion mechanism 4A, a reference-side motor 5A (first motor), a movable-side conversion mechanism 6A, and a movable-side motor 7A (second motor). Furthermore, the reference-side conversion mechanism 4A includes a reference-side screw shaft 41A (first conversion part, first conversion screw shaft), and the movable-side conversion mechanism 6A includes a movable-side screw shaft 61A (second conversion part, second conversion screw shaft).

[0105] In the second embodiment, a mechanism using an Acme screw or a mechanism using a roller screw may be used as the mechanism for converting rotation to translation.

[0106] The connecting nut 32A is a cylindrical member having a through hole. The through hole extends from the base structure 101 side to the movable structure 102 side of the connecting nut 32A. A connecting female thread portion C32 is provided on the inner circumferential surface of the through hole. The connecting female thread portion C32 may be formed by a plurality of threads that are continuous from the base structure 101 side to the movable structure 102 side of the connecting nut 32A. The connecting female thread portion C32 may be formed by a plurality of threads provided on the base structure 101 side of the connecting nut 32A and a plurality of threads provided on the movable structure 102 side. In this case, the inner circumferential surface of the through hole includes a portion with a plurality of threads and a portion without a plurality of threads. In the example in Figure 7, it is shown as a plurality of threads that are continuous from the base structure 101 side to the movable structure 102 side of the connecting nut 32A.

[0107] The connecting female thread portion C32 includes a reference side connecting female thread portion C321 and a movable side connecting female thread portion C322. The reference side connecting female thread portion C321 (first connecting female thread portion) is a portion formed by a plurality of reference side connecting threads C321a (first connecting threads) provided on the reference side conversion mechanism 4A side of the connecting nut 32A. The reference side screw shaft 41A, which will be described later, is screwed into the reference side connecting female thread portion C321. The movable side connecting female thread portion C322 (second connecting female thread portion) is a portion formed by a plurality of movable side connecting threads C322a (second connecting threads) provided on the movable side conversion mechanism 6A side of the connecting nut 32A. The movable side screw shaft 61A, which will be described later, is screwed into the movable side connecting female thread portion C322.

[0108] The first actuator 2AF rotates the reference screw shaft 41A at a predetermined rotational speed, while simultaneously rotating the movable screw shaft 61A at a predetermined rotational speed in the opposite direction to the reference screw shaft 41A. This operation generates a force F1 that separates the movable structure 102 from the reference structure 101, or a force F2 that brings the movable structure 102 closer to the reference structure 101.

[0109] The reference-side conversion mechanism 4A includes a reference-side screw shaft 41A, a reference-side gearbox 42A, a reference-side thrust bearing 43A, and a reference-side frame 44A. The reference-side screw shaft 41A can rotate relative to the connecting nut 32A. The outer circumferential surface of the reference-side screw shaft 41A is provided with a reference-side conversion male screw portion C411 (first conversion male screw portion). The reference-side conversion male screw portion C411 is formed by a plurality of reference-side conversion threads C411a (first conversion threads). When the reference-side screw shaft 41A rotates, the reference-side screw shaft 41A moves translationally relative to the connecting nut 32A along the axial direction of the connecting nut 32A.

[0110] The reference gearbox 42A transmits the torque supplied by the reference motor 5A to the reference screw shaft 41A. The reference gearbox 42A includes gears 421A and 422A. Gear 421A is fixed to the reference screw shaft 41A. When gear 421A rotates after receiving torque from the reference motor 5A, the reference screw shaft 41A rotates.

[0111] The reference thrust bearing 43A rotatably connects the reference screw shaft 41A to the reference frame 44A. The end of the reference screw shaft 41A is fixed to the shaft raceway plate 431A of the reference thrust bearing 43A. The frame raceway plate 432A of the reference thrust bearing 43A is fixed to the reference frame 44A.

[0112] The reference frame 44A is connected to the reference structure 101. The manner of connection between the reference frame 44A and the reference structure 101 is the same as in the first embodiment, so a detailed explanation is omitted.

[0113] The reference motor 5A generates torque to rotate the reference screw shaft 41A. The other components of the reference motor 5A are the same as in the first embodiment, so a detailed explanation is omitted.

[0114] In the movable-side conversion mechanism 6A, the position of the movable-side screw shaft 61A relative to the movable structure 102 is maintained, just as in the reference-side conversion mechanism 4A. In other words, the position of the movable-side screw shaft 61A relative to the movable structure 102 is preserved. On the other hand, the movable structure 102 can move away from or closer to the reference structure 101. Therefore, the movable-side screw shaft 61A of the movable-side conversion mechanism 6A can move translationally with respect to the connecting nut 32A.

[0115] The movable-side conversion mechanism 6A includes a movable-side screw shaft 61A, a movable-side gearbox 62A, a movable-side thrust bearing 63A, and a movable-side frame 64A. The outer circumferential surface of the movable-side screw shaft 61A is provided with a movable-side conversion male screw portion C611 (second conversion male screw portion). The movable-side conversion male screw portion C611 is formed by a plurality of movable-side conversion threads C611a (second conversion threads). Since the physical shape and structure of these are generally the same as those of the reference-side conversion mechanism 4A, a detailed explanation will be omitted.

[0116] <Effects> In the electric actuator system 1A of the second embodiment, even if there is a difference between the friction torque between the connecting nut 32A and the reference side screw shaft 41A and the friction torque between the connecting nut 32A and the movable side screw shaft 61A, the rotation of the connecting nut 32A causes the friction torque to autonomously reach an equilibrium state.

[0117] <Third Embodiment> Figure 8 shows the configuration of an electric actuator system 1B, which is yet another example of the physical configuration of an actuator that utilizes the autonomous equilibrium of friction torque. The electric actuator system 1B of the third embodiment will be described below with reference to Figure 8. The electric actuator system 1B includes a first actuator 2BF and a second actuator 2BS.

[0118] The first actuator 2BF includes a connecting module 3B (first connecting part), a reference-side conversion mechanism 4B, a reference-side motor 5B (first motor), a movable-side conversion mechanism 6B, and a movable-side motor 7B (second motor). Furthermore, the reference-side conversion mechanism 4B includes a reference-side nut 41B (first conversion part, first conversion nut), and the movable-side conversion mechanism 6B includes a movable-side screw shaft 61B (second conversion part, second conversion screw shaft).

[0119] In other words, the mechanism for converting rotation to translation in the first actuator 2BF differs between the reference-side conversion mechanism 4B and the movable-side conversion mechanism 6B. The reference-side conversion mechanism 4B generates translation of the connecting screw shaft 31B by rotating the reference-side nut 41B. The movable-side conversion mechanism 6B generates translation of the movable-side screw shaft 61B by rotating the movable-side screw shaft 61B.

[0120] The reference-side conversion mechanism 4B includes a reference-side nut 41B, a reference-side gearbox 42B, a reference-side radial bearing 43B, and a reference-side frame 44B. The reference-side nut 41B is provided with a reference-side conversion female thread portion P41 (first conversion female thread portion) on the inner circumferential surface of the through hole. The reference-side conversion female thread portion P41 is formed by a plurality of reference-side conversion threads P41a (first conversion threads). The other shapes and structures are the same as those of the reference-side conversion mechanism 4 in the first embodiment. Therefore, a further detailed description of the reference-side conversion mechanism 4B is omitted.

[0121] The movable side conversion mechanism 6B includes a movable side screw shaft 61B, a movable side gearbox 62B, a movable side thrust bearing 63B, and a movable side frame 64B. The movable side screw shaft 61B is provided with a movable side conversion male screw portion P63 (second conversion male screw portion) on its outer circumferential surface. The movable side conversion male screw portion P63 is formed by a plurality of movable side conversion threads P63a (second conversion threads). These shapes and structures are the same as those of the movable side conversion mechanism 6A of the second embodiment. Therefore, further detailed description of the movable side conversion mechanism 6B is omitted.

[0122] The connecting module 3B includes a connecting screw shaft 31B and a connecting nut 32B.

[0123] The side of the connecting screw shaft 31B facing the reference structure 101 is screwed into the reference side nut 41B of the reference side conversion mechanism 4B. The side of the connecting screw shaft 31B facing the movable structure 102 is screwed into the connecting nut 32B. In other words, a connecting male thread portion P31 is provided on the outer circumferential surface of the connecting screw shaft 31B. The side of the connecting male thread portion P31 facing the reference structure 101 (reference side connecting male thread portion P311) engages with the reference side connecting female thread portion P321 of the reference side nut 41B. The reference side connecting male thread portion P311 is formed by a plurality of reference side connecting threads P311a (first connecting threads). The side of the connecting male thread portion P31 facing the movable structure 102 (movable side connecting male thread portion P312) engages with the reference side connecting female thread portion P321 of the connecting nut 32B, which will be described later. The movable side connecting male thread portion P312 is formed by a plurality of movable side connecting threads P312a.

[0124] A connecting screw shaft 31B is screwed into the reference structure 101 side of the connecting nut 32B. The movable side screw shaft 61B of the movable side conversion mechanism 6B is screwed into the movable structure 102 side of the connecting nut 32B. In other words, a connecting female screw portion P32 is provided on the inner circumferential surface of the through hole formed in the connecting nut 32B. The reference structure 101 side of the connecting female screw portion P32 (reference side connecting female screw portion P321) engages with the connecting male screw portion P31 of the connecting screw shaft 31B. The reference side connecting female screw portion P321 is formed by a plurality of reference side connecting threads P321a. The movable structure 102 side of the connecting female screw portion P32 (movable side connecting female screw portion P322) engages with the movable side conversion male screw portion P63. The movable side connecting female screw portion P322 is formed by a plurality of movable side connecting threads P322a (second connecting threads).

[0125] <Effects> In the third embodiment of the electric actuator system 1B, even if there is a difference between the friction torque between the connecting screw shaft 31B and the reference side nut 41B and the friction torque between the connecting nut 32B and the movable side screw shaft 61B, the rotation of the connecting screw shaft 31B and the connecting nut 32B causes the friction torque to autonomously reach an equilibrium state.

[0126] <Modification> The electric actuator system of this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the claims.

[0127] Figure 9 shows the physical configuration of the first modified electric actuator system 1C. As shown in Figure 9, the electric actuator system 1C includes an actuator 2C, a sensor 8C, and a controller 9. The actuator 2C of the first modified configuration further includes a reference-side sub-motor 5S (first sub-motor) and a movable-side sub-motor 7S (second sub-motor) in addition to the components of the first actuator 2F of the first embodiment. The reference-side sub-motor 5S provides torque to the reference-side gearbox 42 of the reference-side conversion mechanism 4. The movable-side sub-motor 7S provides torque to the movable-side gearbox 62 of the movable-side conversion mechanism 6. This configuration also improves the reliability of the electric actuator system 1C.

[0128] Figure 10 shows the physical configuration of the second modified electric actuator system 1D. As shown in Figure 10, the electric actuator system 1D includes an actuator 2D, a sensor 8D, and a controller 9. The actuator 2D of the second modified example has a reference side composite motor 5D (first composite motor) instead of the reference side motor 5 of the first embodiment, and a movable side composite motor 7D (second composite motor) instead of the movable side motor 7. The reference side composite motor 5D has a pair of motor coils 511 and 512 that are independent of each other. The movable side composite motor 7D has a pair of motor coils 711 and 712 that are independent of each other. For example, even if a failure such as a break in the wire occurs in one of the motor coils 511, the other motor coil 512 can prevent the loss of motor function. This configuration also improves the reliability of the electric actuator system 1D.

[0129] [Note] This disclosure includes the following configuration.

[0130] This disclosure is "1" an electric actuator system for relatively changing the position of a second structure relative to a first structure along a translation axis, comprising: a first motor for generating rotational torque; a first conversion unit rotatably connected to the first structure and including a first conversion screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the first motor; a second motor for generating rotational torque; a second conversion unit rotatably connected to the second structure and including a second conversion screw thread for causing translation in the direction of the translation axis by rotating in accordance with the torque generated by the second motor; and a first connecting unit extending from the first conversion unit toward the second conversion unit and including a first connecting screw thread that engages with the first conversion screw thread and a second connecting screw thread that engages with the second conversion screw thread."

[0131] This disclosure is "2" "the electric actuator system according to [1] above, wherein the relative position of the first transformer with respect to the first structure is maintained even when the first transformer rotates, and the relative position of the second transformer with respect to the second structure is maintained even when the second transformer rotates."

[0132] This disclosure includes, "3" the first motor, the first converter, the second motor, the second converter and the first connector, which constitute a first actuator, and further comprising a second actuator connected to the first structure and the second structure respectively so as to be in parallel with the first actuator, the second actuator comprising: a third motor that generates rotational torque; a third converter rotatably connected to the first structure and including a third converter screw thread for causing the translation in the direction of the translation axis by rotating in accordance with the torque generated by the third motor; a fourth motor that generates rotational torque; and a fourth converter rotatably connected to the second structure and including a fourth converter screw thread for causing the translation in the direction of the translation axis by rotating in accordance with the torque generated by the fourth motor. The electric actuator system according to [1] or [2] above, further comprising: a second connecting portion extending from the third conversion portion toward the fourth conversion portion and including a third connecting screw thread that engages with the third conversion screw thread and a fourth connecting screw thread that engages with the fourth conversion screw thread.

[0133] This disclosure is "4" an electric actuator system according to any one of the above [1] to [3], further comprising a first sub-motor that generates torque to rotate the first conversion unit, and a second sub-motor that generates torque to rotate the second conversion unit."

[0134] This disclosure is "5" "an electric actuator system according to any one of the above [1] to [4], further comprising a controller for generating a first control signal for a first motor and a second control signal for a second motor, wherein the rotational speed of the first motor indicated by the first control signal is the same as the rotational speed of the second motor indicated by the second control signal."

[0135] This disclosure is "6" an electric actuator system according to any one of the above [1] to [5], further comprising a controller for generating a first control signal and a third control signal for the first motor, the controller generating the first control signal when the first converter is in a state where it can rotate relative to the first coupling, the controller generating the third control signal when the first converter is in a state where it cannot rotate relative to the first coupling, and the rotational speed of the first motor indicated by the first control signal is the same as the rotational speed of the first motor indicated by the third control signal."

[0136] This disclosure is "7" "The electric actuator system according to any one of the above [1] to [6], wherein the first connecting portion is a connecting screw shaft including a first connecting male screw portion formed by the first connecting screw thread and a second connecting male screw portion formed by the second connecting screw thread, the first conversion portion is a first conversion nut including a through hole through which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole is provided with a first conversion female screw portion formed by the first conversion screw thread, and the second conversion portion is a second conversion nut including a through hole through which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole is provided with a second conversion female screw portion formed by the second conversion screw thread."

[0137] This disclosure includes "8" "the electric actuator system according to [7] above, wherein the connecting screw shaft is a ball screw shaft, and each of the first conversion nut and the second conversion nut is a ball nut."

[0138] This disclosure is "9" "an electric actuator system according to any one of the above [1] to [6], wherein the first conversion part is a first conversion screw shaft including a first conversion male screw portion formed by the first conversion screw thread, the second conversion part is a second conversion screw shaft including a second conversion male screw portion formed by the second conversion screw thread, and the first connecting part is a connecting nut including a through hole through which the first conversion screw shaft and the second conversion screw shaft are inserted, and the inner circumferential surface of the through hole is provided with a first connecting female screw portion formed by the first connecting screw thread and a second connecting female screw portion formed by the second connecting screw thread."

[0139] This disclosure is "10" "an electric actuator system according to any one of the above [1] to [6], wherein the first connecting portion includes a connecting screw shaft including a connecting male screw portion formed by the first connecting screw threads, and a connecting nut including a through hole into which the connecting screw shaft is inserted and the inner circumferential surface of the through hole includes a connecting female screw portion formed by the second connecting screw threads, the first conversion portion is a first conversion nut including a through hole through which the connecting screw shaft is inserted and the inner circumferential surface of the through hole is provided with a first conversion female screw portion formed by the first conversion screw threads, and the second conversion portion is a second conversion screw shaft including a second conversion male screw portion formed by the second conversion screw threads."

[0140] 1, 1A, 1B, 1C, 1D Electric actuator system 2F, 2AF, 2BF First actuator 2S, 2AS, 2BS Second actuator 2C, 2D Actuator 3 Ball screw shaft (first connecting part, connecting screw shaft) 3B Connecting module (first connecting part) 4, 4A, 4B Reference side conversion mechanism 5, 5A, 5B Reference side motor (first motor) 5D Reference side composite motor (first composite motor) 5S Reference side sub-motor (first sub-motor) 6, 6A, 6B Movable side conversion mechanism 7, 7A, 7B Movable side motor (second motor) 7D Movable side composite motor (second composite motor) 7S Movable side sub-motor (second sub-motor) 8A, 8B, 8C, 8D Sensor 9 Controller 31B Connecting screw shaft 32A Connecting nut (first connecting part) 32B Connecting nut R31 Connecting male thread part R311 Reference side connecting male thread part (first connecting male thread part) R311a Reference side connecting thread (first connecting thread) R312 Movable side connecting male thread part (second connecting male thread part) R312a Movable side connecting thread (second connecting thread) C32 Connecting female thread part C321 Reference side connecting female thread part (first connecting female thread part) C321a Reference side connecting thread (first connecting thread) C322 Movable side connecting female thread part (second connecting female thread part) C322a Movable side connecting thread (second connecting thread) P32 Connecting female thread part P311 Reference side connecting male thread part P311a Reference side connecting thread (first connecting thread) P312 Movable side connecting male thread P312a ​​Movable side connecting thread P321 Reference side connecting female thread P321a Reference side connecting thread P322 Movable side connecting female thread P322a Movable side connecting thread (second connecting thread) 41 Reference side ball nut (first conversion part, first conversion nut) 41A Reference side screw shaft (first conversion part, first conversion screw shaft) 41B Reference side nut (first conversion part, first conversion nut) 42, 42A, 42B Reference side gearbox 43, 43B Reference side radial bearing 43A Reference side thrust bearing 44, 44A,44B Reference side frame R411 Reference side conversion female thread section (first conversion female thread section) R411a Reference side conversion thread (first conversion thread) C411 Reference side conversion male thread section (first conversion male thread section) C411a Reference side conversion thread (first conversion thread) P41 Reference side conversion female thread section (first conversion female thread section) P41a Reference side conversion thread (first conversion thread) 61 Movable side ball nut (second conversion section, second conversion nut) 61A, 61B Movable side screw shaft (second conversion section, second conversion screw shaft) R611 Movable side conversion female thread section (second conversion female thread section) R611a Movable side conversion thread (second conversion thread) C611 Movable side conversion male thread section (second conversion male thread section) C611a Movable side conversion thread (second conversion thread) P63 Movable side conversion male thread part (second conversion male thread part) P63a Movable side conversion thread (second conversion thread),

Claims

1. An electric actuator system for relatively changing the position of a second structure with respect to a first structure along a translation axis, comprising: a first motor for generating rotational torque; a first conversion unit rotatably connected to the first structure and including a first conversion screw thread for causing translation along the direction of the translation axis by rotating in accordance with the torque generated by the first motor; a second motor for generating rotational torque; a second conversion unit rotatably connected to the second structure and including a second conversion screw thread for causing translation along the direction of the translation axis by rotating in accordance with the torque generated by the second motor; and a first connecting unit extending from the first conversion unit toward the second conversion unit and including a first connecting screw thread that engages with the first conversion screw thread and a second connecting screw thread that engages with the second conversion screw thread.

2. The electric actuator system according to claim 1, wherein the relative position of the first transformer with respect to the first structure is maintained even when the first transformer rotates, and the relative position of the second transformer with respect to the second structure is maintained even when the second transformer rotates.

3. The first motor, the first converter, the second motor, the second converter, and the first connector constitute a first actuator, and further comprising a second actuator connected to the first structure and the second structure respectively so as to be in parallel with the first actuator, the second actuator includes a third motor that generates rotational torque, a third converter rotatably connected to the first structure and including a third converter screw thread for causing the translation in the direction of the translation axis by rotating in accordance with the torque generated by the third motor, a fourth motor that generates rotational torque, and a fourth converter rotatably connected to the second structure and including a fourth converter screw thread for causing the translation in the direction of the translation axis by rotating in accordance with the torque generated by the fourth motor, The electric actuator system according to claim 1, further comprising: a second connecting portion extending from the third conversion portion toward the fourth conversion portion and including a third connecting screw thread that engages with the third conversion screw thread and a fourth connecting screw thread that engages with the fourth conversion screw thread.

4. The electric actuator system according to any one of claims 1 to 3, further comprising: a first sub-motor that generates torque for rotating the first conversion unit; and a second sub-motor that generates torque for rotating the second conversion unit.

5. The electric actuator system according to claim 1, further comprising a controller that generates a first control signal for the first motor and a second control signal for the second motor, wherein the rotational speed of the first motor indicated by the first control signal is the same as the rotational speed of the second motor indicated by the second control signal.

6. The electric actuator system according to claim 1, further comprising a controller for generating a first control signal and a third control signal for the first motor, wherein the first control signal is generated when the first converter is rotatable relative to the first coupling portion, and the third control signal is generated when the first converter is not rotatable relative to the first coupling portion, and the rotational speed of the first motor indicated by the first control signal is the same as the rotational speed of the first motor indicated by the third control signal.

7. The electric actuator system according to claim 1, wherein the first connecting portion is a connecting screw shaft including a first connecting male screw portion formed by the first connecting screw thread and a second connecting male screw portion formed by the second connecting screw thread; the first conversion portion is a first conversion nut including a through hole through which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole is provided with a first conversion female screw portion formed by the first conversion screw thread; and the second conversion portion is a second conversion nut including a through hole through which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole is provided with a second conversion female screw portion formed by the second conversion screw thread.

8. The electric actuator system according to claim 7, wherein the connecting screw shaft is a ball screw shaft, and each of the first conversion nut and the second conversion nut is a ball nut.

9. The electric actuator system according to claim 1, wherein the first conversion part is a first conversion screw shaft including a first conversion male screw portion formed by the first conversion screw thread, the second conversion part is a second conversion screw shaft including a second conversion male screw portion formed by the second conversion screw thread, and the first connecting part is a connecting nut including a through hole through which the first conversion screw shaft and the second conversion screw shaft are inserted, and the inner circumferential surface of the through hole is provided with a first connecting female screw portion formed by the first connecting screw thread and a second connecting female screw portion formed by the second connecting screw thread.

10. The electric actuator system according to claim 1, wherein the first connecting portion includes a connecting screw shaft including a connecting male thread formed by the first connecting screw thread, and a connecting nut including a through hole into which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole includes a connecting female thread formed by the second connecting screw thread, the first conversion portion is a first conversion nut including a through hole through which the connecting screw shaft is inserted, and the inner circumferential surface of the through hole is provided with a first conversion female thread formed by the first conversion screw thread, and the second conversion portion is a second conversion screw shaft including a second conversion male thread formed by the second conversion screw thread.

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