Electric linear motion actuator

1. An electric linear motion actuator comprising:

an electric motor;

a linear moving member capable of moving between a standby position where the linear moving member is spaced apart from a target with a predetermined clearance between the linear moving member and the target and a load applying position where the linear moving member contacts the target to apply a load to the target;

a motion converting mechanism that converts a rotational motion of the electric motor into a linear motion of the linear moving member;

a load sensor that detects a magnitude of the load applied to the target from the linear moving member; and

a controller configured to perform a feedback control in which based on a difference between the load detected by the load sensor and a load command value, the electric motor is controlled so that the load applied from the linear moving member to the target becomes equal to the load command value,

wherein the controller comprises an overshoot suppression control means configured to reduce a number of revolutions of the electric motor when the linear moving member moves from the standby position toward the load applying position to apply a load to the target and moves into a predetermined zone immediately before the position where the clearance between the linear moving member and the target becomes zero.

2. The electric linear motion actuator of claim 1 , further comprising a rotation angle sensor that detects a rotation angle of the electric motor;

wherein the overshoot suppression control means is configured to determine whether the linear moving member has moved into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero, on the basis of the rotation angle of the electric motor detected by the rotation angle sensor.

3. The electric linear motion actuator of claim 2 , wherein the overshoot suppression control means is configured to calculate a range of the rotation angle of the electric motor corresponding to the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero, based on a magnitude of a predetermined load detected by the load sensor while the linear moving member is applying a load to the target, and with reference to a rotation angle of the electric motor detected by the rotation angle sensor when the magnitude of the predetermined load is detected by the load sensor; and

the overshoot suppression control means is further configured to determine that the linear moving member has moved into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero, when the rotation angle of the electric motor detected by the rotation angle sensor moves within the range of the rotation angle.

4. The electric linear motion actuator of claim 1 , wherein the overshoot suppression control means is configured to change a voltage applied to the electric motor such that the number of revolutions of the electric motor decreases, when the linear moving member moves into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero.

5. The electric linear motion actuator of claim 1 , wherein the overshoot suppression control means is configured to reduce a voltage to be applied to the electric motor to a predetermined value, when the linear moving member moves into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero.

6. The electric linear motion actuator of claim 1 , wherein the overshoot suppression control means is configured to perform feedback control on the electric motor in which based on a difference between the number of revolutions of the electric motor and a predetermined small number of revolutions, the number of revolutions of the electric motor is reduced to the predetermined small number of revolutions, when the linear moving member moves into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero.

7. The electric linear motion actuator of any one of claim 1 , wherein the electric motor is configured to be driven by a pulse voltage generated by repeatedly and discontinuously applying a constant voltage; and

the overshoot suppression control means is configured to reduce a ratio of a turned-on time during which the constant voltage is being applied to a sum of the turned-on time and a turned-off time during which the constant voltage is not being applied, when the linear moving member moves into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero.

8. The electric linear motion actuator of claim 1 , wherein the electric motor is driven by a pulse voltage generated by being repeatedly turned on and turned off; and

the overshoot suppression control means is configured to reduce a pulse amplitude of the pulse voltage, which is applied to the electric motor, when the linear moving member moves into the predetermined zone, which is immediately before the position where the clearance between the linear moving member and the target becomes zero.