Head-up display device

1. A head-up display device mounted on a moving body that projects an image on a projection member to virtually display the image to be visible to a passenger, comprising:

a projector that projects display light;

a reflector mirror that reflects the display light from the projector toward the projection member;

a stepper motor that outputs rotation;

a reduction gear mechanism formed of a plurality of gears, the reduction gear mechanism reducing the rotation which is output from the stepper motor and transmitted to the reflector mirror; and

a controller that, based on a control instruction from the passenger, calculates a control step angle that controls the rotation of the stepper motor, wherein

the controller includes

a determiner that determines whether an output direction of the rotation to be output from the stepper motor according to the control instruction at this determination is the same direction or the opposite direction as a direction of the rotation to be output from the stepper motor according to the control instruction at the last determination, and

a reverse direction adder that

defines a reference step angle as a step angle that the stepper motor rotates by in accordance with a determination of the same direction by the determiner, and

when the determiner determines the opposite direction, adds a reverse step angle of the opposite direction to the control step angle, the reverse step angle of the opposite direction being equal to or greater than a sum of the reference step angle and a backlash angle of the reduction gear mechanism.

2. The head-up display device of claim 1 , wherein

the controller includes a same direction adder that, when the determiner determines the same direction, adds the reference step angle of the same direction to the control step angle.

3. The head-up display device of claim 1 , further comprising:

a memory unit that stores the control step angle and a correction parameter for correcting the control step angle, wherein

the controller includes

an updater that updates the control step angle with the correction parameter, and

an overwriter that, when the determiner determines the opposite direction, overwrites the correction parameter based on a slippage estimated from the backlash angle with respect to the control step angle.

4. The head-up display device of claim 3 , wherein

the when the determiner determines the same direction, the overwriter maintains the correction parameter as is.

5. The head-up display device of claim 3 , wherein

the controller includes

a resetter that rotates the reflector mirror in a reset direction where the image moves toward an outside-of-display region to reset display of the image, and

an initialization position setter that rotates the reflector mirror in an initialization direction from the outside-of-display region toward an initialization position to begin display of the image, and

the overwriter is configured to

when the determiner determines the same direction, maintain the correction parameter as is,

when the determiner determines the opposite direction, and when the output direction matches the initialization direction, set the correction parameter to 0, and

when the determiner determines the opposite direction, and when the output direction does not match the initialization direction, set the correction parameter to be equal in magnitude to the backlash angle.

6. The head-up display device of claim 5 , wherein

the reset direction is a down-corresponding direction that causes the image to move in a down direction of the moving body,

the initialization direction is an up-corresponding direction that causes the image to move in an up direction of the moving body, and

the overwriter is configured to

when the determiner determines the same direction, maintain the correction parameter as is,

when the determiner determines the opposite direction, and when the output direction is the down-corresponding direction, set the correction parameter to be equal in magnitude to the backlash angle, and

when the determiner determines the opposite direction, and when the output direction is the up-corresponding direction, set the correction parameter to 0.

7. The head-up display device of claim 5 , wherein

the reset direction is an up-corresponding direction that causes the image to move in an up direction of the moving body,

the initialization direction is a down-corresponding direction that causes the image to move in a down direction of the moving body, and

the overwriter is configured to

the when the determiner determines the same direction, maintain the correction parameter as is,

when the determiner determines the opposite direction, and when the output direction is the up-corresponding direction, set the correction parameter to be equal in magnitude to the backlash angle, and

when the determiner determines the opposite direction, and when the output direction is the down-corresponding direction, set the correction parameter to 0.