Head-up display device

1. A head-up display device installed in a vehicle, comprising:

a projector that projects a display light image representing vehicle-related information related to the vehicle;

an optical unit that includes a drivable reflecting mirror, which reflects the display light image projected by the projector, and that adjusts a virtual image display position, where a virtual image of the display light image reflected by the reflecting mirror is displayed, by drive of the reflecting mirror;

a stepping motor that rotates to drive the reflecting mirror;

a reduction gear mechanism that rotatably includes a plurality of transmission gears, which decelerate the rotation of the stepping motor and transmit the rotation to the reflecting mirror;

a resilient member that generates a restoring force in a direction that the plurality of transmission gears are engaged with each other; and

a control unit that controls a rotational position of the stepping motor in accordance with an adjustment command by an occupant of the vehicle, wherein:

at least one of the plurality of transmission gears that is predicted to incur a creep deformation is defined as a specific gear;

an environmental temperature of the specific gear, at which the specific gear is predicted to incur the creep deformation, is defined as a predicted deformation temperature;

a deviation predicted to be caused at the virtual image display position by the creep deformation at the predicted deformation temperature is defined as a predicted display deviation; and

the control unit corrects the rotational position in a direction to reduce the predicted display deviation when the environmental temperature rises to the predicted deformation temperature or higher.

2. The head-up display device according to claim 1 , wherein the control unit includes:

a correction execution block that executes the correction of the rotational position by a correction amount, which shifts the rotational position in the direction to reduce the predicted display deviation, when the environmental temperature rises to the predicted deformation temperature or higher; and

a post-correction control block that controls the rotational position in accordance with the adjustment command, with the rotational position corrected by the correction execution block used as a reference.

3. The head-up display device according to claim 2 , wherein the correction execution block executes the correction of the rotational position by the correction amount, which is variable based on a temperature correlation between the environmental temperature equal to or higher than the predicted deformation temperature and the predicted display deviation.

4. The head-up display device according to claim 3 , wherein:

the correction execution block executes the correction of the rotational position by the correction amount, which is one of a plurality of correction amounts having different values respectively corresponding to a plurality of temperature ranges equal to or higher than the predicted deformation temperature based on the temperature correlation; and

the one of the plurality of correction amounts corresponds to one of the plurality of temperature ranges to which the environmental temperature belongs.

5. The head-up display device according to claim 1 , wherein the control unit executes the correction of the rotational position when the environmental temperature rises to the predicted deformation temperature or higher for the first time after the head-up display device is installed in the vehicle.

6. The head-up display device according to claim 1 , wherein the control unit executes the correction of the rotational position when the environmental temperature in the vehicle rises to the predicted deformation temperature or higher after the vehicle stops.

7. The head-up display device according to claim 1 , further comprising a temperature sensor that detects the environmental temperature, wherein:

the reduction gear mechanism includes a casing that accommodates therein the temperature sensor together with the specific gear; and

the control unit executes the correction of the rotational position when the environmental temperature detected by the temperature sensor rises to the predicted deformation temperature or higher.

8. The head-up display device according to claim 1 , wherein at least a tooth-shaped portion of the specific gear is formed from resin.