Lens module, projection device, and focusing method of projection device

A lens module, adaptable for a projection device, wherein the lens module comprises:

• a projection lens, a rotary adjustment member, a gravity sensor, a drive module, and a controller, wherein:
• the rotary adjustment member is connected to the projection lens and is adapted to be rotated to adjust a focal length of the projection lens;
• the gravity sensor is disposed on the rotary adjustment member, is adapted to rotate synchronously with the rotary adjustment member, and is configured to provide a sensing signal corresponding to the rotary adjustment member;
• the controller is electrically connected to the drive module and the gravity sensor and is configured to control the drive module and receive the sensing signal from the gravity sensor;
• and
• the drive module is connected to the rotary adjustment member and is adapted to drive the rotary adjustment member to rotate under a control of the controller;
• wherein the controller calculates a rotary angle value of the gravity sensor according to the sensing signal of the gravity sensor, and the rotary angle value comprises a first rotary angle value and a second rotary angle value;
• the controller is configured to:
• control the drive module to drive the rotary adjustment member to rotate in a first direction, so that the gravity sensor rotates with the rotary adjustment member from a starting position and stops at a first position;
• receive the sensing signal of the gravity sensor which is rotated from the starting position to the first position to obtain the first rotary angle value;
• control the drive module to drive the rotary adjustment member to rotate in a second direction, so that the gravity sensor rotates with the rotary adjustment member from the first position and stops at a second position, wherein the first direction is opposite to the second direction;
• receive the sensing signal of the gravity sensor which is rotated from the first position to the second position to obtain the second rotary angle value;
• obtain a maximum rotary range of the rotary adjustment member according to the first rotary angle value and the second rotary angle value, and obtain a time required for the gravity sensor to rotate for a preset angle value when the drive module drives the rotary adjustment member;
• and
• adjust the focal length of the projection lens according to the maximum rotary range and the time required for the gravity sensor to rotate for the preset angle value.