Lens autofocus actuating device

1. A lens autofocus actuating device, comprises:

a base, which has an upper surface;

a guide rail unit, which is disposed on the upper surface of the base and comprises:

a fixing ring; and

a plurality of position limiting members, which are respectively stood on the fixing ring;

a lens carrier; which is disposed above the base and located between the position limiting members, wherein an outer side surface has a plurality of cavities and a disposing space is consisted of one of the cavities and the corresponding position limiting members;

an actuating member, which is disposed on the upper surface of the base and has two electrode terminal pairs and two shape-memory alloy wires disposed opposite to each other, wherein each shape-memory alloy wire is in contact with a corresponding protrusion of the lens carrier, and the two ends of each shape-memory alloy wire are respectively connected to the electrodes of each group of electrode terminal pairs, wherein the shape-memory alloy wires are driven by electric current to produce thermal deformation and then actuate the lens carrier to move relative to the base;

a plurality of balls, which are divided in a plurality groups, wherein each group of balls is positioned in the corresponding disposing space and in contact to the surface of the position limiting members and the cavities;

a shell, which is connected to the base to cover at least the guide rail unit, the lens carrier and the actuating member; and

two resilient members, which are disposed opposite to each other between an upper surface of the lens carrier and the shell, and provide a returning force to move the lens carrier toward the direction of the base after the shape-memory alloy wires are cooled.

2. The lens autofocus actuating device of claim 1 , wherein the position limiting members are uniformly disposed on the fixing ring.

3. The lens autofocus actuating device of claim 2 , wherein the included angle between each of position limiting members is 120 degrees.

4. The lens autofocus actuating device of claim 1 , wherein each position limiting member is L-shaped with the notch of L-shape faces the outer side surface of the lens carrier.

5. The lens autofocus actuating device of claim 1 , wherein the material of the fixing ring of the guide rail unit and the position limiting members is metal, plastic steel or plastic.

6. The lens autofocus actuating device of claim 1 , wherein the fixing ring of the guide rail unit is contacted with the position limiting members by welding joint, gluing of curing adhesive, high-temperature welding or laser welding.

7. The lens autofocus actuating device of claim 1 , wherein each of two electrode terminal pairs has two electrodes, one of the electrodes of the two electrode terminal pairs is electrically connected to each other.

8. The lens autofocus actuating device of claim 1 , further comprises:

a circuit board, which is disposed on a side of the lens carrier and is stood on the upper surface of the base, with a Hall sensing member electrically connected with it; and

a magnetic member, which is disposed facing the Hall sensing member in a cavity on the outer side of the lens carrier.

9. The lens autofocus actuating device of claim 1 , wherein the base further has a plurality group of positioning members, which are respectively disposed corresponding to each position limiting member on the upper surface of the base for the positioning of these position limiting members.

10. The lens autofocus actuating device of claim 1 , wherein the material of the balls is metal or precision ground ceramics.

11. The lens autofocus actuating device of claim 1 , wherein the number of resilient members is even.