Certain driving mechanisms for driving objects such as camera lenses need to be capable of accurately positioning the object in at least two dimensions, such as in the rotary and linear directions, during operation. Usually, the linear and angular positions of rotary-linear driving mechanism can be determined by optical means. For example, U.S. Pat. No. 6,765,195 entitled “Method and Apparatus for Two-Dimensional Absolute Optical Encoding” describes an optical encoder for determining the position of an object in two dimensions. The encoder comprises a scale having a pattern being predetermined to indicate an absolute location on the scale, means for illuminating the scale, means for forming an image of the pattern, detector means for outputting signals and analyzing means for determining the absolute location of the object in two directions. From the scale and pattern, the position of the object is known, and the driving mechanism may thus control the movement of the object in two dimensions.
However, optical encoders are generally bulky and expensive to use. In particular, much space is required for installing the encoder lens assembly as well as an optical scale to detect the position of the object. For a compact apparatus where installation space is at a premium, an optical encoder is not desirable.
Another type of encoder uses an inductance-type sensor which does not need optical means to detect the position of an object. An example of such an encoder is disclosed in U.S. Pat. No. 5,757,182 entitled “Variable-Reluctance-Type Angular Rotation Sensor with Sinusoidally Distributed Winding”. In this set-up, sinusoidally distributed windings are formed on uniformly-distributed slots such that the angular position of the driven object can be determined using variable-reluctance principles. However, such inductance sensors have conventionally not been able to detect the position of an object in two directions, such as both angular displacement as well as linear displacement. Accordingly, the driving mechanisms incorporating inductance-type position encoders are operative to provide controlled driving of an object only in one direction, specifically the rotary direction. It would be desirable to provide an inductance-type encoder that is more compact than an optical encoder and is able to detect the position of an object in two dimensions. Such a driving mechanism may provide controlled driving of an object in two dimensions, especially in applications which require the driving mechanism to move an object linearly as well as to rotate the object.
Moreover, present motors providing both rotary and linear motions require two sets of coils and magnets to provide the rotational torque and linear motion force. This also requires two drivers to drive the respective sets of coils and magnets, all of which increase component count and costs. For example, U.S. Pat. No. 7,038,334 entitled “High Precision Laser Machining Apparatus” describes how to use a rotary motor and a separate linear motor to provide rotary and linear motions respectively.