A miniature pan-tilt actuator: the spherical pointing motor

TitleA miniature pan-tilt actuator: the spherical pointing motor
Publication TypeJournal Articles
Year of Publication1994
AuthorsBederson BB, Wallace RS, Schwartz EL
JournalIEEE Transactions on Robotics and Automation
Pagination298 - 308
Date Published1994/06//
ISBN Number1042-296X
Keywordsabsolute positioning device, active vision, Actuators, Application software, Assembly, automatic calibration, camera sensor, CAMERAS, CCD image sensors, CCD sensor chip, Charge coupled devices, Charge-coupled image sensors, closed-loop control strategies, computerised control, Lenses, Magnetic fields, miniature lens assembly, miniature pan-tilt actuator, open-loop control strategies, orthogonal motor windings, pan-tilt mechanism, Permanent magnet motors, position control, Scanning probe microscopy, spherical pointing motor, two-degree-of-freedom device

A pan-tilt mechanism is a computer-controlled actuator designed to point an object such as a camera sensor. For applications in active vision, a pan-tilt mechanism should be accurate, fast, small, inexpensive and have low power requirements. The authors have designed and constructed a new type of actuator meeting these requirements, which incorporates both pan and tilt into a single, two-degree-of-freedom device. The spherical pointing motor (SPM) consists of three orthogonal motor windings in a permanent magnetic field, configured to move a small camera mounted on a gimbal. It is an absolute positioning device and is run open-loop. The SPM is capable of panning and tilting a load of 15 grams, for example a CCD image sensor, at rotational velocities of several hundred degrees per second with a repeatability of .15°. The authors have also built a miniature camera consisting of a single CCD sensor chip and miniature lens assembly that fits on the rotor of this motor. In this paper, the authors discuss the theory of the SPM, which includes its basic electromagnetic principles, and derive the relationship between applied currents and resultant motor position. The authors present an automatic calibration procedure and discuss open- and closed-loop control strategies. Finally, the authors present the physical characteristics and results of their prototype