ISR research accomplishments

Vibratory Linear Motor Systems
US Patent 4,994,698    Feb. 19, 1991

Research team

Roger W. Brockett (Harvard/ISR)
Gerald B. Kliman (General Electric)
Donald W. Jones (General Electric)
Russell E. Tompkins (General Electric)

Accomplishment

The need for the systems. Mechanical rectification involves converting reciprocating motion to either rotational motion or rectilinear motion. The classic mechanical rectifier is a piston/crankshaft mechanism. To produce mechanical advantage in the classic system, gearing and lubrication are required, thus making such a system unsuitable for applications requiring both a compact mechanism and a high degree of precision, such as robotics applications, e.g. prostheses and other high force-to-weight ratio applications. Such a system is likewise unsuitable for applications involving high-temperature or vacuum environments. Recently, however, vibratory motors, which may be well-suited to such applications, have been considered theoretically.

Linear motors employing piezoelectric transducers rely on intermittent frictional contact between a rotor movable along a contacting surface and a vibrating stator, which is excited by piezoelectric elements, resulting in the propagation of a travelling wave along the contacting surface. The contacting surface of the motor follows an elliptic path which results in unidirectional motion.A different mode of operation is possible wherein piezoelectric transducers are employed directly as extenders and clamps to generate linear motion. Disadvantageously, since piezoelectric materials comprise the primary moving, or "working," elements of such motors, the power output capability is generally limited by the energy density and strain of piezoelectric materials.

What do the systems accomplish? This patented invention provides a new and improved linear motor that is simple in construction and is practical for applications involving a wide range of load levels. It employs electromagnetic excitation and control and provides a high force, low speed, vibratory linear motor suitable for use in robotics applications and applications involving extreme environments, i.e. high- temperature or vacuum environments.

The electromagnetic excitation means is used to induce transverse mechanical oscillations of a relatively thin, spring-like beam mounted between a pair of clamping means. The electromagnetic excitation means comprises a comb-shaped, or multi-poled, electromagnet disposed centrally with respect to the clamping means. The clamping means provide boundary conditions for a standing wave vibration established on the beam by the electromagnetic excitation means.

In operation, the clamping means are suitably controlled to produce linear motion of the beam in either a right-hand or left-hand direction, as desired, as the beam oscillates, hence converting oscillating, or reciprocating, motion to rectilinear motion. The clamping means comprise left-hand and right-hand electromagnetically actuated brakes which are normally held on, i.e. clamped to the beam, by a high force spring system.

Alternatives include magnetostrictive and piezoelectric brakes. Approximately rectangular current pulses are applied to the comb-shaped electromagnet and brake windings in such manner as to produce mechanical oscillations of the beam and to control the rectified linear motion thereof. Alternatively, a sine wave excitation may be provided to the comb-shaped electromagnet, while approximately rectangular current pulses are applied to the brake windings. The magnitudes, phases and waveforms of the signals used to excite the electromagnet and brakes may be controlled to achieve optimum operation.

For more information

View this patent at Delphion.