Method and apparatus for counterbalancing rotating bodies

Abstract

A diagnostic imaging scanner system is provided which includes an arm structure mounted to a support structure for pivotal motion about a substantially horizontal arm axis. A source of radiation directs radiation along a beam path. A detector is mounted on the arm structure in alignment with the beam path and is spaced from the source to accommodate placement of a subject under examination therebetween. During pivotal motion the detector thus moves along an arcuate path which lies in a substantially vertical plane. Means are provided for compensating the gravitational torque experienced about the arm axis during scanning motion. The compensating means includes means for producing a predetermined force and a cam mounted for pivotal motion about a substantially horizontal cam axis which is operatively coupled to the force means for converting the predetermined force to a first torque about the cam axis. Means are provided for rotatively coupling the cam to the arm strucure such that the first torque is transferred to a second torque about said arm axis. The second torque is substantially equal and opposite to the gravitational torque about the arm axis during scanning motion. The predetermined force means can include either a spring or a weight suspended against gravity. The cam defines a profile having a monotonically varying radius about its operative extent. The cam radius varies sinusoidally over its operative extent. Additionally, the cam profile may be further modified to take into account variations in the spring constant over the range of spring operation.