Cross band coupling for stepper-motor-driven, rigid magnetic disc

Claim 1

In memory apparatus including at least one spinable and non-flexible magnetic disc, said apparatus supported by a base and intended for use in a digital computer system, rotary means for accurately positioning magnetic heads relative to tracks on at least one surface of said disc, said rotary means comprising: pivotable means, pivotably mounted on said base with pivot axis of said pivotable means substantially parallel to spin axis of said spinable magnetic disc, for supporting said magnetic heads; stepper motor means, including a rotational stepper motor mounted on said base with rotation axis of the shaft of said rotational stepper motor substantially parallel to said spin axis, for receiving electrical signals from said computer system and for step-rotating said shaft in response to said signals; taut-biased and flexible band means substantially inelastic in the taut-biased directions for coupling rotational motion of said shaft to said pivotable means in a manner to cause hysteresis free motion of said pivotable means about said pivotable axis whereby said magnetic heads are positioned along said disc surface; said pivotable means comprising a pivotable arm with said pivot axis near one end thereof and having means for interacting with said coupling means at the other end thereof, and a carriage arm cantilevered from said pivotable arm for holding said magnetic heads adjacent thereto; said stepper motor means further including pulley means, including a pulley fixedly mounted around said shaft and rotatable therewith, said pulley being formed from a circular disc-shaped member through which said shaft protrudes and from a circular wall having an aperture, said wall being connected at the periphery of said circular member and orthogonal to the plane of said member, for connecting to said band means; said pulley means including a coil spring contained within said wall and encircling said shaft, one end of said spring being fixed to said pulley and the other end protruding unconstrained through said aperture; and said band means comprising two separate crossed metal bands, both being connected near one of their respective ends at non-adjacent connecting points on said interacting means, one of said bands being connected near its other end to the outside surface of said wall and the other of said bands being connected near its other end to the protruding end of said spring, the bias on said spring being so oriented that it imposes a taut condition on said other of said bands which in cooperation with said interacting means and said wall imposes a taut condition on said one of said bands.