Steering system for patient transfer device
A table assembly for a patient transfer device has an upper table with side plates that are differentially extended at the ends, and valve control for pneumatic tubing integrated with retraction of the side plates. During patient delivery only the delivery side plate is raised, to avoid catching linens in the nip formed between upper and lower belts. A slide assembly supporting the table assembly includes a fixed plate, an intermediate plate, and a full-motion plate which extend by means of rack-and-pinion drives. Each plate is symmetrical, and pinions are symmetrically located on opposite sides of the fixed or intermediate plate to allow hyperextension to either the left or right. Improved steerage for the device is provided by two centerline wheels which counter-rotate from a straight position to a turning position and further to a lateral position wherein the wheels are orthogonal to the longitudinal centerline of the device.
1. A steering mechanism for a transfer device, comprising:
a horizontal chassis;
a plurality of casters attached to said chassis defining a floor plane;
two wheels located along a longitudinal centerline of said chassis, generally symmetrically opposite a transverse centerline of said chassis;
means for counter-rotating said wheels about vertical axes in synchronized motion to at least three positions including a straight position, a turning position and a lateral position, wherein
said wheels are generally aligned with each other and with the longitudinal centerline of said chassis in the straight position,
said wheels are counter-rotated from the straight position by an acute angle in the turning position, and
said wheels are generally orthogonal to the longitudinal centerline of the chassis in the lateral position; and
means for raising said wheels above the floor plane in a stow position to allow the transfer device to be freely steered in any direction, said raising means including
a first bracket which rotates about one of the vertical axes,
a second bracket supporting one of said wheels which is pivotally attached to said first bracket to pivot in a vertical plane,
a cam follower attached to an upper edge of said second bracket, and
a stationary cam plate which gradually engages said cam follower as said first bracket rotates.
2. The steering mechanism of claim 1 wherein said wheels are impelled by respective motors which are independently energized with selected polarities to propel the transfer device when said wheels are in the straight position, the turning position or the lateral position.