Acceleration control device for a hydraulic drive unit

An acceleration control device for a material transfer apparatus such as a conveyor or the like, comprising:

• a hydraulic drive unit for imparting motion to the material transfer apparatus, said drive unit having a hydraulic fluid pump that provides power for moving the material transfer apparatus, the fluid output of said pump and thus the speed of the material transfer apparatus being determined by the position of a rotatable control shaft about its longitudinal axis between an off position corresponding to a low fluid output configuration of the pump and a stopped condition of the material transfer apparatus, and an on position corresponding to a high fluid output configuration of the pump and a moving condition of the material transfer apparatus, the change in the fluid output of the pump caused by rotation of said control shaft to positions between said off and on positions and thus the acceleration or deceleration of the material transfer apparatus being proportional to an arc length through which said control shaft is rotated;
• crank means connected to said control shaft for rotating said control shaft about its longitudinal axis between said off and on positions in response to rotation of said crank means about the longitudinal axis of said control shaft, the arc length through which said control shaft is rotated being proportional to the arc length through which said crank means is rotated;
• support means;
• motive means supported on said support means, said motive means having a movable element and being configured to move said element through a distance between a first position which corresponds to the off position of said control shaft and a second position which corresponds to the on position of said control shaft;
• actuation means for actuating said motive means to move said element between said first and second positions;
• a mechanical linkage connected between said movable element of said motive means and said crank means to impart rotational movement to said crank means in response to movement of said element, said linkage being configured together with said crank means so that movement of said element between its first and second positions causing rotational movement of said crank means causes said control shaft to be rotated between its off and on positions, respectively;
• and
• said mechanical linkage being further configured to provide a substantially nonlinear relationship between the distance through which said movable element is moved by said motive means and the arc length through which said crank means is rotated by said movable element over a given time interval such that the arc length through which said crank means is rotated is at a minimum in relation to the distance through which said movable element is moved when said element is immediately adjacent its first position and the arc length through which said crank means is rotated increases gradually in relation to the distance through which said movable element is moved as said element is moved away from its first position, whereby said nonlinear relationship is also established between said movable element and said control shaft so that moving said movable element through said distance causes said control shaft and thus the material transfer apparatus to accelerate and decelerate gradually to minimize disturbances of the conveyed material associated with starting and stopping movements.