This invention relates to a shock absorber device for linearly decelerating a machine part by imposing a relatively constant force on the part over the stroke of the device.
Shock absorbers which force fluid through a restricted orifice to convert the kinetic energy of a moving part into an increase in the thermal energy of the fluid are commonly used on machines. The smoothest deceleration of the moving part is obtained by absorbers which offer a constant resistive force to the motion over the total duration of the deceleration.
In a typical installation, a machine tool or transfer arm is repetitively moving back and forth between separate operating positions and the movement of the tool or arm as it arrives at each position is cushioned and decelerated by a shock absorber positioned on the tool or arm or on the adjacent supporting structure. Ideally, as the tool or arm is decelerated at each end of its reciprocal movement, the shock absorber acts to exert a constant resistive force against the tool and smoothly decelerates the tool to a stop position in which the piston of the shock absorber has traversed substantially the entire length of the cylinder of the shock absorber so as to take advantage of the entire range of the fluid orifice means typically provided along the cylinder, and the piston comes to a stop just shy of the end of the cylinder so as to avoid destructive bottoming of the piston against the end of the cylinder. Since it is difficult to obtain these ideal deceleration conditions, and since it is further desirable to provide a positive delimiting means to establish the extent of movement of the tool or arm in each direction of reciprocal movement, it is common practice to employ a stop member at each end of the movement of the tool or arm against which the tool or arm comes to rest as the tool arrives at the end of its movement. Ideally positioned, the stops provide proper end limit positions for the tool or arm, avoid bottoming of the piston against the end of the cylinder to preclude damage to the shock absorber, and precisely position the piston end face with respect to the metering orifices adjacent the end of the stroke so as to provide proper deceleration at the end of the stroke. Although the shock absorber manufacturer commonly provids instructions for proper installation of the stop members at each installation site, it is not unusual that the stop members are not properly positioned with respect to the machine tool or transfer arm with the result that the proper end limit positions for the transfer arm are not established, or the piston bottoms against the end wall of the cylinder with consequent damage to the shock absorber, or the end face of the piston ends up in a position within the cylinder such that the proper deceleration is not provided at the end of the stroke.