Exercise weight stacks are well known in the art and prevalent in the exercise equipment industry. Generally speaking, a plurality of weights or plates are arranged in a stack and maintained in alignment by guide members or rods. A desired amount of weight is engaged by selectively connecting a selector rod to the appropriate weight in the stack. The selector rod and/or the uppermost weight in the stack are/is connected to at least one force receiving member by means of a connector. The engaged weight is lifted up from the stack in response to movement of the force receiving member.
Some examples of weight stacks, their applications, and/or features are disclosed in U.S. Pat. No. 1,053,109 to Reach (shows a stack of weight plates, each having a slide which moves into and out of engagement with the weight plate or top plate above it); U.S. Pat. No. 3,912,261 to Lambert, Sr. (shows an exercise machine which provides weight stack resistance to a single exercise motion); U.S. Pat. No. 4,411,424 to Barnett (shows a dual-pronged pin which engages opposite sides of a selector rod); U.S. Pat. No. 4,546,971 to Raasoch (shows levers operable to remotely select a desired number of weights in a stack); U.S. Pat. No. 4,601,466 to Lais (shows bushings which are attached to weight stack plates to facilitate movement along conventional guide rods); U.S. Pat. No. 4,809,973 to Johns (shows telescoping safety shields which allow insertion of a selector pin but otherwise enclose the weight stack); U.S. Pat. No. 4,878,662 to Chern (shows a selector rod arrangement for clamping the selected weights together into a collective mass); U.S. Pat. No. 4,878,663 to Luquette (shows an exercise machine which has rigid linkage members interconnected between a weight stack and a force receiving member); U.S. Pat. No. 4,900,018 to Ish III, et al. (shows an exercise machine which provides weight stack resistance to a variety of exercise motions); U.S. Pat. No. 5,000,446 to Sarno (shows discrete selector pin configurations intended for use on discrete machines); U.S. Pat. No. 5,037,089 to Spagnuolo et al. (shows a controller operable to automatically adjust weight stack resistance); U.S. Pat. No. 5,263,915 to Habing (shows an exercise machine which uses a single weight stack to provide resistance to several different exercise motions); U.S. Pat. No. 5,306,221 to Itaru (shows a stack of weight plates, each having a lever which pivots into and out of engagement with a selector rod); U.S. Pat. No. 5,374,229 to Sencil (shows an alternative to conventional guide rods); and U.S. Pat. No. 6,186,927 to Krull (shows selector rods that rotate into engagement with weights within a stack), all of which are incorporated herein by reference. Despite these various advances in the exercise weight stack art, room for improvement and ongoing innovation remains.