Abstract: A controllable platform suspension system (20) for treadmills (18) and other platforms and devices therefor which exhibit controllability of the impact condition of the platform, such as a treadmill deck (36). In the treadmill application, user-selectable damping/stiffness is provided to simulate variable track conditions, such as pavement, rubber, grass, gravel, sand, and the like. The controllable suspension system (20) comprises spring mounts (40) or the like or a flexible deck (36) for allowing movement of the deck (36) relative to the frame (22) at a contact location (29) due to impact and a controllable device such as an Electrorheological (ER) device, Electrophoretic (EP) device, Electromechanical Hydraulic (Semi-Active) device, controllable mounting, or a Magnetorheological (MR) device, such as an MR brake (42a, 42a, 42b), MR damper (42d), or MR mount (42c, 42e, 42f) interconnecting between the frame (22) and platform (36) to provide the user-variable impact restraint.

Abstract: A controllable brake (20) including a rotor (28) supported by a shaft (30) which is rotatably supported by bushings (42) received in housing (22). A coil assembly (48) creates a magnetic field within a pole piece (32), which is preferably manufactured from a powdered metal material, which preferably has a density of between about 6.8 and 7.0 gm/cm. A magnetically-soft medium is contained within first and second gaps (86, 88) located between pole piece (32) and rotor (28). In one aspect, a magnetic saturation zone (25) reduces the propensity of magnetizing the shaft (30). In another, the pole halves (24, 26) are received in radially-spaced pole pockets (37) formed in the housing (22) and include an axial bias spring (70) to ensure intimate contact. In another aspect, a lip projection (76) traps fluid (23) between the lip projection (76) and shaft (30) and minimizes fluid exposure to the shaft seal (44). In another aspect, cooling fins (55) or a projection (53) restrains rotation of the housing (22).