US Patent 7695213 Cam-lift for a manhole cover

A manhole cover assembly including a frame defining an opening and a cover sized to engage the opening. A lift pin is retained by the frame, defining a first axis, and includes a bearing portion, and a top end connected to the cover. The lift pin is free to slide axially along the first axis. A spiral cam is retained to the frame by a torque shaft including an upper and lower end, defining a second axis offset from the first axis. The spiral cam includes a cam surface in selective engagement with the bearing portion of the lift pin so that rotation of the torque shaft about the second axis causes rotation of the spiral cam about the second axis and displacement of the lift pin along the first axis.