Patent ID: 7785220

Claim:
A drive unit, comprising: a guide channel including a first journal housing and a second journal housing spaced a distance from the first journal housing to define an axis, the first journal housing having a generally C-shaped clamp with a gap and a threaded fastener engaging the C-shaped clamp on opposite sides of the gap, the second journal housing being a closed journal housing that is smaller than the first journal housing; an attachment assembly moveably attached to the guide channel; a flexible drive member attached to the attachment assembly and formed in a loop for moving the attachment assembly in the guide channel, characterized in that: a first pulley and a second pulley each being secured to the flexible drive member wherein rotation of either the first or second pulley will cause the attachment assembly to move in the guide channel; and an adjustable pulley assembly for rotatably mounting either the first pulley or the second pulley, the adjustable pulley assembly comprising a cam shaft with a first bearing portion, a second bearing portion concentric with the first bearing portion, and a cam surface located between the first bearing portion and the second bearing portion, wherein the cam surface rotatably supports either the first pulley or the second pulley, the first bearing portion and the second bearing portion being rotatably mounted to the adjustable pulley assembly about a fixed axis and the cam surface has an axis offset from the fixed axis such that rotational movement of the cam shaft will relocate the axis of the cam surface and relocation of the axis of the cam surface adjusts a tension in the flexible drive member.