Adjustable computer keyboard support mechanism

An adjustable platform support assembly for attachment of a platform to a work surface, comprising in combination:

• a platform;
• a mounting member for attachment to the underside of a work surface;
• a support arm having a first end and a second end, said first end pivotally affixed to the mounting member for movement about a first substantially horizontal pivot axis and said second end pivotally affixed to a platform mounting assembly attached to the platform for movement about a second substantially horizontal pivot axis which is substantially parallel to the first horizontal pivot axis;
• means for locking the support arm to prevent pivotal movement about the first horizontal pivot axis;
• compensating means associated with the support arm for maintaining the orientation of the platform as the support arm assembly pivots about the first horizontal axis, said compensating means including
• a fixed sprocket mounted on the mounting member;
• a rotating sprocket at the second end of the support arm assembly mounted to the platform;
• a compensating belt operatively engaging both the fixed sprocket and the rotating sprocket, whereby when the support arm assembly is pivoted about the first horizontal axis the compensating belt wraps around the fixed sprocket and causes the rotating sprocket to rotate and maintain the orientation of the platform with respect to horizontal.