Counterbalance robot arm

Counterbalanced robot apparatus, comprising a main arm having first and second substantially parallel main arm sections respectively having proximal and distal ends, shoulder trunion means supportingly connected to the first main arm section between the proximal and distal ends thereof, a forearm assembly having an elbow section with first and second pivots, the distal end of the first main arm section being connected to the first pivot, and the distal end of the second main arm section being connected to the second pivot, a drive arm having an outer end and an inner end, the inner end being connected by a first pivotal connection to the first main arm section near a proximal end thereof, a medial portion of the drive arm being connected by a second pivotal connection to the second main arm section near a proximal end thereof, drive motor means connected to the drive arm at an outer end remote from the first and second main arm sections, speed reducer drive means connected to the motor means, to the second main arm section and to the drive arm for changing the angular relationship between the drive arm and the second main arm section, and means, comprising the substantially parallel drive arm and forearm assembly and the substantially parallel main arm sections, for maintaining substantially equal opposite angles between the forearm assembly and at least one main arm section and between that one main arm section and the drive arm, wherein a line between the first pivot and the first pivotal connection is substantially parallel to a line between the second pivot and the second pivotal connection, whereby a line between the first and second pivots is substantially parallel to a line between the first and second pivotal connections, and whereby the four respective transverse axes of the pivots and the pivotal connections intersect the plane of the main arm at the apices of a parallelogram.