Abstract: The torque, due to the weight of the arm, is balanced according to the angular position of the arm by a contrast spring acting perpendicular to the axis of rotation of the arm. The spring is controlled by a cam integral with the arm, is housed in a container closed by a wall acted on by the profile of the cam, and rests on a guide disk whose position relative to the container is adjusted by means of an adjusting screw to calibrate the precompression of the spring according to the minimum torque due to the weight of the arm. In another embodiment, at least one contrast spring acts parallel to the axis of rotation of the arm, and is controlled by a cam edge of a cylinder for axially moving a corresponding sleeve housing the spring.

Abstract: The torque, due to the weight of the arm, (16, 17), is balanced according to the angular position of the arm by a contrast spring (29) acting perpendicular to the axis of rotation of the arm (16, 17). The spring (29) is controlled by a cam (34, 34?) integral with the arm (16, 17), is housed in a container (32) closed by a wall (31) acted on by the profile of the cam (34, 34?), and rests on a guide disk (33) hose position relative to the container (32) is adjusted by means of an adjusting screw (43) to calibrate the precompression of the spring (29) according to the minimum torque due to the weight of the arm (16, 17). In another embodiment, at least one contrast spring (66) acts parallel to the axis of rotation of the arm (16, 17), and is controlled by a cam edge (59) of a cylinder (56) for axially moving a corresponding sleeve (62) housing the spring (66).