A rotatively restrained nut is fixedly connected through the agency of sleeve, plug and other components to a member which is to be reversibly driven axially, for example, a periodically reversed reciprocable ram or plunger, the nut and connected assembly being operated for the purpose by an elongated, axially fixed motor-driven screw. At an end of its stroke in one direction the nut bottoms against an impact washer and, through the latter, against a resilient cushioning stop pad. The stop surrounds the corresponding end of the rotary screw and is restrained from axial movement relative to the screw by a cupped retainer member, which also limits the extent of radial expansion of the pad under axial compression by the nut. As thus additionally loaded in torsion, at the instant of a resiliently cushioned engagement of the nut in thus bottoming and coming to an axial stop, the screw imposes an instantaneously increased load on the drive motor with the result that, through the agency of a sensitive device, a centrifugal reversing switch, a built-in limit switch means, or like conventional agency, the direction of rotation of the motor and screw is reversed. The nut assembly operated thereby commences travel in the opposite direction, aided in a cushioned start by resilient wind-up energy stored in the cushion at the time of engagement by the nut. Reaching the end of this reversed stroke, further axial travel of the nut is mechanically halted; and there results again an increase of torque load on the motor, due in this case to reactive tensile force exerted by the screw on the cushion to compress the latter in coming to a halt. The motor again is reversed, as assisted in a soft start by a torque wind-up effect at the cushion.
A manipulator having at least one jib which can be swivelled about a vertical shaft is disclosed. The vertical shaft is arranged on a support member. The jib may carry a positioning unit having load-holding members mounted thereon.
