Human power amplifier for lifting load including apparatus for preventing slack in lifting cable

A human power amplifier assist device, including a pulley with line wound thereon, an actuator arranged to turn the pulley so as to raise and lower the line wound thereon, and an end-effector connected to the line wound on the pulley and connectable to a load, the end-effector including a handle to be held by an operator and a sensor detecting an operator-applied force on the handle, the assist device comprising:

• a. a controller controlling operation of the actuator, the controller being responsive to a first signal from the sensor representing operator-applied force and a second signal representing tensile force on the line;
• and
• b. the controller being programmed to cause the actuator to turn the pulley so as to raise and lower the line, and to halt the actuator so that the line and the end-effector connected thereto is maintained in a certain position, as a function of the first and second signals.