Glideforce MD122004-P Medium-Duty Linear Actuator with Feedback:

This 12 V medium-duty (MD) linear actuator can lift loads up to 100 kgf [225 lbs or 1000 N] and can withstand static loads up to 450 kgf [1000 lbs or 4500 N]. It has a maximum speed of 14.7 mm/s [0.58"/s] at no load and 10.4 mm/s [0.41"/s] at the maximum load. Limit switches at each end make the actuator easy to control over its full range of motion. The shaft holds its position when unpowered. This version has a 4-inch stroke (3.9" usable) and a feedback potentiometer that lets you determine where the actuator is in its stroke.