An apparatus for raising and lowering a payload, particularly a chair and its user to provide assistance with the sit-to-stand task. The apparatus comprises a platform, a left lifter assembly, a right lifter assembly, means to power both lifter assemblies, and means to control the raising and lowering thereof. Means to sense and correct sideways tilt, desirable to preclude excessive tilt if one of the lifters fails, are described. The user may use an existing, favorite chair, including a reclining chair, which is placed upon the platform without modification. In a low position, the platform is very close to the floor, providing comfort during sitting. In a high position, the platform is greatly elevated, to provide a full measure of sit-to-stand assistance. The apparatus doesnt interfere with posterior foot placement during the sit-to-stand process, and doesnt interfere with reclining while sitting. The apparatus is easily deployable, movable, and storable.
