<p>In this paper, a novel vertical linear actuator with gravity compensation is developed. The developed actuator generates the force that is equivalent to a payload without external current. It has advantages over a traditional linear actuator in terms of joule heat, thermal expansion, and the capacity of the actuator since it does not have to generate the force against the payload. There are several studies and patents about the gravity compensation linear actuators, especially in the field of semiconductor equipment. Some achieved the gravity compensation by combining the positive stiffness of an elastic component and the negative stiffness of electromagnetic force. If the stiffnesses are matched, the resultant stiffness becomes zero and the resultant force maintain a constant magnitude over a stroke. The other achieved it by designing the structure of the actuator, which had a complex structure.</p><p>Here, we designed a linear actuator with a simple structure that generated a constant force over the desired stroke by modifying the shape of the armature and the location of the permanent magnets. Additionally, the effects of the shape and size of the armature and the size and the location of the permanent magnets on the magnitude, the range, and the constancy of the gravity compensation force were analyzed using finite element analysis (ANSYS). The actuator consists of two permanent magnets, one ferromagnetic armature, and a stator. A coil is wound on the armature. Each permanent magnet interacts with the armature and generates an attracting force. The armature was designed to maintain the sum of the two electromagnetic forces by the two permanent magnets over the stroke of 4 mm. The input parameters related to the size and the location of the armature and the permanent magnets were selected. The forces were simulated over the stroke at the interval of 1 mm with each set of input parameters. The relations between the input parameters and the constancy over the stroke and the magnitude of the force were investigated. Finally, a model with one set of input parameters was fabricated and the simulation results were verified by experiment.</p>

Analysis and Design of a Vertical Linear Actuator With Gravity Compensation for Wafer Metrology Application

Paper Proceedings: https://asmedigitalcollection.asme.org/ISPS/ISPS2021/volume/84799

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