Design and Analysis of a Novel Gravity-Compensating Vertical Linear Motor

We propose a vertical linear motor (VLM) for semiconductor manufacturing equipment that compensates for the weight of the moving part by using the balance of magnetic and elastic forces. The developed VLM achieves zero stiffness with a constant upward force over a working range. The magnetic circuit of the VLM is designed to provide a linear negative stiffness over a ±2 mm stroke, with an upward force of 14 N at a 0 mm stroke. The negative stiffness is compensated for by the positive stiffness of elastic component-like springs. The upward force is then constant over the working range and corresponds to the weight of the moving part. The proposed VLM is designed to minimize the coupling effects of stiffness and gravity compensation forces by using magnetic flux saturation and magnetic flux path design. We investigate the effects of each design parameter on VLM operation through finite element analysis. Finally, the simulated forces in the proposed VLM are experimentally verified, indicating a linear negative stiffness of approximately −13.5 N/mm and a gravity compensation force of 14.9 N