Linear actuator module based on multiple drives

Although hydraulic cylinders offer certain advantages, such as high force density and easy bolt-on mechanical assembly, they also have limitations like unclean operation, high maintenance requirement and difficulty of controls. This paper presents a competing drive concept that sidesteps these problems and achieves a high force-to-weight ratio by utilizing direct drives in a parallel arrangement. The proposed module allows high acceleration and high precision controls, while avoiding the self-locking problem associated with geared drives. First, a general overview of the actuator module is provided, which includes the electrical drive, the guideway system, measurement devices, and an optionally integrated power converter. The possible solutions applying different linear drive principles are evaluated and compared. In particular, the influence of iron-core and ironless direct drives on the force-to-weight ratio are analyzed. To achieve scalability in force, a modular design is adopted. In order to reduce the weight of the module, magnetic flux simulations are conducted that enable a substantial reduction in the backflow iron required for the drives arranged in parallel. The manufacturing of the coils and the assembly of the magnetic guideway are also discussed; in particular from the point of view of dealing with difficulties caused by statistical disparities in the magnetization properties among permanent magnets from the same batch. Finally, experimental results from the completed actuator are presented, including static and dynamic mechanical measurements and thermal behavior.