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Traditionally linear actuator applications are addressed by the use of hydraulic systems. The high maintenance cost and poor reliability will always be the most critical problem in the real applications. Benefited from both the high mechanical advantage of the roll screw and the simple structure of the switched reluctance motor, a new SRM driven linear actuator is proposed as a replacement for the traditional hydraulic system. The key factor is to improve drive system reliability without losing the high thrust/ high power density characteristic of the original system. Through the Landing Craft Air Cushion (LCAC) project example, the detail of the magnetic design is done step-by-step to maximize the SRM power density. The technique credibility is crosschecked by both the SRDaS software and the finite element method. For further improvement of system reliability, converter structure, sensorless control and fault tolerance ability are also investigated. Both the computer simulation and the experimental results verified the validity of the high thrust linear actuator design.
The Linear Induction Motor (LIM) is another type of low cost, low maintenance linear actuator for medium/high speed application. There are several constraints which should be considered during the LIM design procedure. The motor manufacturer needs to minimize the motor weight to save material and also limit the total supply current for thermal consideration. The drive designers are always looking for the maximum thrust with less supplied voltage. The wide operating speed requirement also makes the design decision more complex. In the research new asymmetric structure is proposed in the design, which can ideally double the design option from just even coil numbers per slot to the full integer range. The asymmetric structure has the potential to introduce a new balance point between the low-speed and high-speed performance of the LIM. Experimental results demonstrate the significant gain of the asymmetric motor compared with its symmetric counterpart. The airgap length is also found to be a key factor for the application in the experiments. |
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