Direct drive for dental/medical hand pieces and micro-machining

18. July 2016

To machine very small work pieces (micro-machining) or for ergonomic reasons in dental and medical drills, the head of the machining spindle or the hand piece has a limited size. The electrical motor is only allowed to grow in one lateral direction if a direct drive is used.

In the dental drill example, the state-of-the-art is a low-speed motor (typically 40,000 rpm) with a mechanical connection to the hand piece driving the drill at the tool head through several mechanical transmission stages, see Figure 1 (left). The mechanical transmission stages introduce additional weight, acoustic noise and losses. A direct drive removes the need of the mechanical transmission; however, the space in the tool head is too small for a conventional machine that can generate the desired torque. In such a case, a lateral-stator machine (LSM) can be used (Figure 1 (right)) as it makes use of the space at the tool neck, which would otherwise not be used. Table 1 gives a comparison between the two solutions.

Comparison

Figure 1: Comparison between conventional and LSM solution

Based on the novel LSM concept, a prototype motor has been designed and realized with a maximal torque capability of 9 mNm and maximal speed of 200,000 rpm. A possible torque-speed characteristic is depicted in Figure 2. The prototype LSM dimensions is given in Figure 3, and a photo of the hardware is shown in Figure 4. There are different types of motors (Figure 5) and different rotor configurations (Figure 6) available. Sensor-based or sensorless operation options are available.

Torque and speed head curve

Figure 2: Torque and speed head curve of LSM

Dimensionen

Figure 3: Dimension of prototype LSM

LSM Prototyp

Figure 4: Prototype LSM

Different LSM types

Figure 5: Different LSM types

Different rotor configurations

Figure 6: Different rotor configurations

 

A LSM demonstrator, which has been developed together with the Power Electronic Systems Laboratory (PES) of ETH Zurich, is now available at Celeroton, and integration into your application is possible with adapted designs. We look forward to you contacting us (infocelerotoncom or phone +41 44 250 52 20) in order to check if the LSM can bring major advantages to your application. 

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