Problem description.
The resonant magnetic actuator is often applied in power toothbrushes. This actuator has many advantages over a drivetrain consisting of a permanent-magnet motor with an eccentric. It is much easier to realize a silent, high-frequency driver with a longer lifespan. Furthermore, the resonant drive can be seen as a direct-drive system that operates close to the final load, thereby achieving high efficiency.
However, the problem is that the resonant actuator produces a stroke that is dependent on the load, while the motor with an eccentric provides a constant stroke. Various approaches could be considered to obtain a more stable stroke. One solution often sought is in the choice of the operating point: a driving frequency further from resonance increases stability but also leads to lower efficiency. A substantial technical solution involves adding a control loop. Stable and efficient designs become possible, but the drivetrain also becomes more costly due to the required stroke sensors.
Relevance
The central idea behind this assignment is to investigate a system in which the actuator also functions as a sensor. The instantaneous stroke is reconstructed from the actuator voltage and current using an algorithm. A measurement and control system is then proposed to stabilize the stroke.
Aimed output
- What will the student need to do?
- Examining a suitable stroke reconstruction algorithm. Because the nature of the actuator used is of great importance, the different actuator properties are mapped out.
- Testing the mentioned sensor function, both in simulations and in practice.
- Investigating sensor quality sensitivity due to variations in actuator properties.
- Designing a control loop that uses the sensor method to stabilize the stroke.
- Testing the controlled system, in simulation and in practice. Load variations must be considered.
- Writing a report in which all the findings are described.
- Main topics the student will work on
- Stroke quality and efficiency of the toothbrush drivetrain
- Efficient sampling techniques
- Non-linear resonant actuators
- Stable control loops for resonant drivetrain with a highly varying load
Initiator/Supervisor: P.J. Bax
Type of assignment: Graduation project
Desired duration: 6 months
Publication date: April 30th, 2026