Junichi Noma

Development of a Compact Magnetorheological Fluid Clutch for Human-Friendly Actuator

There is a strong demand for a human–machine-coexistent machine, e.g., a power-assist system or a computer-aided rehabilitation system, in the context of the super-aging society. In such a human–machine-coexistent system, it is important to guarantee hardware-level safety by utilizing human-friendly actuators. In this study, we have developed a compact magnetorheological fluid clutch (CMRFC) for human-friendly actuators. In this paper, at first, the basic design of the CMRFC and developments of 5- and 40-Nm class devices are explained. Then we discuss experimental results on the basic characteristics of these devices. In the final part, a new magnetorheological fluid that includes nano-sized particles is discussed.

Response time of magnetorheological fluid–based haptic device:

Haptics is a tactile feedback technology that recreates the sense of touch to the user by applying forces, vibrations, or motions. Haptic devices should have a high performance in their output characteristics, for example, low friction in off-state, constant force with constant input, and quick response with dynamic input, in order to generate a sufficient sense of touch to human skin. We have focused on rapid response of magnetorheological fluid and decided to use it as the working material of the haptic device. There are several types of magnetorheological fluids available, and the effects of the different types of magnetorheological fluids on the response time of the haptic device have not yet been reported. The objective of this study is to experimentally investigate the response time of a magnetorheological fluid–based haptic device with two different types of magnetorheological fluids. We originally developed a single-disc type magnetorheological fluid–based haptic device, and its response time was investigated with two types of magnetorheological fluids. We set three experimental conditions with regard to the fluid gap and rotational velocity. We modeled the haptic devices as a classic first-order lag system, and the time constant of this system was assumed to be representative of the response time of the haptic device. According to the results, the response times of a sample tend to be smaller with the narrow gap (0.1 mm), whereas those of the other tend to be smaller with the large gap (0.5 mm). In addition, the response time is non-dimensioned and investigated with Mason number.

Torque-controllable device using a magnetorheological fluid with nano-sized iron particles for a haptic device

Magnetorheological fluids (MRFs) include suspensions of ferromagnetic particles, medium oils, and several types of additives. Their rheological properties change rapidly, stably, and repeatedly when magnetic fields are applied. In this present study, we focus on a haptic device using MRFs. Though particle sedimentation is one of the drawbacks of MRFs, we developed an MRF using iron particles of size 10–100 µm and silicon oil (Nano-MRF); more specifically, we use this material as a working material for the haptic device. We developed a prototype of an MRF brake as a core device for haptic control. In this paper, we describe our design method for the corresponding magnetic circuit. In addition, we designed a detailed structure for the unit. We investigated the basic properties of this unit by using a test machine with two types of MRFs, i.e., our Nano-MRF and a commercial MRF. From our results, the Nano-MRF showed better stability and response times versus that of conventional materials.