Magnetorheological fluid devices: an advanced solution for an active control on the wood manufacturing process

A detailed analysis of the behavior of a commercial magneto-rheological device is presented in the context of woodworking machine tools. This type of device can provide resistive torque to a rotating shaft via a change in fluid viscosity due to a modification in magnetic field, with the resistive torque being proportional to the current passing through an electric winding inside the device. In this way, it is possible to control the transmission of torque by modulating an electrical current. This solution is particularly relevant where highly accuracy torque control is required. At the same time, it is recognized that magneto-rheological devices can introduce a significant delay between activation of the control signal and application of torque. As a consequence, it is necessary to analyze the behavior of the clutch by direct evaluation. Several tests have been performed while increasing the current and experimentally evaluating the applied torque and hysteresis behavior. The presented results demonstrate the need to use software algorithms to fill the time gap between the expected and measured torque and to overcome difficulties related to hysteresis before such a clutch can be implemented for high accuracy applications.