This research focuses on development of 3-DOF haptic master manipulator featuring Magneto-rheological brakes (MRBs) and a mechanism of spherical manipulator. The haptic manipulator is composed of a spherical manipulating mechanism integrated with 3 MR brakes. The first MRB is a rotary disc-type MRB employed at the waist joint to feedback the tangent force in the horizontal plane, the second MRB is also a rotary disc-type MRB employed at the shoulder joint to feedback the tangent force in the elevation plane, and the third MRB is a linear MRB employed at the prismatic joint to feedback the normal force (approach force). Position of the manipulator’s end-effector is measured by two rotary encoders and an LVDT. After the introduction, a configuration and working principle of the 3-DOF haptic spherical manipulator are presented. Mathematical models of the manipulator are then derived. The MRBs are then optimally designed to provide a required force feedback to the operator. A prototype haptic manipulator is then manufactured and its performance characteristics are then experimentally investigated.
This research focuses on development a speed control system of a rotary load shaft with different loading torque by using a clutch featuring magneto-rheological fluid (MRC). Firstly, a new configuration of a speed control system using MRC is proposed. Modeling of the MRC based speed control system is then derived based on Bingham plastic model of magneto-rheological fluid (MRF). Based on the derived model, an optimal design problem for the system is built and the optimal solution is obtained based on finite element analysis. Performance characteristics of the MRC based speed control system are then experimentally investigated. After that, the MRC based speed control system to control a varying rotary load shaft driven by an AC motor is proposed and a PID controller to control the speed is designed and implemented. Experiments on steady speed control of the rotary load shaft is then obtained and presented with remark discussions.
In this research, a high compact configuration of brake featuring MR fluid (MRB) is proposed. The proposed MRB consists of a rotor with multiple trapezoidal teeth acting at multiple magnetic poles of the brake. Two counter coils are placed on each side-housing of the brake. The inner face of each side-housing also has trapezoidal shape mating with the trapezoidal teeth of the rotor via MRF layer. By applying counter currents to the two coils, a magnetic fluid is generated with magnetic flux going across the MRF layer (MRF duct) between the rotor teeth and their mating poles on the housing. By using multiple poles with trapezoidal shape, a high braking torque of the brake is expected while the size of the brake is still kept to be compacted.
After a review of MRB state of the art, configuration of the proposed MRB is presented. The modeling of the actuator is then derived based on Bingham rheological model of MRF and magnetic finite element analysis (FEA). The optimal design of the MRB is then performed in order to minimize the mass of the MRB when braking torque is constrained to be greater than a required value. From the optimal design result, performance characteristics of the actuator is simulated and compared with previously developed MRB.
In industry, the AC motor is widely used because of low price, power availability, low cost maintenance. The main disadvantages of AC motors compared to DC motors are difficulty in speed and torque control, requiring expensive controllers with complex control algorithms. This is the basic limitations in the widespread adoption of AC motor systems for industrial automation. One feasible solution for AC motor control is using MRF (magneto-rheological fluid) based clutches (shortly called MR clutches) Although there have been many studies on MR clutches, most of these clutches used traditional configuration with coils wound on the middle cylindrical part and a compotator is used to supply power to the coils. Therefore, this type of MR clutches possesses many disadvantages such as high friction and unstable applied current due to commutator, complex structure which causes difficulty in manufacture, assembly, and maintenance. In addition, the bottleneck problem of magnetic field is also a challenging issue. In this research, we will develop a new type of MR clutches that overcomes the abovementioned disadvantages of traditional MR clutches and more suitable for application in controlling of AC motor. Besides, in this study, speed and torque control system for AC motors using developed MR clutches is designed and experimental validated.
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