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A new magnetorheological piston head design inspired by toroidal electromagnets was proposed in previous work as an alternative to conventional annular dampers. A prototype with a circular valve array integrated inside the piston head was built and tested to measure its passive performance. The mechanical, electromagnetic, and hydraulic models used in the new design were explained, and the relevant parameters of the actuator were analyzed to construct a mathematical model to estimate its performance. These works showed the feasibility of the concept and its potential as an alternative to current damper technology, but lacked a baseline for comparison. This paper reviews and widens this groundwork. It adds a magnetic finite element method study to address the previously found leakage, and a new set of experiments, including a force controller, to compare its performance against a conventional annular piston head. The new findings show how the current force limitations can be overcome by striking a balance between the coil space and the size of electromagnet cores to achieve the performance of current dampers. They also highlight its potential in force control applications to provide a wider range of customization options, such as number and size of holes, electromagnets, and coils, and a better use of the active area of the gap.

Compliant actuation is an indispensable element for safe physical human robot interaction. However, there is a lack of devices, which can integrate the high power density of hydraulic actuators with intrinsically safe mechanisms. This drove the development a new type of hydraulic magneto-rheological piston. This device includes a novel toroidal array of magnetorheological valves in its head. In previous studies, the system performance was evaluated only as a traditional damping system. Now, the piston is connected to a pump to create a hydraulic compliant actuator. This novel compliant piston is capable to control the piston speed and force independently by using the pump and electromagnet voltages respectively. In this way, different combinations of these parameters can be used to achieve diverse system properties; e.g. low response time or energy efficiency. Several experiments are conducted to evaluate its performance, including force, friction, speed, and step response. The results display the potential of the devices to be used as an active system for compliant hydraulic robotic applications. They also hint to the possibilities to improve by using a more sophisticated control system for its speed and force.

The advantages of mechanical compliance have driven the development of devices using new smart materials. A new kind of magnetorheological piston based on a toroidal array of magnetorheological valves, has been previously tested to prove its feasibility. However, being an initial prototype its potential was still limited by its complex design, and low output force. This study presents the revisions done to the design with several improvements targeting key performance parameters. An improved annular piston design is also introduced as comparison with conventional devices. The toroidal and annular piston head prototypes are built and tested, and their force performance compared with the previous iteration. The experimental results show an overall performance improvement of the toroidal assembly. However, the force model used in the study still fails to accurately predict the magnetic flux at the gaps of the piston head. This deviation is later verify and corrected using a FEM analysis. The force performance of the new toroidal assembly is on par with the commonplace annular design. It also displays a more linear behaviour, at the expense of lower energy efficiency. Finally, it also shows potential for a greater degree of customisation to meet different system requirements.

This work focuses on the analysis of the performance parameters of a new magneto-rheological device. Previously, a mathematical model of the actuator head was introduced; however, the complex relations between its parameters made its optimisation challenging, causing the device not to reach its full potential. In this work, the previous model is updated to fit a revised version of the toroidal design, as well as an annular design for comparison. The relations between different parameters are studied to find their trade-offs, and understand how they affect the performance of the actuators. Finally, an optimisation based on an iterative search for valid permutations of parameters, is used to find optimal combinations. Two prototypes are built and tested to validate the results of the optimisation. The study revealed the critical parameters of each design, which mostly depend on the relations between the magnetic flux density, and the active area exposed to the MRF; and successfully optimised the performance of the devices. However, work needs to be done to create a more complete tool with concrete guidelines for specific applications.

Interaction between humans and robots is expected to increase in the coming years. In order to ensure safety for the robot, its environment, and the people around it, it is necessary to have robust compliance actuation. Mechanically compliant devices such as magnetorheological actuators can ensure a high degree of safety through their intrinsic properties. This paper presents the modelling of a new kind of magnetorheological piston intended for linear actuation. An analysis using the reluctance method and an approximation of the Buckingham Reiner equation are used to develop the electromagnetic and hydraulic equations respectively, and key parameters of the system are presented. A simulation is done to evaluate the theoretical performance of the new piston design, its results are compared and validated by the experimental data obtained from a prototype. The simulation results show the capacity of the device for compliant actuation.

A new design of a magnetorheological piston prototype intended for passive or active force control in robotic applications for human robot interaction is introduced. It is based in a novel toroidal array of valves, contained within the piston head, which are used to control the output force of the actuator in order to achieve a high degree of reliability, size efficiency, and safety, by exploiting the material properties of magnetorheological fluids and permalloy metals. This paper describes the main points in the development of the magnetorheological piston prototype, the mathematical modelling of the magnetic circuit, and the results of the experiments conducted using a universal testing machine to evaluate the passive performance of the prototype. Results show the feasibility and performance of the new toroidal magnetic circuit of the magnetorheological hydraulic piston prototype. Improvements in order to be able to test the active performance of the design together with a pump setup are proposed.