John Makin

The Electro-Rheological Clutch: Design, Performance Characteristics and Operation

Fluid power transmission based on the electro-rheological clutch is taken beyond the concept-proving stage. A typical electro-rheological fluid is characterized over a range of engineering conditions and is found to usefully approximate to a continuum of Bingham plastic form. The clutch is optimized from this standpoint, and the limits of its performance are estimated. The state of the art is discussed alongside an outline of the infrastructure required to achieve maximum potential.

Dynamic simulation and performance of an electro-rheological clutch based reciprocating mechanism

A reciprocating mechanism which utilizes two electro-rheological clutches is described. An industrial application of the mechanism is in winding filaments onto bobbins. The required traverse speed is 5 m s-1 with a turn-round period of 10-20 ms, the traverse length is 250 mm and the turn-round position must be electronically controllable and repeatable within the ±1 mm. These combined criteria of high-speed and controllability makes the use of electro-rheological fluids an attractive proposition. The operation of the reciprocating mechanism and the dynamic model used to simulate the performance are outlined. The simulation is verified by comparison with experimental results from a prototype mechanism. Simulations are made to illustrate the effect of various fundamental electro-rheological fluid characteristics, such as electro-shear stress, time delays and viscosity. These simulations are considered in relation to the requirements for the operation of the high-speed mechanism.

Fluid Durability in a High Speed Electro-Rheological Clutch

The durability of an electro-rheological (ER) fluid was investigated by running a high speed ER clutch under different conditions and periods of operation. The tests involved running the clutch at 3000 rpm for a total period of twelve hours over a five day period. The tests subjected the fluid to a centripetal acceleration of 3000 m/s2, and were conducted with and without an excitation field of 2 kV/mm, and with and without shearing the fluid at shear rates up to 9500 s-1. The condition of the fluid was assessed periodically by measuring the torque response of the clutch to a step ap plication of voltage in respect of both magnitude and speed of response. Results at the two pole 50 Hz synchronous speed of 3000 rpm indicated that the particles in the fluid were centrifuged over the prolonged test periods. The application of a voltage across the fluid had a negligible effect on this particle migration. The effect of particle migration due to centrifugal and electro-static effects indicate future development requirements for these smart materials.

Thermal equilibrium in a dynamic electrorheological fluid model of a high-speed traversing/positioning mechanism

A high speed traversing/positioning mechanism using two electro-rheological clutches is described. The traversing mechanism can be used to wind filaments onto bobbins. The traverse speed is 5 m/s, the required turn round period is 10 to 20 milli-seconds, the traverse length is 250 mm, the turn around position must be controllable and repeatable within +/- 1 mm and the traverse requires to be controlled to shape the resulting bobbin ends. These combined criteria of high speed and controllability makes the use of electro- rheological fluids a potentially viable solution. A dynamic simulation is available to predict the performance of the mechanism, however, a number of the electro-rheological fluid properties required by this simulation are temperature dependent. The methodology for predicting the thermal equilibrium temperature of the electro-rheological fluid within the high speed traversing mechanism is presented. Heat generation within the electro-rheological fluid, due to the fundamental operating mechanics of the mechanism, shearing of the electro-rheological fluid and the electrical excitation, are combined with the heat transfer from the mechanism to enable the operating temperature of the fluid to be determined. This operating temperature enables the temperature dependent fluid properties to be used in simulating the dynamic performance of the mechanism.

Control Indications for an Inertial Drive Clutch Using Electro-Structured Fluid under Cyclic Operation

The effects of various characteristics of an electro-structured fluid on the performance of a typical lightweight, high speed, flexibly operated inertial mechanism are investigated with a view to determining optimal matching of one to the other and as a basis from which to decide a control strategy. Values of the electron-hydraulic time delay and limiting yield stress of the fluid are varied between typical current values and those considered to be practically achievable within the next few years. The interplay of these with the viscosity of the fluid at zero excitation is shown.

Design and Control Considerations for a High-Speed Electro-Rheological Traversing Mechanism:

A high-speed traversing mechanism using two electro-rheological clutches is described. An application of the traversing mechanism is in winding textile filaments onto spinning or weaving bobbins. The design specifications are a traverse speed of 5m/s; a turn round period of 10-20 ms and a traverse length of 250 mm. The turn round position must be controllable and repeatable within ± 1 mm and the traverse length requires to be periodically varied in order to shape the ends of the resulting bobbin. These combined criteria of high speed and controllability makes the use of electro-rheological fluids an attractive proposition. The paper considers the effects of the main geometric and fluid parameters on the performance of the mechanism and uses this to outline the limiting performance of the mechanism, together with the effects on the precision of the mechanism. The paper also outlines control aspects of the mechanism and uses this to indicate important areas for consideration in the future development of electro-rheological fluids.

ESF Clutch Driven Mechanisms and the ER Linear Reversing Motion Demonstrator

The ESF clutch is formed by enclosing fluid between driver and driven plates and exciting it magnetically or electrostatically, or both, thereby enabling a torque or force transmission depending on whether the applied motion is rotary or linear respectively. Generally the more rewarding ESF clutch applications drive an inertial type of intermittent load, otherwise highly developed, mechanical and electrically closed or opened clutches are preferable on a cost and convenience basis. If a shaped motion is called for servo or stepper motors would be natural first choices. It follows that if the ESF clutch is to be employed it must have something special to offer and this derives from a combination of rapid switching capability and low output side inertia, see Figure 3.1.

Optimization and control of a high-speed electrorheological traversing mechanism

A high-speed traversing mechanism using two electro- rheological clutches is described. An application of the traversing mechanism is in winding filaments onto bobbins. The traverse speed is 5 m/s; the required turn round period is 10 to 20 milli-seconds; the traverse length is 250 mm; the turn round position must be controllable and repeatable within +/- 1 mm; and the traverse requires to be controlled to shape the resulting bobbin. These combined criteria of high speed and controllability makes the use of electro-rheological fluids an attractive proposition. The paper considers the optimization of the traversing mechanism; both geometric and fluid parameters are considered. The limiting performance of the mechanism is detailed together with the effects on the precision of the mechanism. The paper also outlines control aspects of the mechanism and uses this to indicate important areas for consideration in the future development of electro- rheological fluids.

Interactive dynamic, thermodynamic and electrical studies on an electronically adjustable ER linear reversing mechanism

An exercise for balancing the heat generated in and the cooling capacity of a digitally operated, clutch based, ER variable motion configuration mechanism is highlighted. Both electrical and mechanical loadings are considered in conjunction with the natural cooling from a rotating cylindrical clutch surface, temperature dependant fluid properties and inertial parameters. The methodology developed applies to both ER and MR type fluids and indicates pointers to the future development of these fluids for high speed machines.

Simulation, performance, and experimental validation of a high-speed traversing/positioning mechanism using electrorheological clutches

A high speed traversing/positioning mechanism using two electro-rheological clutches is described. The traversing mechanism can be used to wind filaments onto bobbins. The traverse speed is 5 m/s, the required turn round period is 10 milli-seconds, the traverse length is 250 mm and the turn round position must be controllable and repeatable within +/- 1 mm. These combined criteria of high speed and controllability makes the use of electro-rheological fluids an attractive proposition. Simulations produced using a dynamic model are compared with experimental results and these validate the simulation techniques. The effect on the performance of various fundamental electro-rheological fluid characteristics, namely electro-rheological shear stress, electron-hydraulic time delays and zero volts viscosity are considered together with the design of the mechanism. This illustrates the need for optimization of such mechanisms to meet the varied and difficult design requirements found in high speed controllable devices. Some practical difficulties in achieving a reliable mechanism are also discussed.