ON-OFF EXCITATION SWITCH FOR ER DEVICES

A very important part of any ER fluids based system is the provision o f excitation; this is particularly so since the electrical load is con ductive and highly capacitive. In this environment the surge current a t switch on is large and there are problems in dumping the charge to e ffect a rapid reduction of the voltage level. This paper describes a v oltage switch which when linked to a steady state supply can be used t o effect on-off control. The arrangement is somewhat analogous to the ER catch concept insomuch as it switches one of the ER controller elec trodes either to high potential or to earth rails, the other electrode being permanently connected to earth (just as the catch attaches to a steady input motion or a brake). If the supply has a low output imped ance then the excitation can be rapidly slewed in both ongoing and off going directions. The circuit and its operation is described in detail and brief performance characteristics are shown for the switch when c onnected to a typical, contemporary ER device.