Method and apparatus for measurement and control of magnetic particle concentration in a magnetorheological fluid

An integrated fluid management module for use in a magnetorheological finishing system having a carrier wheel, comprising:

• a) a housing having a magnetically-shielded chamber therein, said chamber having an opening to a surface of said carrier wheel;
• b) apparatus for receiving and replenishing spent magnetorheological fluid within said chamber;
• and
• c) a ribbon extruder mounted to said housing for extruding a ribbon of replenished magnetorheological fluid from said chamber onto said wheel surface,
• wherein said replenishing apparatus comprises,
• i. a sensor system for determining concentration of magnetic particles in said spent magnetorheological fluid, wherein said sensor system comprises a first wire coil disposed in a housing defining a sensor having only one end in liquid contact with said magnetorheological fluid and an AC voltage generator attached to said first wire coil in an electrical circuit, such that when said generator is energized a magnetic flux field is created in and around said first wire coil, wherein said magnetic flux field includes fringing fields extending beyond the opposite ends of said first wire coil, and wherein, when either but not both of said fringing fields extending beyond the opposite ends of said first wire coil also extends through said magnetorheological fluid, the impedance in said circuit is proportional to said concentration of magnetic particles, and a second wire coil connected to said generator and identical to said first wire coil and having fringing fields outside of said magnetorheological fluid, wherein said first wire coil is a sensing coil and said second wire coil is a reference coil;
• and
• ii. a controllable dispensing apparatus for adding a calculated amount of replenishing fluid to said spent magnetorheological fluid,
• wherein impetus for receiving and replenishing said spent magnetorheological fluid within said chamber and for extruding said ribbon of replenished magnetorheological fluid from said chamber onto said wheel surface is provided by the motion of said carrier wheel past said integrated fluid management module.