Patent ID: 7789849

Claim:
A peritoneal dialysis system comprising: an enclosure; a stepper motor housed by the enclosure; a pump head in operable communication with the stepper motor; a disposable unit including at least one flexible membrane attached to a rigid piece, the enclosure and the disposable unit configured to allow a negative pressure to exist between the pump head and the flexible membrane and to pull the flexible membrane to a position that extends beyond a relaxed position of the membrane, the enclosure configured to receive the disposable unit such that the stepper motor can move the pump head towards and away from the flexible membrane to cause, the flexible membrane to move outwardly with respect to the rigid piece as the pump head is moved away from the disposable unit, and the flexible membrane to move inwardly with respect to the rigid piece as the pump head is moved towards the disposable unit; and an encoder operable with the stepper motor to indicate a position of the pump head after the pump head has moved towards or away from the flexible membrane, the encoder configured to indicate the pump head position after a power loss.