A voice-coil motor includes a stator and a rotor, which is pivoted about a swivel axis, with respect to the stator. A conductive film is formed at a rear face of the semiconductor substrate. A motion vector describing a displacement of the object with respect to the surface is generated from such comparisons. The self-service device may also include a monitoring module for determining whether a customer transaction is ongoing. After treatment in the aerobic zone, the wastewater may be treated in other zones, or may be delivered to a liquid-solids treatment stage. Movement of the bolt is preferably controlled using a control valve such as an electronic solenoid valve.