Abstract: A device for positioning a body (5) by means of at least two electromagnets (13, 15). A position sensor (29) measures the size of an air gap (23) between one of the electromagnets (13, 15) and a guide beam (1). An output signal of the position sensor (29) is applied to an electronic control unit (35) which passes a control current through the electromagnets (13, 15) in dependence on a difference between the measured and a desired size of the air gap (23). An electronic multiplier (47, 59) is connected between the control unit (35) and each of the electromagnets (13, 15), multiplying a control signal from the control unit (35) by the output signal from the position sensor (29). In this way a force exerted by the electromagnets (13, 15) on the guide beam (1) depends exclusively on the value of the control signal and not on the size of the air gap (23), so that a position-independent control is obtained.

Abstract: A motor-compressor unit comprising a vibration motor (1) having a single-part magnetizable stator (2) in the form of a W, arcuate air gaps (9, 10) being formed between the peripheral surface (6) of the central limb 3 of the W and each of the outer limbs (4, 5) of the W, and an armature (11) which is reciprocatingly pivotable about a motor shaft (12). The armature comprises at least one permanent magnet pole element (13), at least one coil (16, 17) arranged on the stator, an alternating current through the coil producing an oscillating movement of the armature (11), a compressor (21) having a linearly reciprocating piston (24) which is coupled to the armature (11), the coupling (25) being arranged diametrically opposite the pole element (13) relative to the motor shaft (12).

Abstract: A control device (30) for controlling the supply of power to the coils (16A, 16B) of a drive motor (3) for a compressor unit of the resonant-piston type (1). The control device comprises a power-supply circuit (44) for energizing the motor coils from a direct voltage source (45), means (46, 47, 48; 46, 60) for determining a measure (P, .phi.), which indicates whether the power consumption of the motor as a function of the frequency of the energizing current is at least approximately maximal, and means (40, 42, 43; 61, 42, 43) for adjusting the frequency of the energizing current, depending on the derived measure (P, .phi.), to a value for which said measure indicates that the power consumption of the motor (3) is maximal.