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1. An assembly comprising an electromagnetic actuator and a motor spindle (17), which comprises, in a spindle housing (19), an electric motor and a spindle (20) which can be rotatably driven by the electric motor, and comprising a tool holder for a tool for workpiece machining, wherein the spindle (20) is designed as a hollow shaft and comprises, in the longitudinal hole therein, a clamping device (22) for firmly clamping a tool or a tool holder, wherein the housing (1) of the actuator is fastened directly or indirectly to the spindle housing (19), and wherein the mobile structure (3) can be brought into operative connection, in a force-transmitting and movement-transmitting manner, with an element (21) of the clamping device (22) which is axially displaceable in a longitudinal hole in the spindle (20), and the clamping device (22) can move into a release position, wherein the electromagnetic actuator comprises a housing (1), two ferromagnetic pole shoes (4, 5) which are arranged at a distance from one another and are rigidly connected to the housing, a mobile structure (3) which can be moved in the housing (1) along an axis between two end positions and is arranged between the pole shoes (4, 5) and comprises at least one magnet system, which structure is connected to a shaft (2) which is axially displaceable in the housing (1), wherein the magnet system comprises radially inner and radially outer pole bodies (6, 7) comprising a magnetic flux-conducting material, at least one arrangement of one or more permanent magnets (9, 10) which are polarized radially with respect to the axis, and an annular coil (8) which can be connected to a current source, and forms, together with the pole shoes (4, 5), an air gap system having axially variable air gaps (L1, L2), wherein the mobile structure (3) can be secured in each of the two end positions without excitation of the coil (8), and can be moved out of the end position, taken up in each case, and into the opposite end position, by excitation of the coil (8).
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