PIMag® Magnetic Direct Drives

Voice coil drives are single phase motors consisting of a permanent magnet and a winding body that are located in the air gap of the magnetic field. When current flows through the winding body, it moves in the magnetic field of the permanent magnet. Particularly compact dimensions can be achieved when rectangular or flat shapes are built.

Cylindrical voice coils are constructed according to the plunger coil principle (i.e., the coil sits in a field assembly). Either the winding body or the field assembly can be moved. With the so-called multi-coil principle, the motor constant of cylindrical voice coil motors can be optimized in compact installation spaces and even solutions with hollow shafts can be realized, for example. Voice coil drives are suitable for scanning applications that require high precision, high dynamics, and high velocities at travel ranges up to ten millimeters.

A classical 3-phase linear motor is basically a series of at least three (or a multiple of three) voice coil motors. The individual coils can be controlled according to a position-dependent, fixed pattern (i.e., commutated). Linear motors are used both for very high and for very low feed velocities. They work precisely in a range from below 0.1 µm/s to more than 5 m/s. If combined with air or magnetic bearings, a position resolution down to a few nanometers is possible.

Optionally, under vacuum, PI can apply a special epoxy resin to its linear motors. This results in an improved heat dissipation, whereby higher nominal forces can be achieved. In addition, the sealing compound ensures that the motor is encapsulated and therefore protected against external damage (e.g., during assembly). For applications that require high velocities or fast current rise times, PI can design motors for very high operating voltages of up to 600 VDC.

The magnetic tracks used in PI linear motors are available in various lengths, they can be connected in series in order to realize any desired travel range. Single-sided or U-shaped magnetic tracks are available.
U-shaped magnetic tracks achieve higher magnetic field strengths and thus higher forces than single-sided magnetic tracks. If the magnets are additionally arranged as a Halbach array, the magnetic field strength can be increased by about 10% compared to a North Pole to South Pole arrangement. In addition, the iron counterplate can be omitted in a Halbach array, making these magnetic tracks significantly lighter. The advantages of using a Halbach array also apply to single-sided magnetic tracks. In this case, the use of Halbach arrays minimizes stray fields on the rear side. PI offers carbon supports for applications that require ultra-light magnetic tracks.

The winding body of ironless linear motors does not have an iron core. This means that there are no attracting forces between the coil and the magnet assembly and cogging does not occur. The lack of an iron core also reduces the weight of the motor itself. Since there is no cogging that affects the guides and feed velocity, and the winding body is lighter, ironless motors are characterized by high travel accuracy, high velocity stability, and high accelerations. Power and dynamics requirements can be met by increasing the number or the dimension of the motor coils. In most cases, ironless motors achieve lower nominal and peak forces than iron-core motors. This is due to the lack of thermally conductive metals in the design and the resulting limited heat dissipation from the coils. The motors are, therefore, protected against overload by means of temperature sensors.
Ironless linear motors are suitable for applications requiring high dynamics in a compact installation space, while having the highest demands on precision.

In principle, a torque motor is a linear motor that is arranged radially. The stator of the torque motor contains coils and is firmly mounted; the rotor contains the magnet assembly. While the magnet length scales linearly, the torque scales quadratically with the diameter. Therefore, large torques are generated on a large diameter. In addition, large radial dimensions make it possible to create apertures for the passage of laser beams or cables.

Because of the direct drive principle, torque motors are backlash free. The zero-play allows high positioning accuracy and high drive rigidity, resulting in high repeatability. The high drive torque enables high acceleration and therefore high dynamics. Additional features include high torsional rigidity, high peak torques, high degrees of efficiency, as well as very smooth running.

Among others, torque motors are suitable for high load rotation stages on single or multi-axis assemblies thanks to their compact design with respect to torque and rotational symmetry.