20N Short Travel Flat Linear Voice Coil Actuator for Optical Lens Auto Focus

The VCAP0020-0068-00A is a flat, coreless planar voice coil actuator designed specifically for optical focusing axes, where installation space is measured in millimetres and the rise time directly determines the throughput of the entire device. At 25°C, this flat moving-coil actuator has a total stroke of 6.8 millimetres and delivers a peak thrust of 20 N and a continuous thrust of 5.5 N, whilst measuring just 39 × 50 × 21.5 millimetres. As the flat coil operates directly within the air gap of the permanent magnet track, there are no screws, belts or gear trains between the electrical command and the mechanical output. Driving force is generated within a few milliseconds, there is no backlash when reversing direction, and the shaft’s repeatability can reach any resolution readable by an external encoder. With a maximum terminal voltage of 8.2 V and a back-EMF constant of 4.4 V/m/s, the flat voice-coil motor can be easily driven by a compact 12 V or 24 V servo amplifier with a low current loop.

Currently, the focus axes of most lenses are still comprised of stepper motors and lead screws. Whilst this combination is inexpensive, friction, hysteresis and screw resonance limit the available bandwidth to a few hertz, which is precisely what causes the focus search speed to slow down during high-magnification inspection. Removing the transmission mechanism radically alters the entire dynamic model: the output force is proportional to the coil current, the focus axis behaves as a simple moving mass, and a single high-gain controller can simultaneously meet the requirements of both slow tracking and fast step-and-hold motion. As there is no mechanical compliance to generate vibrations, nor any need for lubricant redistribution, this flat linear actuator also supports sinusoidal scanning at hundreds of hertz for optical sectioning. Straightness is determined by the guide rails or flexible components supplied by the customer, whilst an external linear encoder can maintain closed-loop positional accuracy to 0.1 µm or better. With a height of just 21.5 mm, two or three focus axes can be stacked within a single optical head without the need to redesign the optical path; furthermore, the low mass in motion ensures that the reaction forces acting on the frame are sufficiently small, making it suitable for vibration-sensitive laboratory benches.

Machine vision inspection heads, laser and fibre marking focus units, camera module active alignment, microscope autofocus for life science instruments, semiconductor optical metrology, wafer edge inspection, high speed code readers on packaging lines, and any short travel zoom, iris or shutter mechanism that has to cycle thousands of times per hour.

Q: Does the actuator hold position when the power is switched off?
A: No. A voice coil produces force only while current flows. If the axis has to stay in place with the drive disabled, add a counterweight, a light spring or a mechanical brake, otherwise the load will drift.

Q: Which driver should be used with this model?
A: Any DC brush servo amplifier with a current loop rated above 3 A and a 12 V or 24 V bus is suitable. Current mode is preferred, because force is then proportional to the command signal and the loop can be tuned as a pure mass.

Q: Can it run continuously at the 20 N peak rating?
A: The 20 N figure is an intermittent rating used for acceleration peaks. The continuous thermal limit at 25°C is 5.5 N, and this can be raised with a heat sink or forced air on the magnet track.

Q: Is a linear encoder mandatory?
A: For positioning, yes, the encoder defines accuracy and repeatability. For pure force or pressure control, such as contact force in a probe head, the actuator can be run open loop from a current command.

Q: Can the stroke, cable exit or mounting holes be customized?
A: Yes. Coil winding, usable stroke within the planar family, lead wire exit direction, thread depth and mounting pattern can all be adapted. Samples start from one piece.

Delivered as actuator with mounting screws and wiring diagram. Matching servo drives, linear encoders and flexure guided stages can be quoted together on request.