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SWaP-C Considerations for linear stages vs. voice coil motors

Liquid lenses can adjust focus at various working distances. These small, mechanically or electrically controlled cells contain optical grade liquid, which changes shape when a current or voltage is applied.

A liquid lens design is an alternative worth considering in applications such as:

  • Machine Vision: Utilized in an inspection system to adjust to objects of different heights, for barcode inspection, package sorting, or quality control.
  • Medical Device and Life Sciences: Can replace traditional lenses or lens stacks in microscopy, ophthalmic diagnostic equipment, or imaging devices like dermascopes, to capture images at different depths.
  • UAV Camera Systems: Liquid lenses can quickly autofocus as a drone changes altitude, air temperature, or distance from an object.

Liquid lenses use voice coil motors (VCM), electrostatic, or piezo-electric forces to reshape the lens. Both liquid lenses and conventional lenses require a separate controller to position the lens.

There are tradeoffs to any optical design. Liquid lenses can present cost and time savings in some applications — providing a less expensive alternative for high-volume, price-sensitive products, with autofocus in milliseconds. Conventional optics, controlled by a piezo-electric actuator, offer an advantage in size and weight, due to their embedded controller, and image quality.

Below is a comparison of moving solid optics with M3 modules versus shape-changing liquid optics.

Parameter

Moving Solid Optics
(Using M3 Modules with piezo-driven linear stages)

Shape-Changing Liquid Lens
(Using VCM or electrostatic force)

Motion Size

Smallest, with embedded control electronics and position sensors

Larger, with an external controller

Optics size

Accepts a wider range of high-performance lens assemblies with a larger aperture and higher transmission, to gather more light, and fit the unique optical requirements of the camera

Many are limited to smaller aperture sizes, with the largest around 16mm diameter.

Power consumption

Holds position with no power. Inherent in design. Optimized for power-constrained applications.

VCM requires constant power to maintain position. Not optimal for power-constrained applications.

Orientation

Orientation, relative to gravity, has no impact on image quality when using solid optics. Operating horizontally (perpendicular to gravity) can offer higher payload capacity.

Gravity distortion of liquid lenses can be an issue in some use cases, with vertical imaging required for the highest image quality.

 Transmission

Moving solid lenses are less sensitive to chromatic aberration.

More sensitive to chromatic aberration during focal adjustments. Most imaging is monochromatic (black and white).

Speed

Focus in tens of milliseconds

Electrostatic versions focus in milliseconds

Lifetime

NST specified from 1 million to >10 million cycles

Often specified for >10 million or even 50 million cycles

Other considerations

The M3 focus modules can accept any standard lens size M16 or smaller. M3 linear stages allow mounting of much larger lenses using a mechanical mount, such as a C-mount lens.

VCM version has specific focus settings that require specific current values that generate heat. Calibrated current values, from a look-up table, can change with temperature so a temperature sensor is required.

In practice, liquid lenses may offer cost savings in systems where system size and image resolution are not of primary concern. In applications such as UAVs with color or thermal imaging, where SWaP is critical, and for AR/VR products, where image quality and weight determine customer acceptance, piezo-driven solid optics continue to provide performance advantages.

When considering a moving solid optics design with an M3 piezo-driven linear stage or focus module, our app note on optical and imaging geometry is a great starting point.