Linear thinking about motor

When most engineers hear the word motor, they naturally think of rotation devices, such as brush DC, brushless DC, stepping motor, or frequency conversion motor. However, the motor does not necessarily rotate, and many times the design requires straight-line motion. One solution is to add a gear or belt mechanism to convert the rotating motion, which works well in many cases. However, it may be too complex, too expensive, too heavy, have a rebound problem, or not a good match at all.

A direct way to obtain the desired linear motion is to "unfold" the stator of a conventional rotary motor, which has been successfully used for long stroke requirements. However, for a few inches of travel distance, there are two effective, essentially linear alternatives: a voice coil actuator (VCA), commonly referred to as a voice coil motor (VCM) and a piezoelectric motor. They operate on distinct principles from each other and therefore provide different performance attributes.

As the name implies, the VCA was developed to drive the speaker's paper basin, which also provides considerable experience in mass market design and manufacturing. The design and construction of the VCA is very simple, with permanent magnet and black steel field components and coil components. The current flowing through the coil group interacts with the permanent magnet field to produce a force perpendicular to the current direction. The direction of this force can be simply reversed by reversing the current.

The VCA can be constructed to move the coil component or the magnetic field component (Fig. 1 and Fig. 2). For the former, the wires connected to the coil must be thin, light, flexible and not be laid out to fatigue or break due to constant bending - perfected through the production of billions of speakers. Typical VCA displacements are two to three inches, but construction units can be used to double that distance. They provide several ounces to hundreds of pounds of force and control the position of moving elements.

The schematic diagram and cross section of the moving coil VCA show its simplicity. This arrangement is used in the speaker to control the speaker cone. Group Six M, LLC

The schematic diagram and cross section of the magneto-dynamic VCA show that it is a physical complement to the dynamic coil arrangement. Group Six M, LLC, even if you've never used VCAs directly, certainly benefit from them: they are the standard for locating disk drive heads. Given the compact track density of the driver and the positioning requirements of the application, you can have a good understanding of the accuracy, control, speed and motion control profiles provided by the VCA.

But why limit the idea of linear motors to electromagnetic principles? As the name implies, a piezoelectric motor is based on the well-known principle of symmetry, that is, the effect of an applied electric field on the size stability of a crystal, and vice versa: when a crystal material is subjected to mechanical stress (compression), it generates a voltage; And when a voltage is applied to the same crystal, the material expands by a very small amount.

In a piezoelectric motor, the voltage at both ends of the crystal produces an electric field, and the material is very slightly elongated. For a typical applied voltage, it is approximately 0.001% to 0.1%. Crystals are usually small (usually 10mm in each dimension), and the resulting motion can be controlled at the micron level, but requires Newton's force. Piezoelectric motions are used in infusion pumps, microscopic carrier platforms, optical positioning systems, instrumentation, inkjet nozzles, semiconductor processing machines, etc. They are non-magnetic (a major advantage in many cases) and do not have bearings that need lubrication (which can cause pollution).

The piezoelectric material can move forward like a worm by fixing it in an alternately fixed and loosened jig (Fig. 3), or by fixing one end in place while allowing the other end to move back and forth with the voltage applied and removed, resulting in a micro-piston motion (Fig. 4).

Piezoelectric motors can crawl forward in small increments like inches, with proper clamping and loosening times for power on and off (1: housing, 2: moving crystal, 3: locking crystal, 4: rotating part). DATA: Wikipedia user Laurens van Lieshout

The piezoelectric motor becomes a highly controllable piston with one end fixed in place during power and power outages. DATA: Wikipedia user Inductiveload differs much more than size, travel, force, speed and other performance parameters because they also require very different driving signals. As an electromagnetic-based unit, the VCA needs to be driven by analog current, although it can be at low voltage. In stark contrast, a piezoelectric motor is a voltage-based device that requires a voltage from 50V to thousands of volts and a low to moderate current to provide sufficient power. IC and modules are designed for this situation. As a result, designers of VCM drives often focus on IR voltage drop and use thicker wires, whereas designers of piezoelectric drives must focus on security issues related to high voltage - a big difference of opinion.

Therefore, when you are looking for linear motion solutions for unique applications, consider using a well-known alternative to rotary motors and associated motion "transformers", since inherent linear motors may be a better choice. Or effective