The word piezo is derived from the Greek word for pressure. In 1880 Jacques and Pierre Curie discovered that pressure generates electrical charges in several crystals such as quartz and tourmaline; they called this phenomenon the piezoelectric effect. Later they noticed that electrical fields can deform piezoelectric materials. This effect is called the inverse piezoelectric effect.
THE PIEZO MOTOR TECHNOLOGY
The piezoelectric effect
Advantages of the piezo technology
High precision
Piezo LEGS® can easily position on a sub-micron level, or even down to sub-nanometers. The resolution depends on the electronics; the limiting factor is not the motor itself. With the possibility to microstep down to sub-nanometer, you can achieve a truly smooth motion.
No backlash
A controlled linear motion without backlash is accomplished without the need of gearboxes or ball screws – the motor responds instantly. The true direct drive enables a combination of high precision and a dynamic speed range. Piezo LEGS® is self-locking and will hold load even when powered off.
Non-magnetic
The drive unit in the Piezo LEGS® is non-magnetic. This enables motor designs suitable for high-magnetic environments or where magnetic disturbance is an issue.
Compact designs
The motor has a compact design which fits perfectly in OEM applications.
The system
To run a piezo motor you need electronics, as in all modern motion control. The core of the motor is a multi-layer piezo ceramic, a component with high performance at low voltage. By applying controlled electrical voltage to the ceramic, a linear or rotary motion is created.
To keep control of the position, an encoder is required. The resolution of the system depends on both the encoder resolution and the electronics resolution.
One of the greatest advantages of piezo-based systems is the combination of high precision and quick response time without increasing cost of the system.
A piezo motor-based system has a true direct drive, meaning that the object to be moved is directly connected to the piezoceramic actuator legs in the motor via the drive rod of the motor. This has the important advantage of giving no backlash, quick response time, and high resolution. This enables short cycle times in repeated move-and-settle applications reducing overall processing time.
Controller
Motor with drive rod
Encoder
The motor
Piezo LEGS® work with friction drive, where force is created by the internal preload of the piezoceramic actuator legs in direct friction contact with the rotor or drive rod. When the legs start walking, they are always in mechanical contact with the drive rod.
1
Voltage is applied to both left and right, causing the leg to extend to its fullest length
2
Voltage is applied to the left part of the leg, causing the leg to extend to the right
3
No voltage applied to the leg
4
Voltage is applied to the right part of the leg, causing the leg to extend to the left
The electronics
A controlled motion is created by applying voltage signals to the ceramics. The step length depends on the load as shown in the figure below. One full step can be divided into several thousands of microsteps. The length of a microstep reaches down to sub-nanometer level.
Waveform optimized for high microstep resolution
A microstep = a fraction of the waveform (full step); e.g. 8192 microsteps per waveform.
1 microstep, less than 1 nm
