While there are several types of piezo motors on the market, the design and technology employed by DTI in its standing wave-type piezo motors is quite unique and provides certain key advantages in both use and manufacturability. Available in a variety of sizes and configurations, DTI’s full line of rotary and linear piezo motors address many of the modern-day requirements for motion control systems.
DTI’s piezo motors, whether rotary or linear, work on the same principle of electrically induced excitation of ultrasonic standing waves within a piezoelectric resonator/ceramic.
DTI’s new product line has been designed using modern reinforced engineered thermoplastics and is specifically targeted towards high volume OEM applications.
DTI’s differentiated and patented principle of excitation uses two orthogonal modes of vibration with relative phase difference, the resultant motion of the motor is a superposition of the two modes of vibration causing the piezoceramic to oscillate in a way which can be harnessed to create precise continuous rotary and linear motion. This technique (which is part of DTI's IP portfolio) also greatly simplifies drive circuit design and only requires very small voltages, thereby reducing the drive electronics cost. Furthermore, DTI's innovative technique combined with rigorous design philosophy which utilizes a combination of piezoceramics and modern engineered thermoplastics has enabled the company to produce motion products at a very competitive cost.
Another patented technique which DTI has for rotary piezo motors with a ring-shaped piezo resonator and stainless steel pushers is shown in the figure.
Pushers are attached to the piezo resonator through a vibrational shell. An ultrasonic radial standing wave is electrically excited in the resonator causing the ring to expand and contract in radial direction, stimulating movement of the pushers along the radius. Because of their elasticity, the pushers vibrate with the same frequency, although phase shifted, in a direction orthogonal to the radius of the ring. The superposition of the two orthogonal movements results in elliptical movements of the pushers. Because the pushers are held pressed (spring loaded) against the rotor, their movement, via friction at the pusher contact area, causes rotation of the rotor.
DTI’s expertise in the field of standing wave type piezo motor has resulted in the design of several different models, in which the materials and layout have been optimized to provide superior operating performance.
This design has been built into a number of very high performance OEM applications including surgical robots, nano-positioning stages and missile control systems.
CONTROL OF THE
Control of the piezo motor is straightforward using an external signal source applied through three pins located on the driver board (see driver board description for more details). The driver board is typically supplied matched to a specific piezo motor model. Control is achieved by a train of electrical pulses supplied by a digitally controlled AC voltage source directly to the piezoceramic. Motor speed is altered by varying either the repetition rate of the pulses or duration of each individual pulse (i.e. PWM). Modulation of the excitation voltage source enables the piezo motor to rotate (or move sideways) either continuously or in a precise stepping mode.
Learn more about the specific technology details and the key benefits of each DTI product category by clicking on the product categories below (additional information is also provided in each product datasheet):
- Direct-Drive mechanism – provides better accuracy, repeatability and resolution due to elimination of mechanical transmission/gear system. Also abolishes backlash and hysteresis.
- Elimination of the “Stick-Slip” effect – due to unique start-stop characteristics
- High torque with wide range of torques – 10-times better torque (per unit of size/mass) than any comparable stepper motor – enables high dynamic (start-stop) characteristics.
- Low temporal drift – Angular position of the rotor is held fixed (self-braked), providing negligible angular drift (i.e. <1 arc-sec>
- High resolution & high accuracy – <1 arcsec resolution with an absolute positioning accuracy of 4 arc-secs in closed loop mode*
- (using optional high-resolution optical encoder)
- Bidirectional angular positioning – Accuracy one order of magnitude better than the best of currently available systems due to direct-drive mechanism.
DTI’s ultrasonic piezo motors are used around the world in various applications and products within biomedicine, optics, semiconductor and nanotechnology as well as industrial electronic and automotive systems, just to name a few. Click on the animations shown below to see the principle of piezo motor operation in uni-directional and bidirectional modes.
Ring shaped resonator principles of operation (For development)
The word piezo comes from the Greek word “piezein”, which means to squeeze or press. The piezoelectrical effect is best described as the ability of some materials (e.g. piezo ceramics) to generate an electrical charge in response to a mechanical force (e.g. being squeezed or pressed). The piezoelectric effect is reversible, in that materials exhibiting the effect can also exhibit the reverse effect “the inverse piezoelectric effect”. Thus they change shape or size when excited by an electric charge.
Although, the inverse piezoelectric effect has been well known and studied for some years, it is only relatively recently that commercial devices incorporating piezo technology have begun to find practical applications in everyday devices (e.g. focusing mechanism of certain digital cameras, industrial valves, toys etc.).
This situation is now changing rapidly as an increasing number of companies search for alternatives to conventional electromagnetic motors, in order to solve modern day problems associated with the growing demand for; better performance, energy efficiency, miniaturization, and green technology. In a growing number of instances companies are finding that piezo motor technology offers the only efficient and cost-effective answers to these problems.