FAQ
Answers to frequently asked questions
Where can I use the Elliptec Motor?
The motor may be used for any actuation task within its technical limits. Linear and rotary motions without stroke limit are possible. The Elliptec Motor is quiet, light, precise, and economically priced. The motor can be used wherever alternative solutions are too big or too costly. Several motors may be used in parallel in the case that the required forces are too big, or that motor speed is too small where gears or levers are used.
How temperature sensitive is the motor?
With appropriate rotor materials, the motor may be operated at temperatures from -40°C to higher temperatures run the risk of depolarizing the piezoelectric element over time. A constant voltage of 56V re-polarizes the motor again. Re-polarization may be done in situ. The use of heat-resistant rotor materials is critical at higher temperatures. A change in temperature causes a small shift in the motor’s frequencies of operation. Also, the RC-oscillator frequencies of the microcontroller change over temperature. Both effects are readily compensated by the controlling software.
What is the life expectancy of the motor?
The motor power depends on the material of the driven element. With a PF7595 rotor, the stroke distance before failure is approximately 40 km at low mechanical loads. It should be noted that motor power is model dependent.
What is the supply voltage for the motor?
The motor itself is controlled with amplitudes of 5 – 8 Volts rectangular or up to 10 V sinus. The supply voltage of the control electronics may be 2.4 – 30 V. The appropriate final stage design needs to be selected according to the supply voltage.
What is the power consumption of the control electronics?
1-450 mA @ 5 V. The current draw depends linearly on motor speed.
How does the motor react to water?
The Elliptec Motor is insensitive to water and does not corrode! However, operation is not possible when submerged. Lacquer can be applied to insulate the open electric contacts.
Can the motor be used in vacuum?
The motor may be used in vacuum if wires without polymer insulation are used.
Can the motor be operated on solar energy?
In a typical solar-powered application, a small capacitor would store the electric energy from the solar cell until the voltage is sufficient to move the motor a small distance. Energy of only 0.5mWs is necessary for that purpose since the motor is extremely responsive. Therefore, the load capacitors can be much smaller than in a corresponding solar-powered design with DC motor. If the required speeds are small, the solar panels may be significantly smaller than in DC motor solutions.
What is the frequency of operation?
The frequencies of operation are in the inaudible (supersonic) range of 73-108 kHz. There is a frequency for forward motion and one for backward motion.
What force does the motor generate?
Blocking force: typical 0.8N (friction clutch).
Driving force: 0.2N. The force can be amplified with levers or several motor in parallel.
How fast is the motor?
The zero-load, maximal speed is typically over 300mm/s. There are two methods to reduce the speed in the software:
Speed reduction with internal PWM (Pulse Width Modulation)
The microcontroller produces a digital signal that the final stage (consisting of two transistors and an inductive element) converts into a sinusoidal signal. Maximal thrust is achieved if the digital signal has equally long high and low periods (50% duty cycle). When the duty cycle is changed, the power available to the motor is reduced and therefore also the speed. The downside to this method is that the motor force is simultaneously reduced so that the motor may get stuck at very small speeds. A feedback system can help to alleviate this problem.
Speed reduction with external PWM
The motor is operated for a very short period at its frequency of operation with the optimal 50% duty cycle. During this period, speed and force are maximal. Thereafter, a brief pause is inserted (zero volt at the motor) so that the driven element does not move. The driven element, therefore, moves in small steps. Since the steps are very small and occur in quick succession, the motion appears to be continuous. The durations of the on and off periods determine the average motor speed as well as the step size and the step frequency. This method has the advantage that the motor force remains constant.
Both methods can be combined in order to optimize force, speed and even noise generation.
What are the precision and the dynamic properties of the motor?
The Elliptec Motor has transients of less than 100 µs after which the full driving force is reached. The resulting acceleration, a, is simply given by the equation F = m • a, where F is the drive force that depends on the rotor material and m is the accelerated mass. Braking occurs similarly fast, with the braking force being approximately equal to the blocking force. The resulting braking and acceleration times are extremely short. This property is the basis for the exceptionally high precision of the motor. Smallest motion steps may be achieved with very short signal pulses. Transients are very brief. The positioning error depends on the rotor material and can be less than 1 µm. A position feedback system allows positioning accuracies of a few µm. The final position can then be reached with maximal speed. (PS. Accerelation curves can be found in the down load area. See also Positioning application note)
The final position may be precisely reached thanks to the extremely short brake period. If this precision is still insufficient, the motor may additionally be used in an actuator mode by applying a DC voltage of 0 – 40 V so that most accurate positioning in the sub-micrometer range is achieved.