Answering Your FAQ's About Piezo Technology

Can you count the number of steps and know your position?
Normally not, the Piezo LEGS motor has a friction coupling between the motor element and the drive rod or rotor disc. This means that under constant load there is a certain variation between different steps (under constant load normally between 5% to 10%, under varying load this figure can be much higher). Therefore, to know your position accurately you need a position sensor or some other feedback loop from your motion system.

How slow can a motor a Piezo LEGS motor run?
One of the great advantages with a Piezo LEGS motor is that you can run the motor extremely slow. As an example you can, with the PMD101 driver, run a linear Piezo LEGS Linear 6N motor down to a speed of a few nanometers/second, with more advanced drive electronics even slower.

How fast can a Piezo LEGS motor run?
The speed of a motor is based on the maximum step length and the maximum step frequency.

For a Piezo LEGS Linear 6N motor, the maximum speed is around 20mm/sec at no load (7 micrometer x 3,000Hz). Higher speeds can be obtained with custom motor designs. There is also a correlation between force and speed – the higher the force the lower the speed, as well as regarding size – the bigger the motor (higher force) the lower the maximum speed.

I am considering a motor for a portable operated device and battery life is therefore a concern. How efficient is the motor?
A Piezo LEGS motor can be very energy efficient compared to other more conventional motor alternatives like DC motors, but it will depend on the application. This speaks in favor of a Piezo LEGS motor that it does not consume any power in hold position and that the motor does not have any inertia and peak currents when starting or stopping. Another factor that speaks in favor of the Piezo LEGS motor is that it is direct driven and therefore does not need a gearbox or linear screws. All in all you can say that the more intermittent duty cycle your application require the better chance you have to gain in battery life with a Piezo LEGS motor.

What is the difference between holding force and stall force?
The stall force is the highest load a motor can deliver (a running motor will stop when load reaches this value) without slipping backwards. Holding force is the highest load a motor can statically hold (the motor is not running/power-off) without slipping backwards. Holding force is generally about 10% higher than stall force, this is due to the fact that the contact situation and friction is improved when the motor is powered-off.

What is the difference between full steps, reduced steps and micro stepping?
The operating principle of the Piezo LEGS motor is very similar to walking – the grip and release action of our feet as we walk on the ground. In a Piezo LEGS motor, the legs of the piezoelectric motor element grip the drive rod or rotor disc, move it forward and release it, and then the next pair of legs repeat the same action. Just as we humans, the motor has the ability to take long steps or short steps; this is called full steps and reduced steps respectively. It is also possible to dived a full step in a number of smaller increments, this is called micro stepping, the smaller the increments the higher the resolution of the motor (= the motors ability to take small steps). The resolution is ultimately dependent on the drive electronic used (single nanometer or even sub nanometer resolution is possible).

Will the Piezo LEGS motor be damaged if it is run into a hard stop?
The motor will not be damaged if it is run to a hard stop. It is also possible to manually adjust the position of the drive rod without damaging the motor. The friction coupling between the drive legs of the motor element and the drive rod has been designed so that no critical forces will be reached in the motor elements.

Can the force of the motor be adjusted?
The force is determined by the normal force, the spring force that presses the drive rod against the legs of the drive element. The normal force, and thus the force of the motor, can be adjusted by the number of springs used (up to a maximum value dependent of the size of the motor element).

Must I use drive electronic supplied by PiezoMotor?
No. Most OEM customers have designed their own drive electronics and all relevant information to facilitate this will be supplied to customers on request.

In what temperature range can the Piezo LEGS motor be operated?
Piezo LEGS motors are normally specified for a temperature range of -20°C to +70°C. The specifications of the motors are given at room temperature and the performance of the motor will be lower for lower temperatures and higher for higher temperatures. For specific values, please contact PiezoMotor. For motors requirements outside the normal temperature range please also contact PiezoMotor.

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