TECHNOLOGY
Recommended drive circuits and choice of driving conditions
1. Analogue drive circuits
Equation 2 gives the current I in amperes drawn from the amplifier, and that figure is the key to choosing one.
Equation 2 does not account for the current drawn by the mechanical system, so we recommend measuring the actual current before selecting a drive circuit.
Equation 3 gives the resistance R in ohms to place between the amplifier and MechaTrans® for an optimum damping factor. Figure 5 shows the arrangement.
2. Digital drive circuits
Figures 6 and 7 show the recommended circuits, and table 3 lists which MechaTrans® series pairs with which circuit.
A step voltage applied through a digital drive circuit produces a large peak current at both the rising and the falling edge, because the actuator is a capacitive device. Add a resistance R or an inductance L between the circuit and MechaTrans® to keep that peak under control.
Where MechaTrans® has to deliver a large amount of kinetic energy, use L rather than R. Equation 4 gives its value, matching the resonance frequency of the drive circuit to the mechanical resonance frequency.
If you need the motion to stop after each input pulse, equation 5 gives the required pulse duration T in seconds.
Even once L has been chosen, the coil core material and the air gap can cause saturation. Contact us and we will design and produce a suitable coil.
Determine Rd in figures 6 and 7 by experiment. In practice it falls between a few ohms and 200 ohms. Choose a resistor with an adequate power rating, since almost all the driving energy in the circuit is dissipated by the coil resistance and Rd together.
For slower motion you can use a resistance Rs in place of L, and you can reduce physical overshoot by shaping the input signal. Please contact us whenever MechaTrans® is used under dynamic conditions.
With L, keep the pulse voltage below 80 V, because the peak seen by MechaTrans® can reach almost twice the base voltage. With Rs, keep it below 130 V, because the peak still exceeds the base voltage.
Not sure which circuit to use?
Send us the actuator, the waveform and the frequency you are driving at and we will recommend a circuit, or supply a matching driver.
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