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Disclosed is a compensation method to cancel thermal drift of a VCM (voice coil motor) torque by using the resistor which has a specific TCR (thermal coefficient of resistance).
English (United States)
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Compensation Method for Thermal Drift of Voice Coil Motor Torque
Disclosed is a compensation method to cancel thermal drift of a VCM (voice
coil motor) torque by using the resistor which has a specific TCR (thermal
coefficient of resistance).
The VCM is used as an actuator drive element which translates coil current
into force or torque an shown in Equation 1 below. F = k * I (1) where F = torque,
k = torque coefficient and I = coil current.
The torque coefficient 'k' depends on temperature. Let 'k(T)' be the function
of temperature (T). F = k(T) * I (2)
The 'k(T)' has negative correlation to temperature and it can be assumed as
a linear function of temperature on all ranges of the operating temperature (see
As seen from Equation 2, the effect of temperature can be canceled with coil
current 'I(T)' which is the function of temperature (T) and is in inverse proportion
Specifically, the thermal drift of VCM torque is cancelled by using a VCM
drive circuit shown in Fig. 2. In Fig. 2, R1 has no TCR, and R2 has a specific
TCR whose value is negative to the thermal coefficient of VCM torque. However,
the temperature around R2 is near that around VCM.
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