Motor Driving Apparatus Gain Variation Reduction
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Solution Overview
Problem
Conventional motor driving apparatuses experience significant variations in gain when the drive current is small, leading to inconsistent motor performance across different devices due to variations in circuit constants.
Innovation Solution
The motor driving apparatus incorporates a rotational position detecting unit, a D/A conversion circuit, and an error amplifier circuit to generate sinusoidal signals and control drive voltages, with a resistor string and switch elements to minimize the impact of circuit constants on gain variations, ensuring consistent performance even at low drive currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional PWM drive control is used with analog sinusoidal signals from hall amplifier, then the motor can be driven with simple circuit configuration, but gain variations occur when drive current is small due to circuit constant variations
Solution Approach 1:
The patent replaces the conventional analog multiplication circuit with a digital signal processing approach. Digital sinusoidal signals are generated by a ROM storing sine wave data, and the analog multiplication is replaced by digital-to-analog conversion of the product of digital signals and error amplifier output. This substitution eliminates the gain variations caused by analog circuit constant variations while maintaining circuit functionality.
Solution Approach 2:
The patent changes the signal representation from continuous analog sinusoidal signals to digital sinusoidal signals stored in ROM. The analog multiplication operation is replaced by digital signal processing where the transfer coefficient becomes independent of circuit constants. This parameter change from analog to digital domain resolves the gain consistency issue at low drive currents.
2Reliability
If digital sinusoidal signals are generated using ROM and D/A conversion, then gain variations are reduced, but device complexity increases
Solution Approach 1:
The patent replaces complex analog multiplication circuits with a digital signal processing system using ROM and D/A converter. The ROM stores pre-calculated sinusoidal wave data, eliminating the need for analog function generators and multipliers. This substitution reduces sensitivity to circuit constant variations while the overall complexity is managed through integration of these components.
Data Source
AI summary
There is provided a motor driving apparatus in which variations in individual circuit constants have a small effect even when a drive current is small. An error amplifier circuit amplifies a difference between a current detection signal showing a current value of a drive current that flows in the motor and a drive command signal controlling the drive current and converts an amplified difference into a current to output the current as an error amplifier current signal. A D/A conversion circuit generates a sinusoidal signal from the error amplifier current signal based on a digital signal sequence outputted from a rotational position detecting unit. It is preferable that a transfer coefficient of the error amplifier circuit is inversely proportional to the resistance value of the D/A conversion circuit.