Drive Wave Generation Circuit for Lens Position Detection
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Solution Overview
Problem
Piezo actuators used in devices like camera lenses face challenges in determining the absolute position of movable objects without position detectors, and existing solutions require complex voltage waveforms to control movement speed, which complicates downsizing and cost reduction in applications like cellular phones.
Innovation Solution
A drive wave generation circuit that outputs two types of drive waves based on count values, allowing for determination of the initial lens position by mechanical limits without a position sensor, and uses an enable signal to control the circuit's operation state, eliminating the need for a specific initial operation signal and reducing terminal requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lens position detector is provided to determine the absolute position of the lens, then the position detection accuracy is improved, but the device size and cost increase
Solution Approach 1:
The piezo actuator system determines its own initial position by utilizing the mechanical limit position of the lens and the characteristics of its drive waves, without requiring an external position detector. The system serves itself by using the relationship between drive wave application and lens movement to infer position information
Solution Approach 2:
The system performs preliminary movement of the lens to the mechanical limit position before normal operation begins. This preliminary action establishes a known reference point (the limit position) that enables subsequent position determination without sensors
2Speed
If complex voltage waveforms are used to control movement speed, then the drive shaft speed control is improved, but the circuit complexity increases
Solution Approach 1:
The system controls movement speed by changing the parameters of the drive wave (voltage application pattern) rather than using complex waveform shapes. By varying voltage application timing and duration based on the counter value, the system achieves speed control with simpler circuitry
Solution Approach 2:
The drive wave parameters are dynamically adjusted based on the counter value during operation. The system transitions from slow elongation to quick contraction by changing voltage application patterns, achieving variable speed control through dynamic parameter modification
3Ease of operation
If a specific initial operation signal terminal is added to control the initial operation, then the control precision is improved, but the number of terminals and circuit complexity increase
Solution Approach 1:
The enable signal terminal serves multiple functions: it activates the piezo actuator circuit and simultaneously triggers the initial position determination operation. This multi-functionality eliminates the need for a separate initial operation signal terminal, reducing the total terminal count while maintaining control precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise determination of the initial lens position without sensors, simplifies the circuit design by eliminating unnecessary terminals, and facilitates reduced processing load and cost-effective miniaturization in devices like cellular phone cameras.
Implementation Method 1
a voltage is applied to a piezo element (piezoelectric element) so as to cause elongation and contraction of the element, thereby generating a reciprocating movement of a drive shaft
Data Source
AI summary
Two standard waves from a standard waveform generation circuit are output via an output gate while being interchanged by a direction selector. The switching operation of the direction selector is controlled by a direction control signal M/I. 200 cycles of the standard waveforms are counted up by a 200-cycle counter. A drive counter is downcounted every 200 cycles, while the drive counter is upcounted in accordance with the number of drive pulses DRIVE. When the count value of the drive counter becomes zero, output from the output gate is thereby stopped. At the time of startup, outputs from the 200-cycle counter are counted so as to output a drive wave in a predetermined number in a predetermined direction.