MEMS Mirror Failure Detection Circuit
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Solution Overview
Problem
MEMS mirrors in devices like wafer defect scanners and projectors can fail unexpectedly, causing a high-power laser beam to shine in a fixed direction, leading to potential surface damage, and existing technologies are inadequate for rapid failure detection.
Innovation Solution
A circuit with a mirror position sensor generating an analog output, an analog-to-digital converter, and failure detection circuitry that calculates the difference between digital mirror sense signals at different instants to determine if the difference exceeds a threshold, allowing for quick detection of mirror failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MEMS mirror fails and the rotor becomes stuck, then the laser beam shines in a fixed direction, but damage occurs to surfaces in a very short period of time
Solution Approach 1:
The circuit continuously monitors the mirror position sensor output and calculates velocity in real-time during normal operation, preparing the failure detection mechanism beforehand. When the mirror becomes stuck, the pre-established monitoring system immediately detects the zero velocity condition and triggers laser shutdown, preventing surface damage without requiring additional reaction time.
Solution Approach 2:
The system implements continuous feedback by monitoring the mirror position sensor output and calculating velocity at each instant. The failure detection circuitry compares the calculated velocity against a threshold, and when the mirror becomes stuck (zero velocity), the feedback loop immediately triggers laser beam shutdown, creating a closed-loop safety mechanism that prevents surface damage.
2Reliability
If existing failure detection technologies are used, then detection can be performed, but the response time is too slow to prevent damage
Solution Approach 1:
The patent replaces mechanical or slow electronic failure detection methods with an optical-based sensor system that continuously monitors mirror position and calculates velocity electronically. This substitution enables real-time detection at the speed of electronic signal processing, reducing response time from potentially seconds to microseconds, thereby preventing surface damage before it occurs.
Solution Approach 2:
The system changes the detection parameter from monitoring mirror position alone to calculating mirror velocity by comparing position at different instants. This parameter transformation enables the system to detect stuck conditions (zero velocity) immediately, as the velocity calculation reveals the failure state within a single oscillation period, dramatically reducing response time.
3Reliability
If the laser beam is continuously monitored, then failure can be detected, but the complexity of the monitoring system increases
Solution Approach 1:
The mirror position sensor serves multiple functions: it provides position information for normal laser scanning operation and simultaneously provides the data needed for failure detection through velocity calculation. This multi-functionality eliminates the need for separate failure detection sensors, reducing overall system complexity while maintaining high detection accuracy.
Solution Approach 2:
The system uses its own operational parameters (mirror position sensor output) to detect failures, rather than requiring external monitoring equipment. The velocity calculation is performed using the same sensor that drives the scanning operation, allowing the system to self-monitor and self-diagnose failures without adding external complexity.
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 rapid detection of MEMS mirror failure within a single period of oscillation, preventing damage by quickly switching off the laser beam, thus ensuring safety and reliability.
Implementation Method 1
a mirror position sensor associated with the movable MEMS mirror and that generates an analog output as a function of angular position of the movable MEMS mirror
Implementation Method 2
An analog to digital converter converts the analog output from the mirror position sensor to a digital mirror sense signal
Data Source
AI summary
Disclosed herein is a circuit for determining failure of a movable MEMS mirror. The circuit includes a mirror position sensor associated with the movable MEMS mirror and that generates an analog output as a function of angular position of the movable MEMS mirror. An analog to digital converter converts the analog output from the mirror position sensor to a digital mirror sense signal. Failure detection circuitry calculates a difference between the digital mirror sense signal at a first instant in time and the digital mirror sense signal at a second instant in time, determines whether the difference exceeds a threshold, and indicates failure of the movable MEMS mirror as a function of the difference failing to exceed the threshold.