OHT Carrier Handling With Dynamic Lift Force for Abnormal Locking
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Solution Overview
Problem
In semiconductor fabrication, existing automated conveying systems face challenges in efficiently transporting workpieces between processing instruments, particularly in applying the correct lifting force to carriers of varying weights and sizes, which can result in damage to the workpieces, carriers, and load ports due to abnormal locking conditions.
Innovation Solution
A conveying system with an overhead hoist transport vehicle that includes a control unit to automatically calculate and adjust a minimum lifting force based on the weight of the carrier, number of workpieces, and vertical distance, ensuring safe lifting while preventing damage, and includes sensors to detect abnormal circumstances and alert operators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed lifting force is applied to all carriers, then the conveying system can operate with simple control, but carriers with varying weights may be damaged or not lifted properly
Solution Approach 1:
The lifting force is made dynamic rather than fixed. The control unit automatically adjusts the lifting force based on real-time weight detection from sensors, allowing the system to adapt to carriers with varying weights while maintaining simple operation. The lifting force F is calculated as F = m × g + F_margin, where m is the detected weight, g is gravity acceleration, and F_margin is an additional safety force.
Solution Approach 2:
A feedback mechanism is implemented where sensors detect the actual weight of each carrier, and this information is fed back to the control unit which then adjusts the lifting force accordingly. This closed-loop control ensures reliable lifting while maintaining operational simplicity through automatic adjustment.
2Reliability
If excessive lifting force is applied to prevent abnormal locking, then carriers can be lifted reliably, but workpieces and carriers may be damaged
Solution Approach 1:
The lifting force parameter is dynamically changed based on the detected weight of each carrier. Instead of using a fixed high force that could cause damage, the system calculates the precise required force as F = m × g + F_margin, where the force is directly proportional to the actual carrier weight. This prevents excessive force application while ensuring reliable lifting.
Solution Approach 2:
The system applies only the necessary lifting force with a small safety margin (F_margin) rather than excessive force. This partial action approach provides sufficient lifting reliability while avoiding damage to workpieces and carriers by keeping the force just above the minimum required.
3Reliability
If lifting force is increased for heavier carriers, then all carriers can be lifted safely, but power consumption increases
Solution Approach 1:
The lifting force parameter is dynamically adjusted according to the actual weight of each carrier. The control unit calculates the precise force required as F = m × g + F_margin and applies only that amount, avoiding the waste of energy that would occur with a fixed high lifting force applied to all carriers regardless of their weight.
Solution Approach 2:
The system uses sensors to automatically detect carrier weight and self-adjusts the lifting force without manual intervention. This self-service capability ensures safe handling of heavier carriers while minimizing power consumption by applying only the necessary force for each specific carrier.
Data Source
AI summary
A method for operating a conveying system is provided. An overhead hoist transport (OHT) vehicle is provided, wherein the OHT vehicle includes a gripping member configured to grip and hold a carrier, and a receiver configured to receive a signal. The signal is transmitted to the receiver of the OHT vehicle. The OHT vehicle is moved toward the carrier, and the carrier is gripped by the gripping member of the OHT vehicle. A lifting force is determined based on a weight of a carrier, a number of workpieces in the carrier, or a vertical distance between the OHT vehicle and the carrier, and the lifting force is applied to the carrier.