Automated Warehouse Access Safety Using Vehicle Watchdog Timers
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Solution Overview
Problem
Automated warehouses with shuttle and satellite systems face challenges in ensuring human safety during operator intervention due to incomplete wireless communication coverage, leading to potential vehicle operation risks when accessing the warehouse, as current safety-certified transmission systems are costly and technically limiting.
Innovation Solution
Implementing a safety-certified watchdog timer system on control units of shuttle and satellite vehicles, which uses check signals and counters to detect communication interruptions, triggering de-energization and ensuring vehicles are in safe mode through safety contactors, even without secure wireless communication, by disconnecting power via safety-certified circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If safety-certified wireless transmission networks are implemented to ensure human safety during operator intervention, then safety reliability is improved, but system cost and device complexity increase significantly
Solution Approach 1:
The patent introduces a safety controller as an intermediary component that receives signals from both the access control system and vehicle control systems. This mediator coordinates safety operations, ensuring that when an operator accesses the warehouse, all vehicles are properly de-energized through a centralized control mechanism rather than requiring complex wireless safety networks throughout the entire system.
Solution Approach 2:
The patent extracts the safety-critical functions from the general wireless transmission system and implements them through dedicated hardwired circuits and safety contactors. By separating safety functions from the main control system and using independent safety circuits, the patent achieves safety certification without requiring comprehensive safety-certified wireless coverage throughout the warehouse.
2Reliability
If comprehensive safety-certified wireless transmission networks are deployed to cover all warehouse points, then communication reliability is improved, but installation cost and system complexity increase
Solution Approach 1:
The patent applies safety-certified communication only where absolutely necessary - specifically at the access control point and in direct vehicle control circuits. Rather than implementing safety certification throughout the entire wireless network, the solution focuses safety measures locally at critical interfaces where operator interaction occurs, thereby reducing overall system cost while maintaining essential safety functions.
3Adaptability or versatility
If wireless communication is used for vehicle control to enable flexible operations, then operational flexibility is improved, but safety certainty during operator access deteriorates due to potential communication interruptions
Solution Approach 1:
The patent implements prior cushioning by using watchdog timers that continuously monitor wireless communication between vehicles and the safety controller. These timers are pre-configured with timeout thresholds that trigger de-energization commands if communication is lost, providing a safety buffer that compensates for potential wireless communication interruptions before they can compromise operator safety.
Solution Approach 2:
The patent establishes feedback mechanisms where vehicles continuously report their status and position to the safety controller through wireless communication, and the safety controller provides continuous monitoring. This feedback loop enables the system to detect communication interruptions and respond by triggering safety protocols, thereby maintaining safety certainty despite the use of flexible wireless communication for normal operations.
Data Source
AI summary
An automated warehouse has a main path, secondary paths, a main vehicle movable along the main path, one or more auxiliary vehicles movable along the secondary paths, and an access point. On each vehicle a wireless device receiving and sending wireless signals and a control unit associated with safety modules including a safety-certified watchdog timer and a counter are installed. The wireless devices send check signals containing the value of the counter of the respective vehicle to the access point, which sends signals in response to received check signals When a response signal is received from a wireless device, the respective counter is incremented and the associated watchdog timer starts to measure time when the value of the counter differs from the value received via check signals. Each control unit de-energizes the respective vehicle when a time longer than a predetermined time is detected via the watchdog timer.