Servo Motor Safety Monitor Using Hilbert Transform
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Solution Overview
Problem
Existing servo systems face challenges in ensuring safety without increasing costs or complexity, particularly in detecting abnormal encoder outputs, which can lead to safety failures and increased costs due to the need for redundant encoders or complex feedback control systems.
Innovation Solution
A servo system that includes a safety monitor to compare instruction and feedback values from the encoder, generating a stop signal when abnormal conditions are detected, such as differences outside a predetermined range or exceeding upper limits, to stop the servo motor's torque output, thereby ensuring safety without replacing the encoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant encoders are installed to ensure reliable encoder outputs, then safety and reliability are improved, but installation area, cost, and device complexity increase
Solution Approach 1:
The patent creates a virtual copy of the encoder signal processing path by generating a pseudo-feedback value through mathematical transformation (Hilbert transform) of the actual feedback signal. This virtual encoder copy allows safety monitoring without installing physical redundant encoders, thereby maintaining reliability while reducing device complexity and cost.
Solution Approach 2:
The patent replaces the mechanical/redundant hardware approach (installing duplicate encoders) with a signal processing approach (using Hilbert transform to generate pseudo-feedback). This substitution eliminates the need for additional physical components while achieving the same safety monitoring function.
2Measurement precision
If two independent encoders are installed to verify encoder output correctness, then detection precision is improved, but installation area and initial setting time increase
Solution Approach 1:
Instead of installing a second physical encoder for verification purposes, the patent creates a virtual copy of the feedback signal through Hilbert transform. This allows immediate verification of encoder output correctness without requiring time-consuming installation and calibration of additional hardware.
Solution Approach 2:
The patent performs preliminary signal processing (Hilbert transform) to generate the pseudo-feedback value in advance, enabling immediate safety monitoring and verification without waiting for additional encoder installation and initial setting procedures.
3Reliability
If the safety monitor uses feedback signal for safety determination, then safety monitoring function is achieved, but system complexity increases due to additional monitoring circuits
Solution Approach 1:
The patent replaces complex hardware monitoring circuits with a software-based signal processing approach. By using Hilbert transform to generate pseudo-feedback and comparing it with actual feedback through software algorithms, the system achieves safety monitoring capability while minimizing additional hardware complexity.
Solution Approach 2:
The safety monitor unit is designed to perform multiple functions: it processes the actual feedback signal, generates pseudo-feedback through Hilbert transform, compares both signals, and determines safety status. This multi-functional approach consolidates monitoring capabilities into a single unit rather than requiring separate dedicated circuits for each function.
Data Source
AI summary
A servo driver sets an instruction value for an operation of a servo motor based on an instruction signal from a controller. The servo driver sends the instruction value and a feedback value obtained based on a feedback signal to a safety unit. When at least one of the instruction value and the feedback value sent by the servo driver has an abnormal value, an STO signal is generated and sent to the servo driver. When the STO signal is input to the servo driver, the servo driver stops the supply of electricity to the servo motor.