Robot Arm Shaft Speed Detection Using Phase-Shifted Hall Sensors
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Solution Overview
Problem
Existing speed detection systems for robot arms using Hall sensors suffer from low resolution and high error in rotational speed measurement due to quantization errors and phase differences in sensor signals, leading to inaccurate speed calculations.
Innovation Solution
A speed detection apparatus is implemented, featuring two Hall sensors with a 90-degree phase difference on the rotational shaft of a robot arm, where the differential signals from these sensors are squared and summed to calculate the rotational speed, improving accuracy and reducing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single Hall sensor is used to detect rotational position, then the device complexity is low, but the measurement precision of rotational speed is poor due to quantization errors
Solution Approach 1:
The patent divides the single sensor detection function into two separate Hall sensors that detect different phase components (sin and cos components) of the rotational position. By segmenting the detection into two orthogonal components, the system achieves more precise speed measurement through vector-based calculation, reducing quantization errors inherent in single-sensor approaches.
Solution Approach 2:
The patent transitions from one-dimensional position detection to two-dimensional detection by using two Hall sensors arranged with 90-degree phase difference. This dimensional expansion allows the system to capture both sin and cos components of the rotational signal, enabling more accurate speed calculation through differential and vector operations.
2Measurement precision
If traditional differentiation methods are used to calculate speed from position signals, then the calculation process is simple, but the speed measurement accuracy is low due to error amplification
Solution Approach 1:
The patent changes the calculation parameters by using differential signals from two phase-shifted sensors instead of directly differentiating a single position signal. The method calculates speed through the formula v = k * sqrt((dθ1/dt)² + (dθ2/dt)²), where the differential operations are performed on both sin and cos components separately, then combined through vector magnitude calculation, which reduces error amplification.
Solution Approach 2:
The patent introduces intermediate differential signals from two Hall sensors as mediators between the raw position detection and the final speed calculation. These intermediate signals (dθ1/dt and dθ2/dt) serve as buffered representations that reduce the direct impact of quantization errors on the final speed measurement.
3Measurement precision
If Hall sensor signals are used directly for speed detection, then the response time is fast, but the measurement precision is poor due to phase differences and quantization errors
Solution Approach 1:
The patent performs preliminary differentiation of the Hall sensor signals to obtain velocity components before combining them through vector calculation. By pre-calculating the differential signals dθ1/dt and dθ2/dt from the two phase-shifted sensors, the system prepares processed data that reduces quantization errors in the final speed computation, achieving both precision and efficiency.
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
This approach enhances the accuracy of rotational speed measurement by approximately 30 times compared to traditional methods, allowing for precise speed control and safe operation of robot arms by preventing motor over-speeding.
Implementation Method 1
A rotation sensor such as a rotary encoder is attached to a motor that drives each shaft of a robot arm
Data Source
AI summary
An speed detection apparatus of a rotational shaft in a robot arm that is applied to a drive mechanism is provided. The speed detection apparatus includes: first and second rotation sensors that are disposed on a side of a rotational shaft of the robot arm and outputs first and second rotational position signals with a phase difference of 90 degrees; first and second differentiators that differentiate the first and second rotational position signals; and a speed calculator that obtains a rotational speed of the robot arm by calculating a sum of squares of a first differential signal and a second differential signal.