Horizontal 4-Axis Robot Load Center of Gravity Estimation
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Solution Overview
Problem
Conventional techniques for estimating the position of the center of gravity of a load on a horizontal 4-axis robot arm are inadequate, as they cannot change the state where the force of gravity acts on the workpiece, unlike vertical 6-axis robots.
Innovation Solution
An apparatus and method that utilize a robot arm with four axes, including acceleration and torque acquiring units to calculate inertia at different angles of the fourth axis, allowing for the estimation of the center of gravity on a plane perpendicular to the robot's base, even with irregularly shaped or dense loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional center of gravity estimation techniques are used, then the estimation can be performed on vertical 6-axis robots, but the technique cannot be applied to horizontal 4-axis robots due to inability to change gravity state
Solution Approach 1:
The patent changes the parameter being measured from gravity-based force (vertical axis) to inertia-based acceleration (horizontal axis). By measuring acceleration during movements at different fourth-axis angles and calculating inertia, the system achieves center of gravity estimation on horizontal 4-axis robots where gravity state cannot be changed, thus resolving the adaptability issue while maintaining estimation reliability
Solution Approach 2:
The patent replaces the gravity-based measurement mechanism (vertical 6-axis robot using fifth axis to change gravity state) with an inertia-based measurement mechanism (horizontal 4-axis robot using acceleration and torque sensors). This substitution allows center of gravity estimation on horizontal robots by measuring acceleration during controlled movements and calculating inertia, thereby achieving both adaptability and reliability
2Measurement precision
If multiple operation periods with different fourth-axis angles are used, then center of gravity estimation accuracy is improved, but measurement time increases
Solution Approach 1:
The patent performs measurements at three different fourth-axis angles (0°, 90°, -90°), which provides sufficient accuracy for center of gravity estimation. This partial action approach achieves the necessary measurement precision without requiring exhaustive measurement at all possible angles, thus balancing accuracy with time 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
Enables precise and reliable estimation of the center of gravity, improving arm control by reflecting this information in the robot's operations, even with loads of indefinite shapes or irregular densities.
Implementation Method 1
a first acceleration acquiring unit configured to acquire acceleration generated at the second axis during accelerated and decelerated intervals
Implementation Method 2
a first torque accruing unit configured to acquire acceleration torque generated at the fourth axis during the accelerated interval and deceleration torque generated at the fourth axis during the decelerated interval
Implementation Method 3
a first inertia calculating unit configured to calculate inertia τI4a generated around the fourth axis based on the acceleration in both the accelerated and decelerated intervals, the acceleration torque and the decelerated torque
Data Source
AI summary
A position of gravity of center of a load loaded to an industrial load is estimated. The robot has a robot arm driven horizontally. The robot arm includes first to fourth axis. Acceleration generated at the second axis during accelerated and decelerated intervals of each of three operation periods. In each operation period, the second axis is driven to move the robot arm from one initial position to one first estimating position and returns it from the estimating position to the initial position. During each operation period, the load is given a known mass, the fourth axis is positioned at a preset angle, and the first, third and fourth axes are the same in positions between the initial and estimating positions. The fourth-axis position is changed to different angles for every operation period. Based on calculated acceleration and known factors of the robot and load, the position is estimated.