Joint Torque Determination in Articulated Industrial Robots
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Solution Overview
Problem
Current methods for supervising joint torques in articulated industrial robots require additional sensors, increasing costs and potential technical failures, while existing solutions for safety-rated torque supervision often rely on dedicated torque sensors or complex mechanical designs.
Innovation Solution
A method utilizing two sources of joint torque information, derived from dynamic motion planning and measured motor currents, compares the overall current fed to a three-phase alternating current motor with the measured currents of two phases to verify torque reliability without needing dedicated torque sensors, ensuring safety performance level PL d as required by ISO 10218-1:2011.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional torque sensors are used to measure joint torques, then torque measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The motor serves dual purposes: it both drives the joint and provides torque measurement through its existing current sensors. The control device calculates actual torque from measured motor currents, eliminating the need for separate torque sensors. This self-service approach allows the motor to provide both actuation and measurement functions.
Solution Approach 2:
The patent replaces mechanical torque sensors with an electrical measurement approach. By measuring motor currents and calculating torque through control algorithms, the system substitutes physical sensing hardware with computational methods based on electrical parameters already available in the motor control system.
2Reliability
If torque is limited to ensure safety, then safety performance is improved, but robot productivity decreases
Solution Approach 1:
The system dynamically adjusts torque limits based on operational context rather than applying static restrictions. By continuously monitoring actual torque through current measurements and comparing with desired torque from motion planning, the system can enforce safety limits while allowing maximum performance when safe, thus maintaining productivity.
Solution Approach 2:
The control device implements continuous feedback by comparing actual torque (from current measurements) with desired torque (from motion planning). This feedback mechanism enables real-time safety verification without permanently limiting robot capability, allowing the system to operate at full performance within safe boundaries.
Data Source
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AI summary
Method of determining a joint torque in a joint (1) of an articulated industrial robot (2), said robot having a first arm (4) and a second arm (6) which are coupled to each other by said joint (1) and which are movable relative to each other by an electric drive unit (8) coupled to said first (4) and second arm (6), wherein said electric drive unit (8) is controlled by an electronic control device (10) and wherein a measuring device (12) is assigned to said electric drive unit (8) which measures the electric current supplied to the drive unit (8), characterized in that an actual value of the torque (TA) which is applied to said second arm (6) is determined from said measured electric current( IU, IV) and that said electronic control device (10) compares said determined actual torque value (TA) with a predetermined desired torque value (TD) for said joint (1).