Medical Support Arm Torque Control Without Joint Torque Sensors
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Solution Overview
Problem
Existing medical support arm systems face challenges in achieving torque control without torque sensors, limiting their ability to respond effectively to various operational situations, particularly in terms of cost-effectiveness and flexibility.
Innovation Solution
A medical support arm system with a multilink structure and a control device that estimates external forces based on actuator drive characteristics, allowing for torque control and joint unit drive management without the need for torque sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If torque sensors are used to achieve torque control, then control accuracy is improved, but device cost and complexity increase
Solution Approach 1:
The patent replaces the mechanical torque sensor with a computational approach using a torque estimation unit. This unit calculates external torque by analyzing the drive characteristic (current, voltage, power) of the actuator and subtracting the reaction force torque (calculated from link weight, gravity, and joint angles). This substitution eliminates the need for physical torque sensors while achieving equivalent torque control accuracy.
Solution Approach 2:
The patent introduces a torque estimation unit as an intermediary computational component that mediates between the actuator drive characteristics and the control system. This unit processes actuator current/voltage data and link parameter data to generate estimated torque values, serving as a virtual intermediary that replaces the need for direct mechanical torque measurement.
2Adaptability or versatility
If torque sensors are installed in each joint unit, then torque control capability is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive mechanical torque sensors with a computational torque estimation system. The torque estimation unit uses readily available actuator drive characteristic data (current, voltage, power) and pre-stored link parameter data to calculate external torque, eliminating the need for costly torque sensor hardware in each joint unit while maintaining torque control capability.
Solution Approach 2:
The system uses its own existing components (actuator drive characteristics and link parameters) to generate torque information without requiring external torque sensors. The torque estimation unit leverages data already present in the control system, making the system self-sufficient for torque control applications.
3Device complexity
If estimated torque values are used for control, then device cost is reduced, but control precision may deteriorate
Solution Approach 1:
The patent implements feedback control using the estimated torque values. The torque estimation unit continuously calculates external torque based on real-time actuator drive characteristics, and the joint control unit uses these feedback values to adjust actuator commands. This closed-loop feedback mechanism ensures that control precision is maintained despite using estimated rather than directly measured torque values.
Solution Approach 2:
The patent replaces direct torque measurement with a computational model that uses actuator drive characteristics (current, voltage, power) and link parameters (mass, center of gravity, moment of inertia) to estimate external torque. This substitution maintains control precision by using accurate physical models and real-time drive data.
Data Source
AI summary
Provided is a medical support arm system including a support arm that is a multilink structure having a plurality of links connected by a joint unit including an actuator, and supports a medical unit. The medical support arm system further includes a control device including an external force estimation unit to estimate an external force acting on the joint unit on the basis of a drive characteristic of the actuator, and a joint control unit to control drive of the joint unit on the basis of an external torque estimated by the external force estimation unit.