Surgical Tool Joint Calibration for Backlash and Compliance Compensation
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Solution Overview
Problem
Challenges arise in the engagement and synchronization of surgical tools with surgical robotic arms, particularly due to the lack of mechanical hardstops, which complicates the attachment and operation of tools, leading to potential equipment malfunctions during surgical procedures.
Innovation Solution
A method and apparatus for engaging the driving motor of the rotary actuator with the instrument's roll tool disk, involving detection of tool attachment, torque threshold monitoring, and synchronization of two motors through a two-stage method to ensure safe and precise coupling, along with mechanisms to account for backlash and compliance, and provide safety enhancements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical hardstops are removed to enable unlimited range of motion, then the instrument's mobility is improved, but the difficulty of detecting and measuring engagement deteriorates
Solution Approach 1:
The patent replaces mechanical hardstop-based engagement detection with an optical sensing system. A light source and photodetector are positioned to detect the presence or absence of a mechanical feature (such as a tab or protrusion) on the instrument that would normally be blocked by a hardstop. This optical substitution allows engagement detection without requiring physical hardstops, thus maintaining unlimited range of motion while enabling reliable engagement detection.
2Power
If two motors are coupled to drive a single instrument, then the power and torque are improved, but the synchronization and control complexity deteriorates
Solution Approach 1:
The patent implements a feedback control system where the positions and velocities of both motors are continuously monitored. The control system compares the actual motor states with desired states and generates corrective torque commands to maintain synchronization. This feedback mechanism enables two motors to work together effectively while automatically compensating for differences in motor characteristics, mechanical backslash, and compliance, thus managing the complexity of dual-motor control.
3Ease of manufacture
If backlash and compliance are present in the mechanical design, then the ease of manufacture is improved, but the manufacturing precision and control accuracy deteriorate
Solution Approach 1:
The patent employs dynamic parameter adjustment in the control system to compensate for backlash and compliance. The controller modifies control parameters such as stiffness gains, damping coefficients, and feedforward compensation values based on the operational state and detected mechanical conditions. This allows the system to maintain high position tracking accuracy despite the presence of mechanical compliance and backlash, without requiring overly rigid or complex mechanical designs.
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
Ensures reliable and safe attachment and operation of surgical tools by detecting mechanical engagement, synchronizing motors, and controlling backlash and compliance, thereby enhancing the precision and safety of surgical robotic systems.
Implementation Method 1
driving the drive disk through the rotary motor
Implementation Method 2
determining whether a measured torque of the rotary motor exceeds a preset torque threshold
Data Source
AI summary
The disclosed embodiments relate to systems and methods for a surgical tool or a surgical robotic system. An end effector of the surgical tool is coupled to a tool driver. An actuator is driven by a motor of the tool driver and configured to drive a degree of freedom of the end effector. One or more processors are configured to receive a position command describing a desired position for the end effector, translate the desired position to a command for a joint associated with the end effector, calculate a compensation term to compensate for a source of hysteresis for backlash and/or compliance, and send a motor command for the motor coupled with the actuator based on the compensation term and the command for the end effector.