Robotic Camera Optical Axis Alignment at Extended Working Distance
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Solution Overview
Problem
Robotic camera systems used in precision surgeries face significant position errors due to misalignment of the camera's optical axis with the robot's motion coordinate frame, especially at extended optical working distances, leading to suboptimal surgical outcomes.
Innovation Solution
An automated method for calibrating the optical axis of a digital camera within a robotic camera system, which generates a homogenous transformation matrix without requiring foreknowledge or modeling of the camera's optics, thereby correcting for any skew or misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the camera is mounted to the robot end-effector for automated machine vision tasks, then the system enables automated surgical assistance with real-time imaging, but position errors occur due to misalignment between the camera's optical axis and the robot's motion coordinate frame
Solution Approach 1:
The patent performs optical axis calibration before automated surgical operations. The system captures reference images of a calibration target at multiple known robot positions, pre-computes transformation matrices that map between the robot coordinate frame and camera optical frame, and stores these for use during automated surgery. This preliminary calibration eliminates position errors during actual surgical tasks.
Solution Approach 2:
The patent introduces a calibration target with known geometry as an intermediary object. This target serves as a mediator between the robot's motion coordinate frame and the camera's optical coordinate frame, enabling the system to compute accurate transformation relationships. The calibration target provides reference points that facilitate precise coordinate system alignment.
2Area of stationary object
If the optical working distance is extended to increase field-of-view, then the camera captures a broader surgical area, but position errors are magnified due to the increased distance
Solution Approach 1:
The patent computes transformation matrices that account for the specific optical working distance. By capturing calibration data at the actual extended working distance used during surgery, the system adapts the coordinate transformation parameters to compensate for the increased distance. This allows the system to maintain position accuracy even when operating at extended optical working distances for broader field-of-view.
3Measurement precision
If a full optical model is created to map optical behavior to robot kinematics, then position accuracy can be improved, but the programming complexity and difficulty of deriving accurate optical models increase significantly
Solution Approach 1:
The patent extracts only the essential calibration parameters needed for coordinate transformation without requiring a complete optical model. Instead of deriving complex optical models involving lens distortion, focal length, and principal point calculations, the system extracts transformation matrices directly from calibration images taken at known robot positions. This extraction approach achieves high position accuracy while avoiding the programming complexity of full optical modeling.
Data Source
AI summary
A method, instructions for which are executed from a computer-readable medium, calibrates a robotic camera system having a digital camera connected to an end-effector of a serial robot. The end-effector and camera move within a robot motion coordinate frame (“robot frame”). The method includes acquiring, using the camera, a reference image of a target object on an image plane having an optical coordinate frame, and receiving input signals, including a depth measurement and joint position signals. Separate roll and pitch offsets are determined of a target point within the reference image with respect to the robot frame while moving the robot. Offsets are also determined with respect to x, y, and z axes of the robot frame while moving the robot through another motion sequence. The offsets are stored in a transformation matrix, which is used to control the robot during subsequent operation of the camera system.