This disclosure generally relates to systems and methods for tracking the locations of a movable target object (e.g., a robotic arm or other electro-mechanical machine that is guided by a computer program) as it moves relative to a workpiece or part.
Applications involving manufacturing processes that use crawler vehicles or other computer-controlled electro-mechanical machines often employ location tracking in a reference coordinate system. Absolute motion tracking refers to tracking of position and/or orientation defined in a reference coordinate system, such as an airplane coordinate system.
Pointing instruments that can highlight a position or region on a target object, in the local coordinate system of that object, can provide valuable point-of-use information for applications in areas such as automated manufacturing. For example, a Local Positioning System (LPS) of the type disclosed in U.S. Pat. No. 7,859,655 (the disclosure of which is incorporated by reference herein in its entirety) permits an operator to acquire local coordinate measurement and imaging data for an object in the field of view of the physical hardware of the LPS. An LPS may use a pan-tilt unit to orient a camera in the direction of a target object for which local coordinates are needed. A laser range meter can be used to measure range to the object, or distances can be entered or derived algorithmically. Image data, measured range data, and pan-tilt angles are used along with known calibration points to determine the location of the LPS device relative to the target object. With the relative location known, LPS measurements are converted into the local coordinates of the target object's coordinate system (such as airplane or building coordinates). An operator may control the pan-tilt unit, laser range meter, camera devices and other software operations of an LPS using keyboard controls, or interface devices such as joysticks, gamepad controllers, mouse devices, etc. The LPS includes a computer system physically attached to, and collocated with, other components of the LPS.
The LPS disclosed in U.S. Pat. No. 7,859,655 uses known 3-D points on a target object to perform an instrument-to-target calibration, after which the system can be used to make measurements of other points or groups of points in the coordinate system of the target object. This approach for calibration works well if accurate 3-D point data is available for the target object; but in many potential use cases it is not, which mean this mode of LPS operation cannot be used. Since the foregoing LPS process requires knowledge of 3-D data in the work environment, its use as a general-purpose measurement device is limited to those cases where 3-D data is available.
Other processes for general-purpose measurement without use of known 3-D reference data may involve: simple measurement tools, such as tape measures, measuring wheels, GPS or differential GPS, laser trackers, and surveying equipment like theodolites and Total Stations. Some of these solutions can only measure point-to-point differences, and others can measure displacement vectors, but they are not configured to provide both position and orientation for objects that have been moved. Other tracking systems, such as optical motion capture, can measure both position and orientation of one or more objects as those objects move, but motion capture systems require setup of multiple cameras in the tracking environment, which increases complexity and cost, and reduces the portability of the system.
Other special-purpose devices may have some alignment capabilities, but they are not set up for general-purpose usage. For example, machine tools like Coordinate Measuring Machines (CMMs) have internal processes that perform similar tasks for alignment of the tool within the machine workspace.
It would be advantageous to provide a process that addresses LPS use cases for situations where known 3-D points are not available for calibration.