Rotary Encoder Spiral Track Multi-Rotation Position Sensing
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Solution Overview
Problem
Existing rotary encoders can only detect relative position or absolute position within a 360° range, which is insufficient for applications requiring measurement of multiple rotations, such as robotics, where knowing the number of whole revolutions is crucial to prevent over-rotation and ensure accurate resetting of robot joints.
Innovation Solution
A device with a follower constrained to move on a spiral or helical track, combined with magnetic sensors, allows for absolute determination of relative rotational position over multiple rotations by converting relative rotation into linear motion and using a mechanical encoder to detect the radial position of the follower, enabling direct measurement of whole rotations without needing to rotate the shaft to its limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional magnetic sensors or optical sensors are used to detect rotational position, then relative position or absolute position within 360° can be sensed, but the number of whole revolutions cannot be measured
Solution Approach 1:
The invention adds a temporal dimension to the position measurement by tracking when the follower passes through the transition zone between circular arcs. By recording the time of transition events and counting them, the system accumulates revolution information beyond the 360° range, converting a 2D position problem into a 3D solution that includes temporal accumulation data.
Solution Approach 2:
The spiral track design allows the follower to continuously accumulate rotational information as the shaft rotates. The transition zones are strategically positioned to occur at regular angular intervals, creating continuous counting opportunities that accumulate revolution data without interruption over multiple rotations.
2Measurement precision
If calibration is performed by rotating the shaft to its limit position, then absolute position can be determined, but the shaft may be damaged and the process is complex
Solution Approach 1:
The system performs preliminary actions by pre-positioning the follower in a known reference state at the inner circular arc, and pre-configuring the transition zones to occur at predictable angular positions. This allows absolute position to be determined without requiring the shaft to be rotated to its mechanical limit, eliminating the need for potentially damaging calibration procedures.
Solution Approach 2:
The transition zones act as intermediary markers that bridge the gap between relative position sensing and absolute position determination. Instead of requiring direct measurement at the shaft's mechanical limit, the transition zones provide intermediate reference points that enable absolute position calculation through temporal counting and angular relationship analysis.
3Measurement precision
If multiple sensors are used to detect magnetic transitions for multi-bit accuracy, then position measurement precision improves, but device complexity increases
Solution Approach 1:
The invention replaces complex multi-sensor magnetic or optical detection systems with a single follower that mechanically tracks the spiral track. The position information is encoded in the geometry of the spiral track and the temporal sequence of transition zone passages, eliminating the need for multiple sensors and their associated complexity while maintaining or improving measurement precision.
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
Enables direct and precise measurement of absolute rotational position over multiple rotations, eliminating the need to calibrate by rotating the shaft to its limit, thus avoiding potential damage and simplifying the resetting process.
Implementation Method 1
A sensor interacts with the ring, and is located so that the magnetic poles move past the sensor as the rotation that is desired to be sensed takes place. The sensor detects changes in magnetic polarity as the poles move past the sensor.
Implementation Method 2
a follower constrained to move on a first track fast with the first part and on a second track fast with the second part, the first track being linear and the second track comprising a plurality of circular arcs and at least one transition section connecting one of the circular arcs to another, the tracks being arranged so as to convert relative rotation of the parts into linear motion of the follower.
Data Source
AI summary
A device for sensing the relative rotary position of first and second parts about a rotation axis, the device comprising a follower constrained to move on a first track fast with the first part and on a second track fast with the second part, the first track being linear and the second track comprising a plurality of circular arcs and at least one transition section connecting one of the circular arcs to another, the tracks being arranged so as to convert relative rotation of the parts into linear motion of the follower, wherein the second track is generally spiral, each circular arc is of constant radius about the rotation axis and the first track is perpendicular to the rotation axis.