AACMM Arm Segments with Dual-Layer Sleeve for Thermal Stability
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Solution Overview
Problem
Portable articulated arm coordinate measuring machines (AACMMs) face accuracy issues due to arm segment twisting caused by temperature changes, which cannot be effectively mitigated by internal temperature sensors, leading to angle errors in measurement.
Innovation Solution
The AACMM design incorporates a manually positionable articulated arm with arm segments featuring a tubular core surrounded by an outer sleeve with orthogonally oriented fibers, reducing torsional effects and improving accuracy by minimizing twisting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a patterned composite material is used on the outer region of the arm segment, then the arm segment gains structural properties, but it becomes susceptible to twisting due to temperature changes
Solution Approach 1:
The arm segment uses a composite structure consisting of an inner core made of one material and an outer sleeve made of a different material with different thermal expansion characteristics. This composite construction allows the arm to maintain structural strength while compensating for thermal twisting effects through the differential expansion properties of the two materials.
Solution Approach 2:
The arm segment is divided into two distinct segments: an inner core and an outer sleeve. This segmentation allows each component to be optimized independently - the core provides structural integrity while the sleeve provides thermal compensation, resolving the contradiction between strength and thermal stability.
2Measurement precision
If temperature sensors are placed in the interior of the arm segments, then temperature can be measured, but the sensors cannot effectively mitigate twisting effects
Solution Approach 1:
The outer sleeve acts as an intermediary element between the inner core and the external environment. It provides thermal compensation by expanding or contracting in response to temperature changes, thereby protecting the inner core and encoder from thermal twisting effects without requiring direct temperature measurement or active control.
3Strength
If the outer sleeve is fully coupled to the core, then structural integrity is maximized, but torsional effects are increased
Solution Approach 1:
The coupling between the outer sleeve and inner core is made local rather than continuous. By providing discrete coupling points or limited contact areas, the design maintains structural integrity at critical locations while allowing the sleeve to move independently in other regions, thereby reducing torsional effects and improving thermal compensation.
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
The solution effectively minimizes twisting of arm segments in response to temperature changes, enhancing the accuracy of measurements by reducing torque on encoders, thereby improving the overall performance of the AACMM.
Implementation Method 1
The outer sleeve is a cylindrical tube having a first portion at a first end and a second portion that extends from the first portion to an opposite end. The first portion is coupled to an end of the core. The first portion is shorter than the second portion and the second portion is configured to move relative to the core.
Implementation Method 2
Arm portions of AACMMs may be susceptible to twist due to temperature changes.
Data Source
AI summary
A portable articulated arm coordinate measuring machine (AACMM) is provided including a manually positionable articulated arm having opposed first and second ends. The arm includes multiple connected arm segments. Each arm segment has a longitudinal axis. Each arm segment includes a generally tubular core, an outer sleeve surrounding at least a portion of a length of the core, and at least one position transducer for producing a position signal. The outer sleeve is a cylindrical tube having a first portion at a first end and a second portion that extends from the first portion to an opposite end. The first portion is coupled to an end of the core. The first portion is shorter than the second portion and the second portion is configured to move relative to the core.