Application of a Force Sensor to Improve the Reliability of Measurement with Articulated Arm Coordinate Measuring Machines

Abstract

A study of the operator contact force influence on the performance of Articulated Arm Coordinate Measuring Machines (AACMMs) is presented in this paper. After developing a sensor capable of measuring the contact force applied by an operator, a ring gauge has been used to analyse the relationship between the contact force and diameter and form errors measured with the AACMM. As a result, contact force has been proved as one of the main factors influencing the AACMM performance. A probe deflection model based on the Finite Element Method (FEM) has been also proposed in order to obtain the AACMM probe deflection caused by contact force. This allows measurement correction by comparing them with reference values, specifically, a ring gauge. Experimental test results show a significant measurement improvement that minimizes diameter error. Finally, an uncertainty evaluation for the contact force sensor and AACMM measurements with and without probe deflection model has been carried out in order to validate the ability of the sensor and the methodology followed.

Dynamic Deformations in Coordinate Measuring Arms Using Virtual Simulation

“…Loads and forces computed by MSC-ADAMS simulations improve the accuracy of FEA by providing better assessment of how they vary throughout a full range of motion and operating environments. The developed virtual model corresponds closely with the available instrument used for the first tests [13,14], which showed that both the type of geometry to measure [8,9] as the human factor [10] had great influence on the quality of measurements. Specifically, the CMA used for the development of the methodology (ROMER Sigma 2048 of Hexagon Metrology©) has a spherical working range of Ø1800 mm, length accuracy specification of ±0.025 mm and uncertainty of ±0.045 mm given by the manufacturer.…”

“…1, right) were monitored for different operators on measurements of planar surfaces and inner cylinders by means of strain gauges assembled on the CMA hard probe [13,14]. Some of the values and directions of the monitored forces will be subsequently introduced to the virtual model in order to use them as valid "seeds" for the dynamic structural deformations survey.…”

“…The application presented here starts from the previous experience of a basic study of measuring force [13,14] as abstracted in Fig. 1.…”

“…However, Vrhovec et al [12] suggest that the error due to the deflection caused by contact forces is one of the most influential and that it can be compensated or at least taken into account for calculating measurement uncertainty. Preliminary studies from this research team have proved that the forces exerted during measurements errors can produce errors up to hundreds of micrometres [13][14][15]. In any case, the contact force and the deflection on the structure are parameters not currently considered in the internal mathematical calculations of the CMA software.…”

Verification of an articulated arm coordinate measuring machine using a laser tracker as reference equipment and an indexed metrology platform

“…They present a virtual circle gauge method composed of two aluminium alloy bar gauges of 1000 mm length with four groups of three conic holes which determine the four virtual circles. The same author in [22] analyzes the influence of the contact force applied by the operator on the performance of AACMMs by means of a contact force sensor and a ring gauge, proposing a probe deflection model to reduce the diameter error. AACMMs are manually operated, fact that allows that a same point could be measured from multiple arm's poses.…”