Method and apparatus for improving measurement accuracy of a portable coordinate measurement machine

Abstract

A method for improving the measurement accuracy of a portable coordinate measurement machine which comprises an articulated arm having jointed arm segments is presented. This method includes sensing deformation of a portion of the articulated arm when the arm is placed under a load, this deformation causing an error in the measurement made by the CMM, and correcting such error in response to the sensed deformation.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]The present application is a reissue of U.S. Pat. No. 6,957,496 issued Oct. 25, 2005. U.S. Pat. No. 6,957,496 was filed as application Ser. No. 10 / 641,670 on Aug. 15, 2003, and was a continuation-in-part of application Ser. No. 10 / 366,589 filed Feb. 13, 2003(now issued as U.S. Pat. No. 7,069,664). This application claims the benefit of provisional application Nos. 60 / 357,599 filed Feb. 14, 2002 and 60 / 394,908 filed Jul. 10, 2002, all of the contents of both provisional applications being incorporated herein by reference and is a continuation-in-part of application Ser. No. 10 / 366,589 filed Feb. 13, 2003 .BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates in general to coordinate measurement machines (CMMs) and in particular to portable CMMs having an articulated arm.[0004]2. Prior Art[0005]Currently, portable articulated arms are provided as a measurement system with a host computer and applications softw...

AI Technical Summary

Benefits of technology

[0011]In accordance with the present invention, a portable CMM comprises an articulated arm having jointed arm segments. In one embodiment, the arm segments include bearing / encoder cartridges which are attached to each other at predetermined angles using a dual socket joint. Each cartridge contains at least one, and preferably two, preloaded bearing assemblies and an encoder, preferably an optical encoder, all assembled in a cylindrical housing. Preferably, two or more encoder read heads are used in each joint so as to cause cancellation effects that can be averaged. The arm segments may be threadably interconnected with the arm tapering from a wider diameter at its base to a narrower diameter at the probe end.

[0012]In accordance with another embodiment of the present invention, one or more of the jointed arm segments of the articulated arm includes replaceable protective coverings and / or bumpers to limit high impact shock and abrasion as well as to provide an ergonomically and aesthetically pleasing gripping location.

[0014]In still another embodiment of this invention, the articulated arm includes a measurement probe at one end thereof. This measurement probe has an integrally mounted touch trigger probe which is easily convertible to a conventional hard probe. The measurement probe also includes improved switches and a measurement indicator light. In one embodiment, the switches have an arcuate, oblong shape and are easily arctuatable by the operator. The improved switches include differing color, surface texture and / or height which allow the operator to easily distinguish between them while the indicator light preferably is color-coded for ease of operation.

[0015]Another embodiment of the present invention includes an articulated arm having an integral, on-board power supply recharger unit. This power supply / recharger unit allows for a fully portable CMM and makes it far easier to use the CMM at a remote location and / or without the need for a directly cabled articulated arm.

[0016]Still another embodiment of the present invention includes an articulated arm having a measurement probe at one end. The measurement probe includes a rotatable handle cover and switch assembly which surrounds the measurement probe. The rotatable handle cover and switch assembly allows the measurement probe to be more easily held and activated regardless of hand position. The use of the rotatable handle cover further precludes the necessity for having a third axis of rotation at the probe end thus allowing for a lower cost and more easily constructed portable CMM (relative to 7 axis CMMs or CMMs having a third angle of rotation at the measurement probe).

Problems solved by technology

The controller mounted to the arm is used to run the executable program but cannot be used to create executable programs or modify executable programs.

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