VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 1

NCMS CTMA Symposium – Detroit

11:30 amWednesday, April 1, 2009

Jim DallamMAG Cincinnati

Tel: +1 859 534 4619

Volumetric Accuracy for Large Machine Tools

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 2

The Continuing Challenge to Manufacture Interchangeable Parts

In the early 1800’s before the Civil War, the challenge was to make military rifles with parts that could be swapped. After that war, the “American System of Manufacture” with precision interchangeable parts enabled making complex merchandise like sewing machines and typewriters.

Today the challenge is to make the much larger parts for planes,ships, and tanks, to equal levels of repeatable precision. Laser interferometry methods are typically used to determine machine compensations. These methods improve machine accuracy, but require multiple setups by highly trained and experienced technicians, are time consuming, and account for significant lost revenue.

A better method is needed.

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 3

Project Objective

Establish a new method to improve the Volumetric Accuracy for Large Machine Tools (VALMT) via a collaborative project during the eighteen months from January 2008 to July 2009.

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 4

Different Machines Present a DifferentKinematic Axis Stack-Up from Part to Tool

MAG U5-1500- Part- Base- Linear X- Linear Y- Linear Z- Rotary C- Rotary A- Spindle/Tool

FOGS SU-16- Part- Rotary W- Base- Linear X- Linear Y- Linear Z- Rotary C- Rotary A- Spindle/Tool

MAG H5-1000- Part- Rotary B- Linear Z- Base- Linear X- Linear Y- Rotary A- Spindle/Tool

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 5

• Advance software previously developed to a productionready commercial product available for use on large five-axismachines equipped with the Siemens 840D controller.

• Test the calibration and compensation methods using pathpositioning and cutting tests.

• Investigate the feasibility and complexity of a “black-box”solution that could be retrofit to legacy machine tools.

Project Tasks

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 6

• The National Center for Manufacturing Science – Ann Arbor, MI• Boeing Research & Technology – St. Louis, MO• Automated Precision, Inc. – Rockville, MD• MAG Cincinnati – Hebron, KY• Siemens Energy & Automation, Inc. – Mason, OH• Warner Robins Air Logistics Center – Warner Robins, GA• Naval Foundry & Propeller Center – Philadelphia, PA• Fleet Readiness Center East – Cherry Point, NC• Anniston Army Depot – Anniston, AL

Project Partners

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 7

API’s T3 Laser Tracker and Active Target

Stationary Stationary T3 Laser Tracker T3 Laser Tracker (with Pan & Tilt)(with Pan & Tilt)

Moving Moving Active Target (AT)Active Target (AT)

““Beam LockBeam Lock””

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 8

API’s T3 Laser Tracker and Active Target (AT)

Small size, portable, large measurable volumeSuper long-term dimensional and thermal stabilityTypical accuracy 5 -10 times better than machine accuracy requirementAT fully autonomous control with 8 hour battery Unlimited AZ and 140 deg EL Pivot accuracy better than 5 microns

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 9

Boeing’s Approach for Volumetric Error Compensation

The approach consists of a laser tracker and spindle-mounted active target. The tracker and active target interact to maintain a metrology ‘beam-lock’ as the machine tool is positioned to a cloud of points within its work envelope. For each point, the actual location (as determined by the metrology) is contrasted with the commanded (desired) location to develop the point compensation values. Software automation then determines the volumetric compensations using a polynomial-equation-based, kinematic-error-model of the machine, and transfers them into the machine tool controller. After this calibration, when the production machine is commanded to a desired location, the volumetric compensations are automatically applied during the move to improve the path and actual location.

T3 Laser Tracker

Active Target

Point Cloud

Short Tool PointsTool Axis

“Beam Lock”

Long Tool Points

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 10

Optimization and Real-Time Compensation Software

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 11

Siemens’ Sinumerik 840D “Open Architecture” CNC

The VALMT project utilizes Sinumerik’s Open Architecture “Compile Cycle” technology. This integrates the polynomial-equation-based, kinematic-error-model into the real-time CNC path control algorithms.

Siemens CNC Base System

Siemens VCi Interface CC

VALMT Real Time Algorithms

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 12

Siemens’ Sinumerik 840D “Open Architecture” CNC with VALMT Compile Cycle

The compile cycle computes the volumetric compensations at the interpolation level of the CNC. When the controller calculates the path trajectory, it breaks the motion block into discrete points evenly spaced in time that are then fed into the servo loop of each axis. Below we see a typical acceleration, constant velocity, deceleration, and stop characteristic of a move. Each of these points is fed into the VALMT compile cycle algorithm for compensation. Each time slice is treated as a pose of the machine, and compensations are computed for all of the servo commands for that time slice to correct machine location and orientation. The algorithm takes about 100us to execute, well within the real time constraints of the system.

Time

Dis

tanc

e

Example path interpolation

output from the CNC

Interpolation output with

compensations from VALMT

Compile Cycle.

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MAG is a leading large machine tool builder with a global service and maintenance organization

MAG will commercialize this volumetric compensation methodology in parallel with API.

Mac

hine

s an

d eq

uipm

ent

Heads, BlocksCams, CranksTransmissions

ChassisComposite Panels

Engine Components

Pumps, ValvesCompressors

Molds Machinery Components

Large StructuresApp

licat

ions Titanium Components

Aluminum ComponentsComposite StructuresEngines Components

Landing Gear

Large FramesBearingsCases

Planetary CarriersLift Arms

Wheels, Axles,Brake Disks

Chassis ComponentsEngines and

Transmissions

Thin Film Solar PanelsGear Case Assemblies

HubsPlanetary Carriers

BearingsShafts, Blades

FTV??

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Project Testing on Different 5-Axis Machines and Verification at Depot Sites

VALMT – Volumetric Accuracy for Large Machine Tools Date: 01-APR-2009 15

Comparison of Error Mapping Technologies

Calibration method

3-D Grid

Sequential laser linear setups & measurements

Instrument used

Laser Tracker

1D Laser + Optics

6D Laser + Optics1D Laser

Tracer + Cat’s eye

VALMTpolynomial equation

solution for all positions and poses

Laser Tracker

+ Active Target

Linear Axes limitations

3 Axes

3 Axes

Rotary Axes limitations

N/A or separate test

Not limited, fully exercised

N/A or separate test

Measurementtime

<2 hours

1-2 days

2-4 days

Verificationmethod

At any arbitrary positions

and posesin the

work space

Measure diagonals

1-2 days depends on grid density

Measure diagonals

3 Axes N/A or separate test

3 Axes N/A or separate test < 4 hours

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Before and After Accuracy Graphs

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Afte

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Bef

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All machines showed volumetric compensation improved static positioning accuracy.All machines could be compensated to better than three times the process repeatability.

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Advantages of This VALMT Approach

Complete Volumetric Calibration – Measurements are taken within the full volumetric work envelope of the machine combining serial kinematic errors and geometric effects not possible with current axis-by-axis methods.

Practical Metrology Methods – Measurements are automated within a single coordinate system using laser tracker technology that has proven to be a simple metrology tool that does not require extensive training to use.

Rapid Calibration Time – Calibration is performed in a single setup with automated measurement of hundreds of points completed in just a few hours compared to alternate methods that can take days or weeks.

Easy to Extend – The model readily extends to arbitrary serial kinematic structures, a key advantage over alternate methods.

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Follow-up Points-of-Contact

• The National Center for Manufacturing Science – Ann Arbor, MITony Haynes, tel: 734 995 4930

• Boeing Research & Technology – St. Louis, MOPhil Freeman, tel: +1 314 234 4050

• Automated Precision, Inc. – Rockville, MDDave Maxham, tel: +1 240 268 0400

• MAG Cincinnati – Hebron, KYJim Dallam, tel: +1 859 534 4619

• Siemens Energy and Automation, Inc. – Mason, OHRoger Hart, tel: +1 513 218 1626