Structural Design of a Newly Developed Ultraprecision machine Tool “ANGEL”(Reprint from Proceedigns of ISUPEN2011)

Hayato Yoshioka1 , and Hidenori Shinno1
1

Tokyo Institute of Technology, Yokohama, Japan

Abstract – Demands for fabricating micro- and nano-structured surfaces have rapidly increased in the advanced science andengineering fields. In order to meet such requirements it is necessary to develop an ultraprecision machine tool with both
nanometer-level machining accuracy and a large machining area. This paper presents a newly developed ultraprecision machine toolfor enabling nano-machining over large work area. In order to remove the principal error factors caused by machine structure, themachine tool developed employed a perfect non-contact structure excluding the machining point. In addition main components of thesystem were arranged symmetrically to eliminate thermal and dynamic error factors. The performance evaluation results confirm thatthe developed system provides superior performances for nano-machining.
Key Words: Machine tool, Ultraprecision machining, Design concept, Structural configuration

1. Introduction

Precision components

MinimizedAbbe offset

Demands for ultraprecision machining process have increasedin the advanced science and industrial fields [1-3]. In particular,

Noncontact structure

Isolation ofvibration

Minimization oferror sources

Compensation oferrors

Isolation oferror sources

Stable machine
tool structure

Control oferror sources

ultraprecision machine tool with both nanometer order machining

Shut off heat flow

StructuraldesignActive vibration control

accuracy and a large work area. In our research project, therefore,

Symmetricstructre

an ultraprecision machine tool is newly developed forHigh rigid structure

structured surfaces with micro- and nano-patterns have recently
been required for various industrial sectors. In order to meet theEnclosure

requirements, it is necessary and indispensable to realize annano-machining over large work area. The developed machine
tool is composed of some originally designed structural

Thermaldeformation
control

Low center of gravity
Application ofnew structural materials

Fig. 1 Design concept for the stable machine tool structurecomponents such as an X-Y planar positioning table and a Z
vertical positioning stage [4-7]. This paper describes the basic
concept of ultraprecision machine tool and the structuralcomponents. In addition, typical examples of performance
evaluation are also described.
2. Design concept of the developed machine tool
Figure 1 shows a basic design concept for a thermally anddynamically stable machine tool structure. In order to realize astablemachinetoolstructure,

thermalandmechanicaldisturbances from within and without should be considered.
Furthermore, it is important to minimize, isolate, and control
principal error sources for eliminating influence on performanceFig. 2 Structural design of the developed ultraprecision machine tool

effectively. In particular, these design concepts are indispensable
to ultraprecision machine tools with a large working area.

arranged so that a cross point of their measuring axes agrees with

Figure 2 shows a structural design concept of a newly

the machining point to minimize Abbe error including feedback

developed ultraprecision machine tool. It is design to do

position. Principal structural parts, e.g., a main bed, columns,

nano-machining over a large work area, and it is consequently

beams, and moving bodies are made of low thermal expansion

named “Advanced Nano-pattern GEnerator with Large work areamaterial. All the positioning mechanisms with nano-positioning(ANGEL).” ANGEL is basically a vertical type machining center,capability are supported and driven in a perfect noncontact

and has an X-Y planar positioning table for workpiece motion andcondition.

a Z vertical positioning stage for tool motion.

temperature-controlled enclosure and is supported by an active

Theentiresystem

isinstalledinaThe whole machine structure is symmetrically designed withvibration isolation system to isolate external thermal and dynamicrespect to the vertical center axis (Z axis). Therefore a machining

disturbance. In addition, to isolate internal vibration disturbancepoint is located at the structural center of the entire system.

the system has two of frames; a structural frame with driving

Furthermore feedback sensors for all positioning mechanisms arecomponents and a metrology frame with measuring components.

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(a) Overall

Fig. 3 Structural configuration of ANGEL
Table 1 Specifications of ANGEL(b) Machining point
Fig. 4 Exterior appearance of ANGELIn consequence, various nonlinear phenomena such as friction
and stick slip can be removed from machine structure, and error
factors in the overall system can be minimized.
As mentioned above, ANGEL can be summarized by thefollowing attributes:

3.2 X-Y planar positioning table
The X-Y planar positioning table of ANGEL is driven by
hybrid linear motors to realize both nano-positioning and longrange motion. Fig. 5 shows the structural configuration of thedeveloped X-Y table. The moving table is driven by eight voice(1) Symmetrically designed structure,coil motors (VCM) arranged around the table in both the X and Y(2) Abbe error offset-minimized structure,

directions. Although VCM can generate quick and accurate(3) Motion error-minimized structure,driving force, its effective stroke is limited by size of permanent(4) Thermal deformation-minimized structure,magnets. In order to realize a large working area, shaft type linear(5) X-Y planar positioning table with large work area,

motors which have long stroke over several hundred millimeters(6) Z vertical positioning stage with gravity compensation,

are installed into the driving system with two stacking rectangular(7) Air turbine-driven aerostatic spindle system.

frames. In this mechanism the shaft type linear motors drive a coilof VCM independently of a main feedback loop so as to keep a

3. Structural configuration of the developed machine tool

relative distance within a stroke of VCM. In consequence, the3.1 Machine structurenano-motion control system of the moving table drives the VCM

The structural configuration of the developed machine tool

without considering the stroke of the VCM.

ANGEL is shown in Fig. 3. The main body of ANGEL consists ofThe square moving table is levitated by five porous aerostatica large flat bed, two of columns, and two of top beams. An X-Ybearings which are preloaded by vacuum attraction force. Eightplanar positioning table and a Z vertical positioning stage are also

VCMs are symmetrically arranged around the square moving

installed in the main structure. The fundamental structural

table so as to drive the center of gravity of the moving table inmodules such as the main bed, columns, top beams, andboth the X and Y directions. The moving table on the flat base ispositioning systems are made of alumina ceramics (Al2O3)

supported and driven in a non-contact condition. The rectangularbecause of its low thermal expansion coefficient, high Young’sframe structure with the VCM coils and the relative displacement

modulus, and low density.

sensor are driven by the shaft type linear motors.

Figure 4 shows appearance of the developed machine tool

The table position in both the X and Y directions can beANGEL. The overall system is mounted on a pneumatic typemeasured using a laser interferometer fixed on the flat bed. The

active vibration isolation system and is installed into theintersection point of the laser beams for the X and Y measurement

temperature-controlled enclosure within 23±0.2 degrees Celsius.

is allocated at the machining point to minimize the Abbe's error.

Table 1 shows the basic specifications of the ANGEL. The massof the whole system is relatively light because most ofcomponents are made of ceramics.

3.3 Z vertical positioning stage
In order to achieve vertical nano-motion control, it is one of themost important issues to support gravity load of the moving part.
Counter mass and counter balance mechanisms with pneumatic

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2Fig. 5 Structural configuration of the X-Y planar positioning table

Fig. 6 Structural configuration of the Z vertical positioning stage

cylinder are generally used for gravity compensation in

4. Performance evaluation

conventional machine tool structure, while use of those

In order to evaluate the performance of ANGEL, somemechanisms deteriorates the performance due to vibration, lowpositioning experiments were performed under a free load

response or pressure fluctuation. By contrast, pressure fluctuation

condition. Figure 7 shows a 1nm stepwise positioning of the X-Y

in vacuum cylinder during piston movement is significantly lower

planar positioning table and the Z vertical positioning stage. The

than that in pneumatic cylinder because the absolute pressure in

X-Y table and the Z stage are supported and driven in a

vacuum cylinder is negligibly small.

non-contact condition to eliminate nonlinear phenomena such as

Figure 6 shows the structural configuration of the developed Z

friction, stick slip, backlash, etc. In consequence, clear stepwisevertical positioning stage. The moving body with tools is guided

nano-motions in both directions can be observed in all driving

by aerostatic guideways which are vertically allocated in parallelaxes.

and driven at the center of gravity of the moving body by a VCM.

Figure 8 shows a result of circular motion test in the X-Y

A pair of pistons of the developed gravity compensators is fixedplane with a diameter of 100mm and a feed speed of 62.8mm/s.

on the moving stage, and there is small gap between the pistons

There was no quadrant glitch in the obtained circular motion andand vacuum cylinders to remove friction at seal.

the maximum radial error during the driving was less than 4.5nm.

In addition, in order to isolate the excited vibration of the top
beam caused by the reaction force of the VCM, the guideways

From this result a smooth nano-motion can be realized over large
working area by using the hybrid linear motor.

and the laser interferometer of the Z positioning stage wereTo evaluate basic machining capability of ANGEL, someseparately installed on the structural frame and the metrology

cutting experiments were performed. A single crystal diamondframe respectively, as shown in Fig.6.

tool was fixed on the Z vertical stage, while a workpiece ofoxygen free copper was fixed on the X-Y planar positioning table.

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(a) 50nm step heightFig.7 1nm stepwise response of ANGEL(b) 20nm step heightFig.9 SPM images of stepped surface
Acknowledgements
This research project was financially supported by the Japan
Society for Promotion Science (JSPS) Grants-in-Aid for
Scientific Research (A) No.19206017, the Machine Tool
Foundation, and the Electro-Mechanic Technology Advancing
Foundation.

Fig.8 Circular motion test of X-Y planar positioning table

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