ARTICLE IN PRESS

Nuclear Instruments and Methods in Physics Research A 541 (2005) 144–149
www.elsevier.com/locate/nima

Design and development of a work robot to place ATLAS SCTmodules onto barrel cylinders
S. Teradaa,, H. Kobayashib, H. Sengokub, Y. Katob, K. Harab, F. Honmac,
Y. Ikegamia, Y. Iwatad, T. Kohrikia, T. Kondoa, I. Nakanoe, R. Takashimaf,
R. Tanakae, N. Ujiiea, Y. Unnoa, S. YasudacaHigh Energy Accelerator Research Organization; KEK, Tsukuba, Ibaraki 305-0801, Japanb
Institute of Physics, University of Tsukuba, Tsukuba 305-8571, Japanc
Miniaturized Automation Division, REPIC Corporation, Futtsu, Chiba 293-0058, JapandDepartment of Physics, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japane
Department of Physics, Okayama University, Okayama 700-8530, Japanf
Kyoto University of Education, Kyoto 612-8522, Japan
Available online 7 March 2005

Abstract
More than 2000 silicon modules need to be placed and fastened on the ATLAS SCT barrel tracker. A semi-automatic
pick-and-place work robot was designed and developed to cope with the module placement for the SCT barrel
assembly. We found that this robot could place modules to a mechanical precision of better than 25 mm.
r 2005 Elsevier B.V. All rights reserved.
PACS: 29.40.Gx; 29.40.Wk; 29.90.+r
Keywords: Silicon strip detector; ATLAS SCT barrel module; Barrel cylinder assembly; Semi-automatic work robot

1. Introduction
The ATLAS [1] detector has a large-scale silicon
strip detector system in order to realize highprecision charged particle tracking. As illustratedin Fig. 1, the barrel part of the SCT [2] silicon strip
Corresponding author. Tel.: +81 29 864 5355;

fax: +81 29 864 2580.
E-mail address: susumu.terada@kek.jp (S. Terada).

tracker consists of four concentric cylinders.
Modularized silicon strip detectors [3] of about
12 cm  6 cm are placed on the cylinders. In total,
2112 modules cover the four cylinder surfaces.
Neighboring modules are overlapped to provide
hermetic coverage. The clearance between themodules at the overlapping region is about 1 mm.
Placement of the thousands of high-precision
silicon modules on the cylinders is a demandingtask. Silicon detectors are so delicate that any part0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.nima.2005.01.051

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S. Terada et al. / Nuclear Instruments and Methods in Physics Research A 541 (2005) 144–149

145m2c5r=

6.4 cm12.8 cm~160 cmSCT Barrel Module

SCT Barrel Cylinder

Fig. 1. Conceptual layout of the SCT barrel tracker.

of the silicon sensor surface and bonded wires
should be kept intact under any circumstances.
Therefore, it is practically impossible to conductthe module placement without using a dedicatedapparatus.
In order to cope with the situation, we designed
and developed a high-precision semi-automatic
work robot. This robot picked up and held thesilicon module by itself then brought it to a
speciﬁed position along a secure trajectory.
The robot must place the modules to a precisionbetter than 30 mm and then fasten them on thecylinders [4].

extension of the module is inserted to the support
clip, which is also bonded on the cylinder surface.
The clip provides an auxiliary support point,
which, together with the bracket, allows themodule to be held ﬁrmly from three points.
The module mounting procedure can be broken
down into the following major steps:

2. Module mounting procedure

1. measure and register the place where themodule is to be placed,
2. pick up and hold the module stored in a modulebox,
3. bring the module to the registered position on
the bracket on the cylinder,
4. fasten the module with a pair of screws to thebracket.

The SCT barrel is made of a light-weighthoneycomb cylinder on which surface the barrel
modules are laid out regularly to cover theinteraction region hermetically. The barrel module
has a pair of positioning holes on the bottom
ceramic extension, which also serves as a coolingfacing. Using these holes, the module is precisely
positioned and ﬁxed with a pair of small screws to
the support bracket, which is bonded on thecylinder surface. The top end of the top ceramic

In Step 1, the robot with empty hands moves tothe location where the module is to be placed. Therobot senses the screw holes of the bracket and thesurface of the cooling pipe using cameras andsensors. It then registers the sensed positions as thedestination to bring the module. By having thisstep we could absorb almost all relevant settingerrors.
Each module is being stored in a metal modulebox. The module inside the metal box is positioned

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146

We repeat these steps cyclically for every module
placement.

3. Requirements

BCA'A

Fig. 2. Typical trajectory of the module placement (A-A0 B-C).

precisely with positioning pins. Therefore in Step2, as long as the metal box is precisely set at a welldeﬁned pick up position near the cylinder, therobot is able to pick up and hold the modulealways in the same manner.
During Step 3 the module is brought on thebracket. The cylinder is carefully set at a proper
rotational angle so the module can be verticallylanded on the bracket. By holding the module
vertically we can avoid a stress on the modulecaused by a gravitational moment. Before landingon the bracket, the top end of the ceramic
extension of the module should be inserted to theopening of the clip. This action requires a delicate
movement as illustrated in Fig 2. The module is
moved upward and forward with some rotationsynchronously.
Finally in Step 4, the robot fastens the modulewith a pair of screws using automatic torquecontrolled screw drivers.

In order to meet the high-spatial resolution
requirement of the silicon detector modules, themodule positioning accuracy is required to be
typically 30 mm. Therefore, naturally the modules
need to be handled with an accuracy of better than
this. Since variations of module dimensions, theprecision of the mounting holes, errors of thebracket position on the cylinder are also comparable to this, the robot should be capable of dealing
with these errors to achieve an overall module
positioning accuracy of 30 mm. Accordingly, thework robot should be operational not only with ahigh precision but also be equipped with appropriate position sensors, monitoring tools andﬂexible adjusters to be able to compensate thesevariations and errors. Furthermore, the robot
should be fool-proof as much as possible to avoid
errors and accidents.
The robot should also be capable of a module
removal, which is approximated by the reverse
process of module placement.

4. Robot hardware
As illustrated conceptually in Fig. 3, the robot
consists functionally of three major components
each with an associated movement system. These
are: a module manipulator with a module chucking head, a pair of screw drivers and a pair ofmonitor CCD cameras. The robot also has somesensors. For example, a pair of induction sensors
embedded in the chucking head measure Z
position (radial distance) of the cooling pipe
surface which is nearly the same as the Z positionof the bracket surface. Thus, the robot directly
recognizes how far it should reach toward thebracket for each module mounting cycle. Also themanipulator is equipped with stress sensors so thatit can come to an immediate halt when it
encounters an accidental contact against obstacles.

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The robot moves on a linear stage (X1) set inparallel to the cylinder axis. The manipulator has amodule chucking head, two rotation joints (y1 andy2) and a set of linear stages (Y2 and Z2). Thosestages and joints can be operated simultaneously
in an accordant way.
The robot is required to have other movable
joints and stages for precise adjustments toCCD cameras
Chucking head
X3
Y3

Z3

θ2

X2
θ1

Manipulator Z2147

compensate variations of the module dimensions,errors of the bracket positions, setting errors of thecylinder and so on. All the movable joints andstages are shown in Fig. 3. Their features andfunctions are summarized in Table 1.
Position reproducibility of the manipulator andother moving mechanisms is better than 25 mm,
and the accuracy of all position adjustments is also
better than 25 mm.
Fig. 4 is a picture of the robot together with thesimulation barrel stand shown in the left and thecontrol rack in the right. Shown in Fig. 5 is a closeup of the head of the robot manipulator. Here, adummy barrel module held by the robot is about
to be brought to the bracket on the simulation
barrel stand.

Screw drivers

Y2

5. Control system and software
X1

Z1
Fig. 3. Concept of the module placement robot.

The control system consists of a graphic touch
panel, a programmable logic controller and amotion controller. A pair of stage controllers withTable 1
Movable joints and stages of the robot
Movabledirections

Roles and functions

Range (mm)Powered with

Comments

X1

1600

Stepping motor

100

Ditto

Manipulator, cameras and screw
drivers move all at once
Ditto

10DittoY2

Movement along the cylinder
axis
Movement to the fall-backposition
Manipulator position
adjustment
Movement of manipulator

100

Ditto

Z2
y1

Movement of manipulator
Head rotation in Y 2Z plane

DittoDitto

y2

Head rotation in X 2Y plane

Ditto

Rotation for the stereo angle

X3

Movement of cameras

100
051 tilt fromvertical, clickstop at 901
720 mR with
72 mR ﬁneadjustment
100

Air cylinder

Y3

Overall height adjustment

10Stepping motor

Z3

Movement of screw drivers

200

Ditto

Between regular and recessed
positions
Adjustment of cameras and screw
drivers
Movement to recessed positions,and progression for screw fastening

Z1
X2

Adjustment of manipulator wrt
camerasMovement of module to support
bracket
Ditto
Movement of module to support
bracket, module pick-up

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S. Terada et al. / Nuclear Instruments and Methods in Physics Research A 541 (2005) 144–149

Fig. 4. Picture of the robot together with a simulation barrel
stand shown in the left and the control rack in the right.

Fig. 5. Close-up of the robot head; the robot holding a module
is approaching toward the bracket on the simulation barrel
stand.

manual controller pendants for ﬁne adjustment isalso attached to the system. The conceptual layoutof the system is shown in Fig. 6.
The graphic touch panel, which is equipped witha CPU, works as the central commander in thesystem. It collects all the information, such asstage positions, various sensor outputs, camera
views, screw driver status and so on. Based on thisinformation, it examines the status of the robot
and makes a judgment whether to proceed to thenext step. It provides for a human operator, aguide and an instruction about what to do for the
next step. Each step is initiated by an operator
through use of the graphic touch panel.
The programmable logic controller has sets ofpreprogrammed strings of action steps. Eachstring corresponds to a speciﬁc action sequencesuch as the movement from A to B in Fig 2.
Following an order initiated from the graphic
touch panel, the programmable logic controllerchooses an appropriate string for the required
action step. Then the programmable logic controller issues corresponding commands to themotion controller.
The actual movement of each basic action isdeﬁned by preprogramming the motion controller.
The motion controller sends a set of corresponding
signals to the movable components i.e. the stages,
joints and so on to make them move coherently toperform a required action step.
A set of operation software was developed using
a conventional PC. Then, the corresponding
programs were downloaded to the graphic touch
panel, programmable logic controller and motion
controller, respectively.
Overall operation and control is done by thegraphic touch panel.
The system was programmed to provide various
operation modes including: the motion checkmode, the module placement mode, the module
removal mode and the error recovery mode.
All movable stages and joints can be individually operated and checked in the motion checkmode. The module placement and module removal
modes are the sequences of the module placement
and removal processes, respectively. When amalfunctions or miss-operation occurs, the program automatically goes into the error recovery
mode. In this mode, the task is immediatelyceased. Then it examines the situation by collecting
all the information and instructs the operator how
to bring the robot back to a safe position. For each
operation mode there are guides and cautions on
the graphic panel for the operator.

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Placement Jig

Y3
CCD camera
Chucking head X3

Y3

θ2

Z3

Z3

X2

θ2

θ1X2

Screw driver
Z2

Z2

Screw driver controller
Graphic touch panel

θ1
Y2
|‚
X1
X1
Stage controller

Y2

Z1

Z1

Motor drivers
Programmable logic controller

Manual pendants

Motion controller

Fig. 6. Conceptual drawing of the operating system.

6. Conclusions
We developed the semi-automatic work robot
dedicated for the task of the SCT barrel module
placement. The robot was carefully developed andtuned using the barrel simulation stand. It wasveriﬁed that the robot handled the barrel module
reliably and securely with an accuracy of about
25 mm. In practice, it took about 10 min to mount
one module cautiously with deliberate precautions.
Several operation modes have been provided todeal with various situations. The error recovery
process was particularly emphasized to make theoperation as safe as possible.
Further tunings and improvements may beneeded, however, to cope with the actual barrel

assembly. Interlocks and safety measures should
be carefully examined by means of the real barrel
cylinders.

References[1] ATLAS Technical Proposal for a General-Purpose Experiment at the Large Hadron Collider at CERN, CERN/
LHCC/94-43, December 1994.
[2] ATLAS Inner Detector Technical Design Report, CERN/
LHCC/97-16, 17.
[3] T. Kondo, et al., Nucl. Instr. and Meth. A 485 (2002) 27.
[4] H. Kobayashi, Master Thesis, University of Tsukuba,March 2000.
H. Sengoku, Master Thesis, University of Tsukuba, March2004.