Design of Motorized Moving Stage with Submicron Precision

Design of Motorized Moving Stage with Submicron Precision
Tatag Lindu Bhakti, Adhi Susanto, Paulus Insap Santosa, Diah Tri Widayati / International
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 6, November- December 2012, pp.674-678
Design of Motorized Moving Stage with Submicron Precision
Tatag Lindu Bhakti1, Adhi Susanto2,
Paulus Insap Santosa3, Diah Tri Widayati4
1, 2, 3
Department of Electrical Engineering and Information Technology,
Faculty of Engineering, Gadjah Mada University.
Grafika Street No. 2, Yogyakarta, 55281. INDONESIA
4
Faculty of Animal Sience, Gadjah Mada University
Fauna Street No. 3, Bulaksumur, Yogyakarta, 55281. INDONESIA
Abstract
A motorized moving stage with
submicron precision is needed to support cellular
manipulation e.g. in vitro fertilization in cattle
breeding industry. This study aims to build an
automatic moving stage prototype which has two
degrees of freedom using hybrid stepper motor
connected mechanically with rails of the
microscope moving stage. Microscope stage
movement is fully controlled using main software
which connected logically to ATMEGA 8 through
serial communication chip proxy FT232RL.
Movement testing using OptiLab® Advanced
image processing software show if motorized
moving stage has smallest horizontal step
resolution 0.198 ± 0.001 µm/step with hysteresis
5.99 ± 1.09 µm and smallest vertical step
resolution 0.197 ± 0.004 µm/step with hysteresis
2.36 ± 1.28 µm in 16 sub-division microstep driver
setting. Motorized moving stage has also linear
response with R = 0.999 at various testing signal
frequencies.
There are three types of stepper motors: permanent
magnet (PM), variable reluctance (VR) and hybrid
[1][2][3]. Fig. 1 shows internal structure of three
type’s stepper motors. As its name implies,
permanent magnet stepper motor has a permanent
magnet drum on rotor core. Variable reluctance
stepper motor utilizes stator magnetic induction to
move soft iron materials contained on its rotator,
whereas hybrid stepper motor combines working
principles of PM and VR stepper motors with
jagged-magnetic surface design profile to create
high-resolution rotary step through caliper (vernier)
principle.
Keywords - Hybrid Linear Actuators, Stepper
Motor, Motorized Stage, Microscope Moving Stage,
Microstep Driver.
Fig. 1 Motor Structures (a)VR, (b)PM and (c)Hybrid
[2][3]
1. INTRODUCTION
2.2. Microstep Control
Stepper motor can be controlled using four
methods; wave step control, full step control, half
step control and microstep control. In wave step
control method, rotor movement is fully controlled
using single solenoid excitation while in full step
control; rotor movement is controlled using a pair of
opposite solenoid excitation. In half step control,
two pairs of stator solenoid excitation result a
certain angle of attack according to its rotating
center and in microstep control method, stepper
motor is controlled similarly with half step, but with
advanced phase-current control on each active
solenoid to make more precision step movement.
Cellular
manipulation
in
assisted
reproduction requires supporting equipment to help
livestock industry researcher and practitioner
performs gamete cells micromanipulation with less
error. The presence of submicron precision
automatic moving stage in livestock breeding
industry which can be fully controlled automatically
using software is expected to reduce gamete fusion
failure probability in assisted fertilization.
2. THEORETICAL BASIS
2.1. Stepper Motors
Stepper motors are type of motors which
designed to be installed on open loop control
system. Stepper motors generate discrete rotational
movement which relevant to their loop resolution
and can be operated accurately as predictions when
worked below their holding torque limit.
674 | P a g e
Tatag Lindu Bhakti, Adhi Susanto, Paulus Insap Santosa, Diah Tri Widayati / International
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 6, November- December 2012, pp.674-678
2.3. Hybrid Linear Actuator (HLA)
HLA is a linear actuator consisting of
hybrid stepper motor with extended rotator shaft
paired with screw cap to convert rotational
movement into linear movement. Fig. 4 shows the
physical appearance of HLA external type.
Fig. 2 Current Control in Each Phase to Create
Microstep movement [4][5]
There are three type’s microstep control
techniques; square line path, circle line path and
random line path. In square line path control, final
torque magnitude which generated through
interaction of two pairs solenoids is always greater
than or equal to maximum torque generated from
single solenoid element. In circular line path control,
final torque magnitude is always equal to maximum
torque generated from single solenoid element.
While in random line path control, final torque
magnitude has arbitrary value depends on
interaction between each active solenoid. Fig. 3
shows illustration of each microstep control
techniques.
Fig. 4 HLA External Type [6]
Fig. 5 shows converting mechanism from
rotational movement into translational movement in
HLA threaded shaft. Assuming all of rotational
steps can be perfectly transformed into linear steps,
amount of the linear displacement can be calculated
using (3)
Fig. 5 Converting Mechanism of Rotary Movement
into Translation Movement in HLA
is amount of linear displacement came from
rotational movement,
is distance between
Fig.
3 Three Types of Microstep Control
Techniques. (a)Square Line path, (b) Circular
Line path and (c) Random Line path[5]
If
represents amount of electrical current
passing through first phase of solenoid series,
represents amount of electrical current passing
through second phase of solenoid series and
is
total resistive barriers at each phase, then power
dissipation of microstep control
can be
formulated as follows (1)
with angle of attack
(2)
corresponding screw “teeth” (see Fig. 5),
is
number of full turning steps are needed by system to
make one full rotation (360o) and
is number of
steps generated from stepper motor. Amount of
can be calculated using (4)
Equation (4) shows that
depends on
value which represents smallest full step resolution
which can be generated by stepper motor without
has a slip and without microstep driving emulation.
2.4. ATMEGA 8 Microcontroller
Microcontroller is electronic devices which
can be programmed to execute specific application
routine. Physically, microcontroller is an integrated
circuit consisting of main processor, Random
675 | P a g e
Tatag Lindu Bhakti, Adhi Susanto, Paulus Insap Santosa, Diah Tri Widayati / International
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 6, November- December 2012, pp.674-678
Access Memory (RAM), permanent memory
(ROM) and input/output pin which can be utilized to
make communication with external devices.
Graphical
User
Interface
Cartesian
Coordinate
Separator
Speed
Controller
X-Axis Distance
Converter
Fig. 6 ATMEGA 8 Microcontroller [7]
3. CONSTRUCTION OF MICROSTEP
DRIVING MECHANISM
SOFTWARE
The single axis model of microstep driver
consists of four main parts: displacement-to-pulse
accumulation converter to translate set point
displacement into its associative pulse amount, pulse
generator, microstep movement controller and
hybrid linear actuator which driven by hybrid
stepper motor to handle microstep’s movement on
each stage axis. Movement control mechanism is
designed without feedbacks assuming HLA is
loaded under its holding torque limit to avoid any
slips step. Fig. 7 shows microstep movement control
algorithm.
Displacement
Setpoint (One
Dimension)
HARDWARE
Displacement-to-Pulse
Accumulation Converter
Intermodular
Communication
Management
USB Communication
Program Routine
(D2XX.dll)
SOFTWARE
Y HLA
HARDWARE
Fig. 6 shows physical appearance of
ATMEGA 8 microcontroller. In accordance to [7],
ATMEGA 8 is an 8-bit microcontroller produced by
ATMEL Corp. and come with 8 Kbyte Flash
PEROM (Programmable and Erasable Read Only
Memory) used to store main code. ATMEGA 8
processor can work up to 16 MHz clock frequencies
and designed using RISC (Reduced Instruction-Set
of Computing) processor architecture named
ATMEL AVR®.
Y-Axis Distance
Converter
Y-Axis HLA
Controller
Switching Power
Supply 24V/2A
X HLA
USB
Microcontroller:
TTL-to-USB:
FTDI 232RL
ATMEGA 8
X-Axis HLA
Controller
Low Noise Power
Supply 5V/1A
Fig. 8 Block Diagram of Motorized Moving Stage
Control
Motorized moving stage consists of
software and hardware parts which can be
communicated each other through USB (Universal
Serial Bus) as shown in Fig. 8. Main software is
used to make set point input for control system, set
HLA’s motion speed and calculate associative
amount of pulse needed to make precision
movement using constants calibration which has
been recorded in software code. Hardware is used to
generate real pulse signal as ordered from software
and realize it into physical movement steps with
submicron precision. An anti-backlash mechanism
is attached on HLA to minimize translational
hysteresis emerging at movement conversion
process as shown in Fig. 9.
Pulse
Generator
Microstep Movement
Controller
Hybrid Linear
Actuator
Fig. 7 Control Algorithm of Single Axis Motorized
Moving Stage
Fig. 9 Anti-Backlash Principle
Anti-backlash mechanism using spring
elasticity properties to give initial force on a pair of
linear actuator nut to reduce spatial clearances area
which occurs in mechanical contact area between
threaded shaft’s surface and nut inner surface. This
anti-backlash mechanism has been built to increase
HLA’s precision movement.
676 | P a g e
Tatag Lindu Bhakti, Adhi Susanto, Paulus Insap Santosa, Diah Tri Widayati / International
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 6, November- December 2012, pp.674-678
4. RESULTS OF MOTORIZED MOVING
STAGE DESIGN
HLA is driven by two phases-hybrid
stepper motor with dimension code: NEMA
(National Electrical Manufacturers Association) 11
as shown in Fig. 10. Stepper motor has working
voltage 4.0V/0.95A per phase and has full turning
step resolution
1.8°±5%. Movement converter
attached on HLA’s shaft with theoretical value
3.175 µm per full step (1.8o).
Fig. 11 HLA Assembled in XZS-107BN Stage
Red circle in Fig. 12 shows a limit switch
providing emergency stop for XY movement. It
used to make emergency stop and set zero point
reference for each axis. Movement restriction
procedure is necessary to protect HLA from
overdriving which potentially damaging mechanical
structures.
Fig. 10 HLA Installation on Microscope Moving
Stage (X-Axis and Y-Axis)
Each step movement of HLA’s motor is
controlled using microstep driver which preprogrammed using denumerator constant value as
listed in Table I. Theoretically, microstep driver can
handle stepper motor current up to 1.5 A per phase
at maximum working frequencies (20 KHz). Fig. 11
shows HLA installation in XZS HLA-107BN
biological light-microscope.
Table I. Implications of Denumerator Constant
Setting upon Linear Resolution Movement
Fig. 12 HLA’s Limit Switch
To get near-integer value of step movement
but still provides sufficient torque, stepper motor
driver is programmed at 16 sub-division setting
value with maximum operating frequency 18,519
KHz (pulse period 54 µs). According to Table I, 16
sub-division setting value will produce 3,675
µm/sec with 0.198 μm/step resolution on each axis.
Its driver setting allows HLA to make 1 μm
(approx.) displacement using 5 pulses.
Denumerator
Constant
(Sub-Division)
Theoretical Value:
1
3.1750
2
1.5875
4
0.7938
8
0.3969
5. TESTING RESULT
16
0.1984
32
0.0992
64
0.0496
5.1. Linearity Testing
Linearity testing of motorized moving
stage prototype is performed by actuating
microscope’s stage independently in one axis
direction then stage position is measured using 10
µm objective micrometer which interpolated using
OptiLab® Advanced image processing software. Fig.
13 shows linear movement testing result.
(µm/ pulse)
677 | P a g e
Tatag Lindu Bhakti, Adhi Susanto, Paulus Insap Santosa, Diah Tri Widayati / International
Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 6, November- December 2012, pp.674-678
vertical step hysteresis 2.36 ± 1.28 μm/step (square
dots).
CONCLUSION
Testing results show motorized moving
stage prototype has horizontal step resolution 0.198
± 0.001 μm/step with hysteresis 5.99 ± 1.09 μm and
vertical step resolution 0.197 ± 0.004 μm/step with
hysteresis 2.36 ± 1.28 μm with maximum speed
3,675µm/sec in 16 sub-divisions microstep driver
setting. Motorized moving stage has linear response
with R = 0.999 at various testing signal frequencies.
Fig. 13 Linear Response of Motorized Moving
Stage Prototype
Fig. 13 show motorized moving stage has
average horizontal microstep repeatability 0.198 ±
0.001 μm/step (y1) and vertical microstep
repeatability 0.197 ± 0.004 μm/step (y2). Motorized
moving stage has also linear response with R =
0.999 at various testing signal frequencies.
ACKOWLEDGEMENTS
Authors would thank to all of Civitas
Academica Electrical Engineering Department and
Animal Science Department Gadjah Mada
University and PT. Miconos Transdata Nusantara
(www.miconos.co.id) which provided facility for
motorized moving stage testing and calibration.
REFERENCES
[1]
5.2. Hysteresis Testing
Hysteresis testing is performed by
actuating microscope’s stage backward and forward
20 times repeatedly to obtain hysteresis response of
motorized stage. Fig. 14 shows results of hysteresis
testing using 10 µm objective micrometer reference
which interpolated using OptiLab® Advanced image
processing software
[2]
[3]
[4]
[5]
Fig. 14 Hysteresis Response of Motorized Moving
Stage Prototype
Testing results in Fig. 14 shows motorized
moving stage has average horizontal step hysteresis
5.99 ± 1.09 μm/step (diamond dots) and average
[6]
[7]
T. Kenjo, Stepping Motor and Their
Microprocessor Controls, Monographs in
Electrical and Electronic Engineering,
(Oxford University Press New York, ISBN
0-19-859326-0, 1984).
F. Eriksson, Stepper Motor Basics,
Industrial Circuits Application Note, 1998.
P. Yedamale and S. Chattopadhyay,
Stepper Motor Microstepping with
PIC18C452, AN822 Article, Microchip
Technology Inc., 2002.
X. Ma, G. An, and B. Li, Design and
Implementation
of
an
Automated
Microscope Stage, International Forum on
Information Technology and Applications,
ISBN
978-0-7695-3600-2/09,
DOI
10.1109/ IFITA.2009.268, 2009, 603-605.
Tutorial Microstepping, Available [Online]
at
http://www.zaber.com/wiki/Tutorials/
Microstepping.htm, retrieved on 18 July
2012.
Datasheet: Hybrid Linear Actuator
11E2045A4-095-001, Available [Online] at
http://www.ms-motor.com/
Datasheet: AT MEGA 8/L (Rev.2486Z–
AVR–02/11), Available [Online] at
http://www.atmel.com/
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