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A newly developed rotary-linear motion platform with a giant magnetostrictive actuator
CIRP Annals - Manufacturing Technology 62 (2013) 371–374
Contents lists available at SciVerse ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er . com /ci r p/ def a ult . asp
A newly developed rotary-linear motion platform with a giant magnetostrictive actuator Hayato Yoshioka *, Hidenori Shinno (1), Hiroshi Sawano Precision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Positioning Spindle Giant magnetostrictive actuator
Demands for machining and measuring three-dimensional geometries have recently increased in a variety of industries. In order to meet such demands, it is necessary to develop a compact versatile high performance spindle system. This paper presents a newly developed rotary motion platform combined with a linear motion mechanism driven by a giant magnetostrictive actuator. The developed platform can be characterized by a compact structure, a noncontact structure, and high accuracy. Performance evaluation results confirm that the developed platform provides precise linear motion during rotating. ß 2013 CIRP.
1. Introduction Demands for fabricating and measuring of high accurate threedimensional (3D) patterns and geometries have recently increased in various industrial fields, because the functional surfaces which consist of periodic or nonperiodic fine 3D geometries create new remarkable characteristics such as water repellency and wear resistance [1,2]. For generating precise and fine geometric patterns on the workpiece surface, a piezoelectric actuator-driven tool is widely used [3]. In particular, many studies on fast tool servo (FTS) technique for turning process have been performed [4,5]. In order to achieve high performance machining and measuring the functional surfaces, it is useful to develop a new motion platform which can simultaneously achieve multi-degree-offreedom motion, such as an X, Y, and C axis motion table system [6,7] and a rotary-axial motion spindle system [8]. These multidegree-of-freedom systems make possible high efficient form generation and inspection of the structured surfaces. This paper presents a newly developed rotary-linear motion platform. The developed rotary-linear motion platform employs a giant magnetostrictive material (GMM) as an actuator for driving linear motion and provides precise linear motion during rotating in a noncontact condition. Performance evaluation results confirm that the developed platform is capable of achieving accurate rotary-linear motion. 2. Concept of the proposed rotary-linear motion platform 2.1. Properties of giant magnetostrictive material A conventional method for realizing simultaneously rotary and linear motion is to employ a stacked structure with a linear motion stage and a spindle unit such as a tool axis in a machine tool. In this structure, however, the moving mass is too large to achieve precise
* Corresponding author. 0007-8506/$ – see front matter ß 2013 CIRP. http://dx.doi.org/10.1016/j.cirp.2013.03.137
and quick motion for machining or measuring complex 3D geometries. Inversely, an FTS with a piezoelectric actuator for driving a cutting tool is available for turning process and provides high performance tool positioning which is short stroke but quick and precise. It is, however, difficult to apply the FTS technique to milling process with rotational tools because piezoelectric actuators require electric wiring to apply electric field for driving. The GMM is one of the useful functional materials for actuator. The GMM has a unique characteristic which strain of material is generated by applied magnetic field to the element. In general, the GMMs have the following features in comparison with piezoelectric materials; (1) (2) (3) (4) (5)
large displacement, high Curie temperature, noncontact driving without electrodes, large generated stress (force), and Ease of fabricating various shape design.
Due to the above mentioned properties, the GMMs have been used for the tool positioning in an ultraprecision lathe [9] or the vibration polisher for ultraprecision finishing [10]. 2.2. Design concept of the rotary-linear motion platform Fig. 1 shows a design concept of a rotary-linear motion platform. The proposed platform employs a giant magnetostrictive actuator (GMA) for driving a moving part in the axial direction. In this concept, the GMA is installed on a rotating shaft, and coil units are fixed on a nonrotating part such as spindle housing. The expansion of the GMA can be controlled by magnetic flux generated in a noncontact condition without electric wiring to the actuator. Fig. 1(b) shows a driving principle of the platform. The magnetic flux generated by coil current passes though stationary and rotating parts made of magnetic material which are colored with blue. All magnetic flux is concentrated to the GMA located at the center of rotating part, and the expansion of the GMA
372
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
Rotating spindle Giant magnetostrictive actuator
Coil Diaphragm for preloading
(a) Component of the platform
Nonmagnetic material Magnetic material Magnetic flux
Fig. 2. Structural configuration of the developed platform.
Linear motion (b) Linear motion driven by GMA expansion Fig. 1. Concept of the proposed rotary-linear motion platform.
pushes an end face. In consequence, the GMA in the rotational spindle provides precise linear motion during rotating. A similar rotary-linear motion mechanism driven by a magnetic actuator [8] has been proposed for actuating a rotating shaft in the axial direction. The mechanism proposed can be also applied to conventional machining spindles because it is enough to install an additional driving unit with GMA on the end face of the rotary spindle. Furthermore, this linear actuation during rotation provides quick response and accurate positioning, so that it can be applied to FTS for milling process and ultrasonic vibration milling. 3. Prototype development of the platform Fig. 3. Appearance of the developed platform.
3.1. Structural configuration of the prototype platform Fig. 2 shows the structural configuration of the prototype platform based on the above mentioned concept. The prototype consists of three principal units: a driving unit, a coil unit, and a measuring unit. The driving unit with a GMA was coaxially arranged with the rotating axis. The GMM used in the driving unit was Terfenol-D (Tb0.27Dy0.73Fe1.9) of a cylindrical form with a diameter of 20 mm and a length of 50 mm. The GMA was preloaded by a diaphragm element. The coil unit had a solenoid coil of 1260 turns inside the steel housing and the coil was arranged coaxially with the driving unit. In addition the coil unit was fixed on a base in this prototype, and the coil was connected with an electric amplifier. The measuring unit employed an optical fiber displacement sensor in order to minimize noise due to the coil current for driving. The sensor measured linear motion of the end face of driving unit from underneath. In actual applications, however, it is difficult to adapt such a configuration due to the interference with tool. Therefore, for example, a displacement sensor can be installed into the coil housing and axial displacement of the flange face is measured. The appearance of the prototype platform is shown in Fig. 3. The driving unit was set to a rotational spindle of a milling machine. The coil unit and the measuring unit were fixed on a work table of the machine. Fig. 4 shows the developed driving unit and the coil unit. In the prototype, rotation of the driving unit was
Fig. 4. The driving and the coil units.
provided by the spindle of the milling machine, and the output of the displacement sensor was recorded with a data logger. 3.2. Basic characteristic of the platform Fig. 5 shows the magnetic flux density distribution measured on the inner side in the coil unit before assembling the driving unit. A gaussmeter was used for measuring the magnetic flux density. The magnetic flux density generated by the coil was almost constant at 100 mT along the circumferential direction. Therefore, magnetic flux applied to the driving unit is independent from rotational angle and the eddy current loss between the coil and the driving units is negligibly small. After assembling the driving unit, the measurement of GMA expansion was performed. In this evaluation, the displacement of
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
the unit was measured when the sinusoidal current reference with a frequency of 1 Hz and an amplitude of 1 A was applied to the amplifier with a function generator. Fig. 6 shows a relationship between the coil current and the displacement of the platform without displacement feedback. As shown in the figures, the platform can be driven by applying current to the coil. However, a large hysteresis was observed in the displacement characteristic at any rotational speed. In addition, the driven part of the platform expanded to same direction in both the cases that the coil current was positive or negative. Although the measured characteristics at rotational speeds of 770 and 4000 rpm were influenced by run-out, this characteristic was independent of the rotational speed. Therefore, it is necessary and indispensable to employ a feedback control system for accurate positioning in order to reduce this hysteresis in expansion behavior. Fig. 7 shows the frequency response between the input to a current amplifier and the displacement of GMA at a rotational speed of 1750 rpm. The coil current and a frequency range were set to 2 A and 1 Hz to 10 kHz. Gain goes down beyond 10 Hz and changes 20 dB/decade, and this approximates the behavior of a first order system. As shown in this figure, the driving unit does not have any remarkable resonance or peak frequency, hence it is easy to control the displacement.
373
0
Gain [dB]
-20 -40 -60 -80 1
10
100 Frequency [Hz]
1000
10000
Fig. 7. Frequency response between the input to amplifier and the displacement of GMA.
Controller Kp
zref +
KI
-
Current amp.
Coil
GMA
z
s Displacement sensor
z
: Position
zref : Reference
K p : Proportional gain K I : Integral gain
Magneticfluxdensity [mT]
120 Fig. 8. Block diagram of the developed platform.
110
3.3. Positioning controller of the developed platform
100
Fig. 8 shows the block diagram of the developed controller for precision positioning. The full closed loop control system with an optical fiber displacement sensor feedback was implemented to compensate the positioning error caused by the hysteresis. A DSP unit was used as a PI compensator with a control frequency of 10 kHz. It is necessary to precisely control magnetic flux density at a GMA for achieving high performance positioning. Hence a current amplifier was used for controlling the coil current which generates magnetic flux. The proportional and integral gains in the controller were experimentally tuned after determination by Ziegler–Nichols ultimate sensitivity method.
90 80
π/2
0
π Angle [rad]
3π/2
2π
Fig. 5. Magnetic flux density along the circumferential direction.
4000rpm
20
4. Performance evaluation of the developed platform
15
Performances of the platform were evaluated through typical positioning experiments. Fig. 9 shows the results of step positioning of 20 mm at rotational speeds of 0, 770, and 4000 rpm. The response at 0 rpm shows a clear step response without overshoot. Although the responses at 770 and 4000 rpm include periodical vibration caused by run-out of the measured face, they indicate almost same responses as that at 0 rpm. Fig. 10 shows the determined rise time and the delay time at each rotational speed. In this study, the rise time was determined as the time from 10% to 90% of the response to the step input, and the delay time was defined as the time to achieve 50% of the step input,
10 5 0 -1 -0.5 0 0.5
1
-1 -0.5 0 0.5
1
-1 -0.5 0 0.5
1
Current [A] Fig. 6. Relationship between coil current and displacement.
25
Displacement [µm]
Displacement [µm]
770rpm
0rpm
25
20 15 10 5
0 rpm
0 -5 -0.4
-0.2
0
0.2
0.4
Time [s]
0.6
0.8
770 rpm 1.0 -0.4 -0.2
0
0.2
0.4
0.6
0.8
4000 rpm 1.0 -0.4 -0.2
Time [s] Fig. 9. Step response of the developed platform at each rotational speed.
0
0.2
0.4
Time [s]
0.6
0.8
1.0
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
374
50
Rise t ime Delay t ime
Time [ms]
40 30 20 10 0 0
1000
2000
3000
4000
Rotational speed [ rpm]
Displacement [µm]
Fig. 10. Rise time and delay time of response at each rotational speed.
20 15 10 5
respectively. These parameters were almost constant in a range of 4000 rpm. Therefore, these positioning results confirm that the platform can realize linear motion during rotation without hardwiring in a wide range of rotational speeds. Fig. 11 shows the responses to continuous square position reference at rotational speeds of 0 rpm and 4000 rpm. No remarkable difference between the responses can be observed. The second and the subsequent responses, however, got slightly slower than the first one in the responses at both 0 and 4000 rpm. This deterioration of response was caused by the hysteresis of the GMA as shown in Fig. 6. In addition, the positioning resolution of the developed platform was evaluated. Five forward and backward stepwise references were applied to the system. Fig. 12 shows the responses at 0 and 4000 rpm. As shown in this figure, the positioning resolution of 10 nm can be observed in a nonrotating condition. During rotating at 4000 rpm, a positioning resolution of 1 mm was achieved. Table 1 shows the basic specifications of the platform. These evaluation results confirmed that the rotary-linear motion platform developed has a capability for achieving precision linear motion in rotary mechanisms.
0 rpm 0
5. Conclusions
Displacement [µm]
-5 This paper presented a newly developed rotary-linear motion platform for precision machines. From the evaluation results of the prototype, the following conclusions could be drawn:
20 15 10 5
4000 rpm
0 -5
0
2
4
6
8
10
12
14
(1) A new rotary-linear motion platform was developed with a GMA which can be driven without electric wiring. (2) The platform can drive during rotation, and the positioning characteristics are almost same under any rotational speed. (3) The platform achieves the linear positioning resolution of 10 nm at 0 rpm and of 1 mm at 4000 rpm.
Time [s] The platform has the hysteresis of GMA, hence further studies on reduction in hysteresis effects will be required in next step.
Fig. 11. Response to square reference.
0.06
Measured Reference
Displacement[µm]
0.05
Acknowledgements
0.04
This research project was financially supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (S) No. 24226004 and (B) No. 24360052.
0.03 0.02 0.01
0rpm, 10nm References
0 -0.01
Displacement [µm]
7 6
Measured Reference
5 4 3 2 1
4000rpm, 1µm
0 -1 -2
0
1
2
3
4
5
Time [s] Fig. 12. Positioning resolution of the system. Table 1 Basic specifications of the developed platform. GMA dimensions Maximum axial stroke Maximum rotational speed Maximum force Axial positioning resolution
Ø 20 mm 50 mm 25 mm with current of 1.5 A >4000 rpm >3900 N at 0 mm 10 nm (0 rpm), 1 mm (4000 rpm)
[1] Bruzzone AAG, Costa HL, Lonardo PM, Lucca DA (2008) Advances in Engineered Surfaces for Functional Performance. CIRP Annals – Manufacturing Technology 57(1):750–769. [2] Brinksmeier E, Riemer O, Glabe R, Lunemann B, Kopylow Cv, Dankwart C, Meier A (2010) Submicron Functional Surfaces Generated by Diamond Machining. CIRP Annals – Manufacturing Technology 59(1):535–538. [3] Altintas Y, Woronko A (2002) A Piezo Tool Actuator for Precision Turning of Hardened Shafts. CIRP Annals – Manufacturing Technology 51(1):303–306. [4] Patterson SR, Magrab EB (1985) Design and Testing of a Fast Tool Servo for Diamond Turning. Precision Engineering 7(3):123–128. [5] Lu X-D, Trumper DL (2005) Ultrafast Tool Servos for Diamond Turning. CIRP Annals – Manufacturing Technology 54(1):383–388. [6] Shinno H, Hashizume H, Yoshioka H, Komatsu K, Shinshi T, Sato K (2004) X–Y–u Nano-Positioning Table System for a Mother Machine. CIRP Annals – Manufacturing Technology 53(1):337–340. [7] Shinno H, Yoshioka H, Taniguchi K (2007) A Newly Developed Linear MotorDriven Aerostatic X–Y Planar Motion Table System for Nano-Machining. CIRP Annals – Manufacturing Technology 56(1):369–372. [8] Lu X-D, Paone MP, Usman I, Moyls B, Smeds K, Rotherhofer G, Slocum AH (2009) Rotary-axial Spindles for Ultra-precision Machining. CIRP Annals – Manufacturing Technology 58(1):323–326. [9] Eda H, Ohmura E (1992) Ultraprecise Machine Tool Equipped with a Giant Magnetostriction Actuator – Development of New Materials, TbxDy1 x(FeyMn1 y)n, and Their Application. Annals of the CIRP 41(1): 421–424. [10] Guo J, Morita S, Hara M, Yamagata Y, Higuchi T (2012) Ultra-precision Finishing of Micro-aspheric Mold Using a Magnetostrictive Vibrating Polisher. CIRP Annals – Manufacturing Technology 61(1):371–374.
Contents lists available at SciVerse ScienceDirect
CIRP Annals - Manufacturing Technology jou rnal homep age : ht t p: // ees .e lse vi er . com /ci r p/ def a ult . asp
A newly developed rotary-linear motion platform with a giant magnetostrictive actuator Hayato Yoshioka *, Hidenori Shinno (1), Hiroshi Sawano Precision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Positioning Spindle Giant magnetostrictive actuator
Demands for machining and measuring three-dimensional geometries have recently increased in a variety of industries. In order to meet such demands, it is necessary to develop a compact versatile high performance spindle system. This paper presents a newly developed rotary motion platform combined with a linear motion mechanism driven by a giant magnetostrictive actuator. The developed platform can be characterized by a compact structure, a noncontact structure, and high accuracy. Performance evaluation results confirm that the developed platform provides precise linear motion during rotating. ß 2013 CIRP.
1. Introduction Demands for fabricating and measuring of high accurate threedimensional (3D) patterns and geometries have recently increased in various industrial fields, because the functional surfaces which consist of periodic or nonperiodic fine 3D geometries create new remarkable characteristics such as water repellency and wear resistance [1,2]. For generating precise and fine geometric patterns on the workpiece surface, a piezoelectric actuator-driven tool is widely used [3]. In particular, many studies on fast tool servo (FTS) technique for turning process have been performed [4,5]. In order to achieve high performance machining and measuring the functional surfaces, it is useful to develop a new motion platform which can simultaneously achieve multi-degree-offreedom motion, such as an X, Y, and C axis motion table system [6,7] and a rotary-axial motion spindle system [8]. These multidegree-of-freedom systems make possible high efficient form generation and inspection of the structured surfaces. This paper presents a newly developed rotary-linear motion platform. The developed rotary-linear motion platform employs a giant magnetostrictive material (GMM) as an actuator for driving linear motion and provides precise linear motion during rotating in a noncontact condition. Performance evaluation results confirm that the developed platform is capable of achieving accurate rotary-linear motion. 2. Concept of the proposed rotary-linear motion platform 2.1. Properties of giant magnetostrictive material A conventional method for realizing simultaneously rotary and linear motion is to employ a stacked structure with a linear motion stage and a spindle unit such as a tool axis in a machine tool. In this structure, however, the moving mass is too large to achieve precise
* Corresponding author. 0007-8506/$ – see front matter ß 2013 CIRP. http://dx.doi.org/10.1016/j.cirp.2013.03.137
and quick motion for machining or measuring complex 3D geometries. Inversely, an FTS with a piezoelectric actuator for driving a cutting tool is available for turning process and provides high performance tool positioning which is short stroke but quick and precise. It is, however, difficult to apply the FTS technique to milling process with rotational tools because piezoelectric actuators require electric wiring to apply electric field for driving. The GMM is one of the useful functional materials for actuator. The GMM has a unique characteristic which strain of material is generated by applied magnetic field to the element. In general, the GMMs have the following features in comparison with piezoelectric materials; (1) (2) (3) (4) (5)
large displacement, high Curie temperature, noncontact driving without electrodes, large generated stress (force), and Ease of fabricating various shape design.
Due to the above mentioned properties, the GMMs have been used for the tool positioning in an ultraprecision lathe [9] or the vibration polisher for ultraprecision finishing [10]. 2.2. Design concept of the rotary-linear motion platform Fig. 1 shows a design concept of a rotary-linear motion platform. The proposed platform employs a giant magnetostrictive actuator (GMA) for driving a moving part in the axial direction. In this concept, the GMA is installed on a rotating shaft, and coil units are fixed on a nonrotating part such as spindle housing. The expansion of the GMA can be controlled by magnetic flux generated in a noncontact condition without electric wiring to the actuator. Fig. 1(b) shows a driving principle of the platform. The magnetic flux generated by coil current passes though stationary and rotating parts made of magnetic material which are colored with blue. All magnetic flux is concentrated to the GMA located at the center of rotating part, and the expansion of the GMA
372
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
Rotating spindle Giant magnetostrictive actuator
Coil Diaphragm for preloading
(a) Component of the platform
Nonmagnetic material Magnetic material Magnetic flux
Fig. 2. Structural configuration of the developed platform.
Linear motion (b) Linear motion driven by GMA expansion Fig. 1. Concept of the proposed rotary-linear motion platform.
pushes an end face. In consequence, the GMA in the rotational spindle provides precise linear motion during rotating. A similar rotary-linear motion mechanism driven by a magnetic actuator [8] has been proposed for actuating a rotating shaft in the axial direction. The mechanism proposed can be also applied to conventional machining spindles because it is enough to install an additional driving unit with GMA on the end face of the rotary spindle. Furthermore, this linear actuation during rotation provides quick response and accurate positioning, so that it can be applied to FTS for milling process and ultrasonic vibration milling. 3. Prototype development of the platform Fig. 3. Appearance of the developed platform.
3.1. Structural configuration of the prototype platform Fig. 2 shows the structural configuration of the prototype platform based on the above mentioned concept. The prototype consists of three principal units: a driving unit, a coil unit, and a measuring unit. The driving unit with a GMA was coaxially arranged with the rotating axis. The GMM used in the driving unit was Terfenol-D (Tb0.27Dy0.73Fe1.9) of a cylindrical form with a diameter of 20 mm and a length of 50 mm. The GMA was preloaded by a diaphragm element. The coil unit had a solenoid coil of 1260 turns inside the steel housing and the coil was arranged coaxially with the driving unit. In addition the coil unit was fixed on a base in this prototype, and the coil was connected with an electric amplifier. The measuring unit employed an optical fiber displacement sensor in order to minimize noise due to the coil current for driving. The sensor measured linear motion of the end face of driving unit from underneath. In actual applications, however, it is difficult to adapt such a configuration due to the interference with tool. Therefore, for example, a displacement sensor can be installed into the coil housing and axial displacement of the flange face is measured. The appearance of the prototype platform is shown in Fig. 3. The driving unit was set to a rotational spindle of a milling machine. The coil unit and the measuring unit were fixed on a work table of the machine. Fig. 4 shows the developed driving unit and the coil unit. In the prototype, rotation of the driving unit was
Fig. 4. The driving and the coil units.
provided by the spindle of the milling machine, and the output of the displacement sensor was recorded with a data logger. 3.2. Basic characteristic of the platform Fig. 5 shows the magnetic flux density distribution measured on the inner side in the coil unit before assembling the driving unit. A gaussmeter was used for measuring the magnetic flux density. The magnetic flux density generated by the coil was almost constant at 100 mT along the circumferential direction. Therefore, magnetic flux applied to the driving unit is independent from rotational angle and the eddy current loss between the coil and the driving units is negligibly small. After assembling the driving unit, the measurement of GMA expansion was performed. In this evaluation, the displacement of
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
the unit was measured when the sinusoidal current reference with a frequency of 1 Hz and an amplitude of 1 A was applied to the amplifier with a function generator. Fig. 6 shows a relationship between the coil current and the displacement of the platform without displacement feedback. As shown in the figures, the platform can be driven by applying current to the coil. However, a large hysteresis was observed in the displacement characteristic at any rotational speed. In addition, the driven part of the platform expanded to same direction in both the cases that the coil current was positive or negative. Although the measured characteristics at rotational speeds of 770 and 4000 rpm were influenced by run-out, this characteristic was independent of the rotational speed. Therefore, it is necessary and indispensable to employ a feedback control system for accurate positioning in order to reduce this hysteresis in expansion behavior. Fig. 7 shows the frequency response between the input to a current amplifier and the displacement of GMA at a rotational speed of 1750 rpm. The coil current and a frequency range were set to 2 A and 1 Hz to 10 kHz. Gain goes down beyond 10 Hz and changes 20 dB/decade, and this approximates the behavior of a first order system. As shown in this figure, the driving unit does not have any remarkable resonance or peak frequency, hence it is easy to control the displacement.
373
0
Gain [dB]
-20 -40 -60 -80 1
10
100 Frequency [Hz]
1000
10000
Fig. 7. Frequency response between the input to amplifier and the displacement of GMA.
Controller Kp
zref +
KI
-
Current amp.
Coil
GMA
z
s Displacement sensor
z
: Position
zref : Reference
K p : Proportional gain K I : Integral gain
Magneticfluxdensity [mT]
120 Fig. 8. Block diagram of the developed platform.
110
3.3. Positioning controller of the developed platform
100
Fig. 8 shows the block diagram of the developed controller for precision positioning. The full closed loop control system with an optical fiber displacement sensor feedback was implemented to compensate the positioning error caused by the hysteresis. A DSP unit was used as a PI compensator with a control frequency of 10 kHz. It is necessary to precisely control magnetic flux density at a GMA for achieving high performance positioning. Hence a current amplifier was used for controlling the coil current which generates magnetic flux. The proportional and integral gains in the controller were experimentally tuned after determination by Ziegler–Nichols ultimate sensitivity method.
90 80
π/2
0
π Angle [rad]
3π/2
2π
Fig. 5. Magnetic flux density along the circumferential direction.
4000rpm
20
4. Performance evaluation of the developed platform
15
Performances of the platform were evaluated through typical positioning experiments. Fig. 9 shows the results of step positioning of 20 mm at rotational speeds of 0, 770, and 4000 rpm. The response at 0 rpm shows a clear step response without overshoot. Although the responses at 770 and 4000 rpm include periodical vibration caused by run-out of the measured face, they indicate almost same responses as that at 0 rpm. Fig. 10 shows the determined rise time and the delay time at each rotational speed. In this study, the rise time was determined as the time from 10% to 90% of the response to the step input, and the delay time was defined as the time to achieve 50% of the step input,
10 5 0 -1 -0.5 0 0.5
1
-1 -0.5 0 0.5
1
-1 -0.5 0 0.5
1
Current [A] Fig. 6. Relationship between coil current and displacement.
25
Displacement [µm]
Displacement [µm]
770rpm
0rpm
25
20 15 10 5
0 rpm
0 -5 -0.4
-0.2
0
0.2
0.4
Time [s]
0.6
0.8
770 rpm 1.0 -0.4 -0.2
0
0.2
0.4
0.6
0.8
4000 rpm 1.0 -0.4 -0.2
Time [s] Fig. 9. Step response of the developed platform at each rotational speed.
0
0.2
0.4
Time [s]
0.6
0.8
1.0
H. Yoshioka et al. / CIRP Annals - Manufacturing Technology 62 (2013) 371–374
374
50
Rise t ime Delay t ime
Time [ms]
40 30 20 10 0 0
1000
2000
3000
4000
Rotational speed [ rpm]
Displacement [µm]
Fig. 10. Rise time and delay time of response at each rotational speed.
20 15 10 5
respectively. These parameters were almost constant in a range of 4000 rpm. Therefore, these positioning results confirm that the platform can realize linear motion during rotation without hardwiring in a wide range of rotational speeds. Fig. 11 shows the responses to continuous square position reference at rotational speeds of 0 rpm and 4000 rpm. No remarkable difference between the responses can be observed. The second and the subsequent responses, however, got slightly slower than the first one in the responses at both 0 and 4000 rpm. This deterioration of response was caused by the hysteresis of the GMA as shown in Fig. 6. In addition, the positioning resolution of the developed platform was evaluated. Five forward and backward stepwise references were applied to the system. Fig. 12 shows the responses at 0 and 4000 rpm. As shown in this figure, the positioning resolution of 10 nm can be observed in a nonrotating condition. During rotating at 4000 rpm, a positioning resolution of 1 mm was achieved. Table 1 shows the basic specifications of the platform. These evaluation results confirmed that the rotary-linear motion platform developed has a capability for achieving precision linear motion in rotary mechanisms.
0 rpm 0
5. Conclusions
Displacement [µm]
-5 This paper presented a newly developed rotary-linear motion platform for precision machines. From the evaluation results of the prototype, the following conclusions could be drawn:
20 15 10 5
4000 rpm
0 -5
0
2
4
6
8
10
12
14
(1) A new rotary-linear motion platform was developed with a GMA which can be driven without electric wiring. (2) The platform can drive during rotation, and the positioning characteristics are almost same under any rotational speed. (3) The platform achieves the linear positioning resolution of 10 nm at 0 rpm and of 1 mm at 4000 rpm.
Time [s] The platform has the hysteresis of GMA, hence further studies on reduction in hysteresis effects will be required in next step.
Fig. 11. Response to square reference.
0.06
Measured Reference
Displacement[µm]
0.05
Acknowledgements
0.04
This research project was financially supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (S) No. 24226004 and (B) No. 24360052.
0.03 0.02 0.01
0rpm, 10nm References
0 -0.01
Displacement [µm]
7 6
Measured Reference
5 4 3 2 1
4000rpm, 1µm
0 -1 -2
0
1
2
3
4
5
Time [s] Fig. 12. Positioning resolution of the system. Table 1 Basic specifications of the developed platform. GMA dimensions Maximum axial stroke Maximum rotational speed Maximum force Axial positioning resolution
Ø 20 mm 50 mm 25 mm with current of 1.5 A >4000 rpm >3900 N at 0 mm 10 nm (0 rpm), 1 mm (4000 rpm)
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