a magnetic lead screw with variable stiffness mechanism...4 variable stiffness actuator* (vsa) •...
TRANSCRIPT
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1
A Magnetic Lead Screwwith Variable Stiffness Mechanism
LDIA2019
Akira Heya* Yoshihiro Nakata
Hiroshi Ishiguro Katsuhiro Hirata
Osaka University, Japan
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2
Introduction
Magnetic structure
Variable stiffness mechanism
Characteristics analysis
Conclusion
Contents
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3Introduction
Nextage(Kawata Robots)
HAL(CYBERDYNE)
ASIMO(HONDA)
Collaborative robots and exoskeleton robots
• Safety for human-robot interaction
• Need force-controllable actuators
Lightweight, compact, and backdrivable
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4
Variable stiffness actuator* (VSA)
• Stiffness changed by moving pivot pointConsists of ball screw, two motors, and springs
*A. Jafari et al., “AwAS-II: A New Actuator with Adjustable Stiffness based on the Novel Principle of Adaptive Pivot point and Variable Lever ratio”, ICRA 2011
Introduction
Problemvibration, noise, decrease in drive efficiency
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Transmits forces without mechanical contact
Advantage• Reduction of particle emission• Low noise• High efficiency drive• Force limit when overloaded
Magnetic Lead Screw (MLS)
Nut
NS N
S NS N
S
NS N
S NS N
S
Screw
A. Heya et al., “Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator”, IEEE Trans. Magn., vol.54, no. 11, 8207805, 2018.
Rotary motor and encoder NutScrew
Linear encoder
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Transmits forces without mechanical contact
Advantage• Reduction of particle emission• Low noise• High efficiency drive• Force limit when overloaded
Magnetic Lead Screw (MLS)
Nut
NS N
S NS N
S
NS N
S NS N
S
Screw
A. Heya et al., “Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator”, IEEE Trans. Magn., vol.54, no. 11, 8207805, 2018.
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Transmits forces without mechanical contact
Advantage• Reduction of particle emission• Low noise• High efficiency drive• Force limit when overloaded
Magnetic Lead Screw (MLS)
Nut
NS N
S NS N
S
NS N
S NS N
S
Screw
A. Heya et al., “Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator”, IEEE Trans. Magn., vol.54, no. 11, 8207805, 2018.
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8
Transmits forces without mechanical contact
Advantage• Reduction of particle emission• Low noise• High efficiency drive• Force limit when overloaded
Magnetic Lead Screw (MLS)
Nut
NS N
S NS N
S
NS N
S NS N
S
Screw
A. Heya et al., “Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator”, IEEE Trans. Magn., vol.54, no. 11, 8207805, 2018.
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9Previous research
(a) Wang et al., Analysis of a Magnetic Screw for High Force Density Linear Electromagnetic Actuators, IEEE Trans. Magn., 2011(b) Heya et al., Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator, IEEE Trans. Magn.,2018(c) Heya et al., Analysis of a Consequent-Pole Magnetic Lead Screw, Proc. CEFC2018, 2018
Back yoke
Inner yokeSpiral PM Screw
Arc-shape PM
Magnetic teeth
Nut
Screw
Nut
Screw
Magnetic teeth
Arc-shape PM
Magnetic teeth
Screw
Force
Displacement
Operating principle
① ②
(a) Spiral surface permanent MLS (b) Interior permanent MLS
(c) Consequent-pole MLS (CPMLS)
Backyoke
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10Previous research
Stiffness of magnetic spring is depend on its hardware design
Back yoke
Inner yokeSpiral PM
Backyoke
ScrewArc-shape PM
Nut
Screw
Nut
Screw
(c) Consequent-pole MLS (CPMLS)
Magnetic teeth
Arc-shape PM
Magnetic teeth
Screw
Force
Displacement
Operating principle
① ②
(a) Spiral surface permanent MLS (b) Interior permanent MLS
Magnetic teeth
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11Purpose
Proposal of a novel MLSwhich can actively change the stiffness
Force Force
Magneticphase
Magneticphase
Conventional Proposed
Flexible interaction & High-power operation
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12Contents
Introduction
Magnetic structure
Variable stiffness mechanism
Characteristics analysis
Conclusion
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13Conceptual diagram of VSA
System configurationConventional Proposed
Rotarymotor A
Rotarymotor B
Rotarymotor A
Rotarymotor B
θs
θn
Nut A Nut B
Force
Mechanical springNut part
Relative rotational angle between nuts:Changed by motor rotation
Screw
Displacement of spring:Changed by motor rotation
Rotary motor A : For drivingRotary motor B : For adjusting stiffness
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14Proposed structure
Magnetic flux pathOverview
Magnetization Magnetic flux
Divided nut A
Divided nut B
Output plate
Screw(double-thread)
Rotation θn
Linear motion p
PM of divided nut A
Back yoke
x
y
• Design based on the CPMLS
z
x
y
Screw thread
Consequent-pole
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15Variable stiffness mechanism
…
…
…
…
θn: 0deg.θs: 0deg.
…
…
…
…
θn: 30deg.θs: -15deg.
θn: 60deg.θs: -30deg.
θn: 90deg.θs: -45deg.
…
…
…
…
Divided nut A Divided nut B①
②
③
④
Stiffness can be adjusted by changing the angle of divided nut A
Screw
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16Contents
Introduction
Magnetic structure
Variable stiffness mechanism
Characteristics analysis
Conclusion
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17Characteristics analysis
Evaluated model
z
y38 mm 38 mm
3 mm
1.5 mm
Number of elements: 2,330,085Number of nodes: 403,724
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18Characteristics analysis
Analysis conditions• Rotation angle : -90 to 90 deg.• Displacement: -3 to 3 mm
Rotation θn
Displacement p
Divided nut A
Divided nut B
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19Analysis results
Thrust/Torque characteristics:Changed by rotation of the nut A• Max. thrust/torque: 67.3 N / 63.8 mNm
Torque [mNm]
-3 -2 -1 0 1 2 3-90
-60
-30
0
30
60
90
Ro
tati
on
an
gle
θn
[deg.]
Displacement p [mm]
60
40
20
0
-20
-40
-60
Thrust [N]
60
40
20
0
-20
-40
-60
-3 -2 -1 0 1 2 3
Displacement p [mm]
-90
-60
-30
0
30
60
90
Rota
tion a
ngle
θn
[deg.]
Thrust characteristics Torque characteristics
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20Analysis results
Stiffness characteristics:Changed by rotation of the nut AVariable stiffness characteristics can be achieved
Thrust characteristics
Torque [mNm]
-3 -2 -1 0 1 2 3-90
-60
-30
0
30
60
90
Ro
tati
on
an
gle
θn
[deg.]
Displacement p [mm]
60
40
20
0
-20
-40
-60
Thrust [N]
60
40
20
0
-20
-40
-60
-3 -2 -1 0 1 2 3
Displacement p [mm]
-90
-60
-30
0
30
60
90
Rota
tion a
ngle
θn
[deg.]
-80
-60
-40
-20
0
20
40
60
80
-3 -2 -1 0 1 2 3
Th
rust
[N
]
Displacement [mm]
0 deg.30 deg.60 deg.90 deg.
Stiffness
Stiffness characteristics
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21Analysis results
Stiffness characteristics:Changed by rotation of the nut AVariable stiffness characteristics can be achieved
-80
-60
-40
-20
0
20
40
60
80
-3 -2 -1 0 1 2 3
Th
rust
[N
]
Displacement [mm]
0 deg.30 deg.60 deg.90 deg.
Stiffness
Stiffness characteristics Stiffness characteristics
0
10
20
30
40
50
60
70
80
90
90 60 30 0
Sti
ffn
ess
[N
/mm
]
Rotation angle θn [deg.]
Increase
Stiffness value
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22Conclusion
Proposal of a variable stiffness MLS
• Variable stiffness mechanism using a rotation of divided nut
• Designed the magnetic structure based on CPMLS
• Characteristics were clarified by 3-D FEM
Variable stiffness were achieved by the proposed mechanism
Future work
Design of a prototype and validity verification
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Thank you for your attention!
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24Previous research
(a) Spiral SPMLS
(a) Wang et al. : “Analysis of a Magnetic Screw for High Force Density Linear Electromagnetic Actuators, 2011(b) Ling et al. : “Design of a New Magnetic Screw With Discretized PMs”, 2016(c) Heya et al. : “Force Estimation Method for a Magnetic Lead-Screw-Driven Linear Actuator”, 2018(d) Heya et al. : “Analysis of a Consequent-Pole Magnetic Lead Screw”, 2018
Back yoke
Inner yoke Spiral PM
(c) Interior PMLS (IPMLS)
Backyoke
ScrewArc-shape PM
Magnetic teeth
(b) Discrete spiral SPMLS
Inner yoke
Back yoke
Discrete spiral PM
(d) Consequent-pole MLS (CPMLS)
Magnetic teeth
Arc-shape PM
Magnetic teeth
Screw
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25Previous research
Upper limb mechanism Flexible motion by compliance control