a magnetic lead screw with variable stiffness mechanism...4 variable stiffness actuator* (vsa) •...

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A Magnetic Lead Screw with Variable Stiffness Mechanism LDIA2019 Akira Heya* Yoshihiro Nakata Hiroshi Ishiguro Katsuhiro Hirata Osaka University, Japan

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  • 1

    A Magnetic Lead Screwwith Variable Stiffness Mechanism

    LDIA2019

    Akira Heya* Yoshihiro Nakata

    Hiroshi Ishiguro Katsuhiro Hirata

    Osaka University, Japan

  • 2

    Introduction

    Magnetic structure

    Variable stiffness mechanism

    Characteristics analysis

    Conclusion

    Contents

  • 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

  • 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

  • 5

    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

  • 6

    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.

  • 7

    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.

  • 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.

  • 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

  • 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

  • 11Purpose

    Proposal of a novel MLSwhich can actively change the stiffness

    Force Force

    Magneticphase

    Magneticphase

    Conventional Proposed

    Flexible interaction & High-power operation

  • 12Contents

    Introduction

    Magnetic structure

    Variable stiffness mechanism

    Characteristics analysis

    Conclusion

  • 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

  • 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

  • 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

    Stiffness can be adjusted by changing the angle of divided nut A

    Screw

  • 16Contents

    Introduction

    Magnetic structure

    Variable stiffness mechanism

    Characteristics analysis

    Conclusion

  • 17Characteristics analysis

    Evaluated model

    z

    y38 mm 38 mm

    3 mm

    1.5 mm

    Number of elements: 2,330,085Number of nodes: 403,724

  • 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

  • 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

  • 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

  • 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

  • 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

  • 23

    Thank you for your attention!

  • 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

  • 25Previous research

    Upper limb mechanism Flexible motion by compliance control