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VSAs @ IRL

Three types of Variable Stiffness Actuators @ IRL
  • Research Background
    • Simultaneous control of position and stiffness is required for the dexterous manipulation.
    • Compliant motion is advantageous to contact motion as well as dynamic motion.
  • Research Objectives
    • Development of an actuator unit capable of providing simultaneous control of position and stiffness
    • Development of a small and light-weight actuator unit for robotic applications
  • Research Outcomes

  • Related Documents
    • Jae-Bok Song and Byeong-Sang Kim, Three Types of Dual Actuator Units for Variable Impedance Actuation, Variable Impedance Actuation Workshop (VIA 2010) .
    • Jae-Bok Song, Variable Stiffness Actuation based on Dual Actuators Connected in Series and Parallel, Robotics Science and Systems Workshop (RSS2008).



Hybrid type  Variable Stiffness Actuators (HVSA)

  • Research Period
    • 2009. 06. ~ Current.

  • Research Outcomes
    • The adjustable moment arm mechanism is adopted for the stiffness variation.
    • The modified planetary gear train is used for the compact design of actuator unit.
    • Constant stiffness irrespective of passive deflection can be achieved.

  • Control of Position and Stiffness

  • Hitting Blocks
    • Fast retraction motion is required to avoid collapse of the stack of the blocks.
    • Using variable stiffness control is advantageous to dynamic motion.

  • Playing Darts
    • From the conversion of potential energy to kinetic energy, the joint velocity can be increased faster than the motor velocity.

  • Related Papers/Patents
    • Paper 1. Byeong-Sang Kim and Jae-Bok Song, Design and Control of a Variable Stiffness Actuator based on Adjustable Moment Arm, IEEE Transactions on Robotics (Accepted as short paper)
    • Paper 2. Byeong-Sang Kim and Jae-Bok Song, Hybrid Dual Actuator Unit: A Design of a Variable Stiffness Actuator based on an Adjustable Moment Arm Mechanism, Proc. of IEEE Int. Conf. on Robotics and Automation (ICRA 2010), pp. 1655-1660, 2010. (ICRA2010 Best Automation Paper Finalist
    • Patent 1. Active Actuator Module (10-2010-0030725, Domestic)



Parallel type  Variable Stiffness Actuators (PVSA)

  • Research Period
    • 2008. 03. ~ 2010. 02.

  • Research Outcomes
    • Two actuators are antagonistically connected to control the position and stiffness simultaneously.
    • The linear characteristic of spring is converted to nonlinear via the cam-follower mechanism.
    • The dual cam-follower mechanism is used for the compact design of an actuator unit.
    • Collision safety is mechanically guaranteed when the external torque is larger than the user-specified force.

  • Position and stiffness control
    • (a) → (b): Increase of joints stiffness while maintaining position
    • (a) → (c): Position while maintaining joint stiffness
    • (a) → (d): Simultaneous control of position and stiffness


  • Collision Safety 
    • The features of collision safety can be obtained by designing the cam profile.
    • AAM: Antagonistic Actuation Mode for simultaneous control of position and stiffness.
    • CSM: Collision Safe Mode for collision safety.


  • Demonstration
    • Hammering a Nail
      • High impact force can be obtained from the conversion of potential energy to kinetic energy. 
      • Damage of gear reducer and motor can be avoided since the passive element absorbs the impact force.
    • Cutting a Zucchini
      • High impact force can be obtained from the conversion of potential energy to kinetic energy.
      • Damage of gear reducer and motor can be avoided since the passive element absorbs the impact force.
  • Related Papers/Patents
    • Paper 1. Ki-Hoon Nam, Byeong-Sang Kim and Jae-Bok, Song, Compliant Actuation of Parallel-type Dual Actuator Unit based on Antagonistic Actuation, Journal of Mechanical Science and Technology (JMST), Vol. 24, No. 11, pp. 2315-2321, 2010. 
    • Patent 1. Active Actuator Module and Active Actuator System Having the Same (10-2009-0092786, Domestic)

Serial type  Variable Stiffness Actuators (SVSA)
  • Research Outcomes
    • Two actuators are connected in series via the planetary gear train.
    • The positioning actuator (PA) has high gear ratio for high poisoning accuracy.
    • The stiffness actuator (SA) has low gear ratio for soft manipulation.
    • The joint stiffness can be adjusted by controlling the current of the SA.
    • Joint torque can be estimated by measuring the encoder information provided by two encoders.

  • Internal motion of SVSA

  • Environment Estimation
    • Stiffness estimation: Stiffness of the environment can be estimated by measuring the contact force and the displacement.
    • Surface estimation: The shape of the environment can be estimated while maintaining low contact force.

  • Wall Following
    • Contact force can be modulated by using force estimation feature of SVSA.
    • With force estimation: The manipulator can follow an arbitrary shaped wall while maintaining a small variation of contact force.
    • Without force estimation: The contact force varies as the manipulator follows the wall.
  • Related Papers/Patents
    • Paper 1. Byeong-Sang Kim, Jung-Jun Park, Jae-Bok Song, Serial-type Dual Actuator Unit with Planetary Gear Train: Basic Design and Applications, IEEE/ASME Transactions on Mechatronics (TMECH), Vol. 15, No. 1, pp. 108-116, 2010. 
    • Paper 2. Byeong-Sang Kim, Jae-Bok Song, Environment Estimation using Serial-type Dual Actuator Unit Capable of Force Estimation, Proc. of Int. Conf. on Ubiquitous Robots and Ambient Intelligence (URAI 2008), pp. 395-399, 2008.11. 
    • Paper 3. Byeong-Sang Kim, Jung-Jun Park, Jae-Bok Song, Double Actuator Unit with Planetary  Gear Train for a Safe Manipulator, Proc. of IEEE Int. Conf. on Robotics and Automation (ICRA 2007), pp. 1146-1151, 2007. 
    • Paper 4. Byeong-Sang Kim, Jung-Jun Park, Jae-Bok Song, Improved Manipulation Efficiency using a Serial-type Dual Actuator Unit, Proc. of Int. Conf. on Control, Automation and Systems (ICCAS 2007), pp. 30-35, 2007.10. 
    • Patent 1: Double Actuator Unit, Double Actuator Apparatus with the same and the method for controlling the Double Actuator Apparatus (10-0835908)

- Last updated: 2012. 5. 9