Electrically-induced actuation for open-loop control to cancel self-excitation vibration

Makihara, Kanjuro,Ecker, Horst Techno-Press 2012 Smart Structures and Systems, An International Jou Vol.9 No.2

This paper focuses on the actuation system combined with a piezoelectric transducer and an electric circuit, which leads to a new insight; the electric actuation system is equivalent to mechanical variable-stiffness actuation systems. By controlling the switch in the circuit, the electric status of the piezoelectric transducer is changed, and consequently a variable-stiffness mechanism is achieved on the electric actuator. This proposed actuator features a shift in the equilibrium point of force, while conventional electrically-induced variable-stiffness actuators feature the variation of the stiffness value. We intensively focus on the equilibrium shift in the actuation system, which has been neglected. The stiffness of the variable-stiffness actuator is periodically modulated by controlling the switch, to suppress the vibration of the system in an open-loop way. It is proved that this electric actuator is equivalent to its mechanical counterpart, and that the electrical version has some practical advantages over the mechanical one. Furthermore, another kind of electrically-induced variable-stiffness actuator, using an energy-recycling mechanism is also discussed from the viewpoint of open-loop vibration control. Extensive numerical simulations provide comprehensive assessment on both electrically-induced variable-stiffness actuators employed for open-loop vibration control.

Electrically-induced actuation for open-loop control to cancel self-excitation vibration

Kanjuro Makihara,Horst Ecker 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.9 No.2

This paper focuses on the actuation system combined with a piezoelectric transducer and an electric circuit, which leads to a new insight; the electric actuation system is equivalent to mechanical variablestiffness actuation systems. By controlling the switch in the circuit, the electric status of the piezoelectric transducer is changed, and consequently a variable-stiffness mechanism is achieved on the electric actuator. This proposed actuator features a shift in the equilibrium point of force, while conventional electricallyinduced variable-stiffness actuators feature the variation of the stiffness value. We intensively focus on the equilibrium shift in the actuation system, which has been neglected. The stiffness of the variable-stiffness actuator is periodically modulated by controlling the switch, to suppress the vibration of the system in an open-loop way. It is proved that this electric actuator is equivalent to its mechanical counterpart, and that the electrical version has some practical advantages over the mechanical one. Furthermore, another kind of electrically-induced variable-stiffness actuator, using an energy-recycling mechanism is also discussed from the viewpoint of open-loop vibration control. Extensive numerical simulations provide comprehensive assessment on both electrically-induced variable-stiffness actuators employed for open-loop vibration control.

가변 모멘트 암 기반의 소형 가변 강성 액추에이터 모듈

유홍선(Hong-Seon Yu),송재복(Jae-Bok Song) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.10

최근에 들어 로봇과 환경 사이의 상호작용이 다양하게 발생하는 작업에서 가변 강성 액추에이터의 연구가 활발하다. 기존의 다양한 가변 강성 액추에이터가 개발되었지만 크기와 중량 때문에 응용분야를 찾기가 어렵다. 따라서 다양한 분야에 쉽게 이용되기 위해 소형의 가변 강성 액추에이터(miniVSA)를 개발하였다. miniVSA는 모멘트 암 기반의 강성제어 장치와 두 개의 모터로 구성된 구동 장치로 구성된다. 강성제어 장치는 두 캠의 상대 운동을 제어하여 위치와 강성을 동시에 제어할 수 있다. 이를 실험을 통하여 강성 변화를 검증하였다. In recent years, variable stiffness actuation has attracted much attention because interaction between a robot and the environment is increasingly required for various robot tasks. Several variable stiffness actuators (VSAs) have been developed; however, they find limited applications owing to their size and weight. For realizing their widespread use, we developed a compact and lightweight mini-VSA. The mini-VSA consists of a control module based on an adjustable moment arm mechanism and a drive module with two motors. By controlling the relative motion of cams in the control module, the position and stiffness can be simultaneously controlled. Experimental results are presented to show its ability to change stiffness.

Experimental Study on Different Principles of Variable Stiffness Actuators

백규열(Kyu Yeol Baek),김현규(HyunGyu Kim),서태원(TaeWon Seo) Korean Society for Precision Engineering 2015 한국정밀공학회지 Vol.32 No.12

Nowadays, there are many researches involving structural actuators, which have adjustable stiffness; they are also called variable stiffness actuators (VSA). The VSAs can adjust the characteristics of actuators for various functions and human-machine safety. This paper describes the design and analysis of two types of VSAs. To adjust stiffness, the actuators are controlled by a principle of lever ratio mechanism, by changing a pivot position or a spring position in the structure with springs. To make the principle workable, the designs are simplified by using a ball screw system with a motor. Each structure shows different static properties with variable rates of stiffness. We have also shown the experimental verification of the dynamic performance of the two types of VSAs. This research can be applied to various industrial fields, where humans work in conjunction with robots.

Modified sigmoid based model and experimental analysis of shape memory alloy spring as variable stiffness actuator

Bhagoji B. Sul,K. Dhanalakshmi 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.24 No.3

The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

Employing variable impedance (stiffness/damping) hybrid actuators on lower limb exoskeleton robots for stable and safe walking trajectory tracking

Ozgur Baser,Hasbi Kizilhan,Ergin Kilic 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

Compliant actuators are employed in exoskeleton robots instead of stiff actuators for safe human-robot interaction. In parallel with this idea, we previously constructed a biomimetic compliant exoskeleton robot (BioComEx). In this study, to provide more stable and safe trajectory tracking even under disturbances, magneto-rheological (MR) brakes were added to all joints of BioComEx as variable damping actuators and a PID+D controller was proposed. To evaluate the robot and controller, first, BioComEx was hung on a platform and the controller was applied without device user under external forces. This primary test results showed that the proposed design and controller can effectively minimize disturbance effects and consequently reduce trajectory tracking oscillations. In the rest of the study, the similar control experiments were repeated with a user who has unilateral lower limb movement disorders. In these experiments, the movements of the user's healthy leg were detected by force feedback impedance control algorithm and then were used as reference for the impaired leg with walking cycle delay in real time. The secondary test results showed that the variable impedance exoskeleton robot design with PID+D controller can ensure effective walking assistance for the impaired human legs.

MR(Magneto-Rheological) Gel Soft Actuator-based Knee-Exosuit

윤정환,백윤수 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.04

Analysis of system dynamic influences in robotic actuators with variable stiffness

Philipp Beckerle,Janis Wojtusch,Stephan Rinderknecht,Oskar von Stryk 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.13 No.4

In this paper the system dynamic influences in actuators with variable stiffness as contemporary used in robotics for safety and efficiency reasons are investigated. Therefore, different configurations of serial and parallel elasticities are modeled by dynamic equations and linearized transfer functions. The latter ones are used to identify the characteristic behavior of the different systems and to study the effect of the different elasticities. As such actuation concepts are often used to reach energy-efficient operation, a power consumption analysis of the configurations is performed. From the comparison of this with the system dynamics, strategies to select and control stiffness are derived. Those are based on matching the natural frequencies or antiresonance modes of the actuation system to the frequency of the trajectory. Results show that exclusive serial and parallel elasticity can minimize power consumption when tuning the system to the natural frequencies. Antiresonance modes are an additional possibility for stiffness control in the series elastic setup. Configurations combining both types of elasticities do not provide further advantages regarding power reduction but an input parallel elasticity might enable for more versatile stiffness selection. Yet, design and control effort increase in such solutions. Topologies incorporating output parallel elasticity showed not to be beneficial in the chosen example but might do so in specific applications.

Analysis of system dynamic influences in robotic actuators with variable stiffness

Beckerle, Philipp,Wojtusch, Janis,Rinderknecht, Stephan,von Stryk, Oskar Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.4

In this paper the system dynamic influences in actuators with variable stiffness as contemporary used in robotics for safety and efficiency reasons are investigated. Therefore, different configurations of serial and parallel elasticities are modeled by dynamic equations and linearized transfer functions. The latter ones are used to identify the characteristic behavior of the different systems and to study the effect of the different elasticities. As such actuation concepts are often used to reach energy-efficient operation, a power consumption analysis of the configurations is performed. From the comparison of this with the system dynamics, strategies to select and control stiffness are derived. Those are based on matching the natural frequencies or antiresonance modes of the actuation system to the frequency of the trajectory. Results show that exclusive serial and parallel elasticity can minimize power consumption when tuning the system to the natural frequencies. Antiresonance modes are an additional possibility for stiffness control in the series elastic setup. Configurations combining both types of elasticities do not provide further advantages regarding power reduction but an input parallel elasticity might enable for more versatile stiffness selection. Yet, design and control effort increase in such solutions. Topologies incorporating output parallel elasticity showed not to be beneficial in the chosen example but might do so in specific applications.

Compliant actuation of parallel-type variable stiffness actuator based on antagonistic actuation

Ki-Hoon Nam,김병상,송재복 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.11

For a service robot requiring physical human-robot interaction, stable contact motion and collision safety are very important. To accomplish these functions, we propose a novel design for a parallel-type variable stiffness actuator (PVSA). The stiffness and position of a joint can be controlled simultaneously using the PVSA based on an antagonistic actuation inspired by the musculoskeletal system. The PVSA consists of a dual-cam follower mechanism, which acts like a human muscle, and a drive module with two motors. Each cam placed inside the dual cam-follower mechanism has two types of cam profile to provide a wide range of stiffness variation and collision safety. The use of the PVSA enables position and stiffness control to occur simultaneously. Furthermore, joint stiffness instantly decreases when the PVSA is subject to a high torque exceeding a pre-determined value, thereby improving collision safety. Experiments showed that the PVSA provides effective levels of variable stiffness and collision safety.