Hikaru Ishihara

Verification of throwing operation by a manipulator with variable viscoelastic joints with straight-fiber-type artificial muscles and magnetorheological brakes

Abstract The performance of a robot can be enhanced by increasing its output. However, increasing the output of rigid actuators such as motors and hydraulic actuators will likely increase the weight of the robot. Conversely, organisms such as human beings achieve high output within a short time by accumulating and releasing the elastic energy stored in their muscles; thus, providing an instantaneous force. Moreover, the viscoelastic properties of muscle enable organisms to control their instantaneous force outputs and overall movements. Therefore, in this study, we developed a manipulator with two-degree-of-freedom (DOF) variable viscoelastic joints. The manipulator comprised straight-fiber-type artificial muscles and a magnetorheological (MR) brakes. The ability of a manipulator to generate controlled movement from an instantaneous force was tested in a throwing operation. This simple two-DOF variable viscoelastic manipulator with apparent viscosity control by the MR brakes achieved successful throwing motions. However, it was not possible to calculate the experimental parameters from the target operation in previous study. Therefore, we focused on particle swarm optimization (PSO) as a parameter search method. In this paper, we try to optimize parameters of the throwing movement by combining the spring model of a two-DOF variable viscoelastic manipulator with the PSO method.

Throwing operations by manipulator with a 2-DOF variable viscoelastic joint using pneumatic artificial muscles and a magnetorheological brake

The performance of a robot can be enhanced by increasing its output. However, increasing the output of rigid actuators such as motors and hydraulic actuators will likely increase the weight of the robot. Conversely, organisms such as human beings achieve high output within a short time by accumulating and releasing the elastic energy stored in their muscles (thus providing an instantaneous force). Moreover, the viscoelastic properties of muscle enable organisms to control their instantaneous force outputs and their overall movements. Therefore, in this study, we developed a manipulator with a 2-degree-of-freedom (DOF) variable viscoelastic joint. The manipulator comprises a straight-fiber-type artificial muscle and a magnetorheological (MR) brake. The ability of the manipulator to generate controlled movement from an instantaneous force was tested in a throwing operation. This simple 2-DOF variable viscoelastic manipulator with apparent viscosity control by the MR brakes achieved successful throwing motions.

Landing method for a one-legged robot with artificial muscles and an MR brake

Bipedal robots capable of various dynamic motions - such as walking, running, and jumping - have been developed in recent years. In particular, these dynamic motions require high power for short durations of time when the robot kicks off the ground. Furthermore, it is necessary to reduce the impact force that a robot is subjected to when landing during these motions. When humans perform similar motions, they generate an instantaneous high-power force using an elastic element and dampen the impact force using a viscous element in their muscles. Therefore, a robotic leg designed for jumping that relies on these elements has been developed. It uses a straight-fiber-type artificial muscle and a magnetorheological (MR) brake. A previously designed one-legged robot was able to jump 82.5 mm using a sliding rail and counter weights; however, it shook upon landing due to an elastic element in its artificial muscles. Here, therefore, an MR brake to dissipate energy is applied to the robotic leg in order to suppress vibration. Landing experiments performed with the newly designed one-legged robot confirm that the proposed method (i.e., using the MR brake) is able to suppress vibrations.

Throwing motion with instantaneous force using a variable viscoelastic joint manipulator

This article focuses on developing a pneumatic artificial muscle as a variable elastic device and a magnetorheological fluid brake as a variable viscosity device and a variable friction device. We executed a throwing motion using a 2-degree-of-freedom manipulator as a case study of the control of dynamic motion. To investigate the throwing motion, we proposed the spring model of the manipulator, which includes a variable viscoelastic joint. Next, the manipulator and the spring model were extended to 2 degrees of freedom. In addition, the spring model was verified by comparing the simulation and experimental results. The simulation results reproduced the experimental results. Furthermore, we maximized the velocity of the end effector during the throwing motion by searching for adequate drive timing of the second joint in the simulation. In the simulation, hand speed was improved by releasing the second joint on the basis of the angular acceleration of the first joint. Finally, the simulation results were reproduced experimentally under the same conditions.

Optimization of Throwing Motion by 2-DOF Variable Viscoelastic Joint Manipulator

This paper focuses on control of variable viscoelasticity joint manipulator. Each joint consists of pneumatic rubber artificial muscle and magnetorheological fluid. And the joint can generate instantaneous force by accumulating potential energy in artificial muscle. Using instantaneous force appropriately, robots can perform dynamic motion such as jumping and throwing like a human. These motions are expected to contribute to the efficient transport of objects and improve the robot’s mobility. And also, elasticity and viscosity of joints are needed to control appropriately to achieve target task. Therefore, we proposed a method to control variable viscoelasticity of joint. We set throwing motion as a target task. And elasticity and viscosity are decided by simulation. In addition, simulation result is optimized by Particle Swarm Optimization (PSO) algorithm. Finally, we conducted throwing experiment to reproduce the simulation result. As a result, simulation result showed that elasticity and viscosity changed to accelerate end effector. However, experimental result showed deviations from simulation result because of model error.

Vertical jumping motion simulation with consideration for landing using a monopedal robot with artificial muscles and magnetorheological brakes

Bipedal robots capable of various dynamic motions such as walking, running, and jumping have been developed in recent years. In particular, these dynamic motions require the use of high power in a short time when the robot kicks off the ground. Furthermore, it is necessary to decrease the impact force that a robot is subjected to when landing during these motions. Unfortunately, rigid actuators tend to become heavier as their output increases. Therefore, we focus on the method for obtaining a high output using elastic energy. However, the use of the elastic element only leads to robot vibration. Therefore, to control the dynamic motion, we adopted the viscosity element to the robot joint. In this study, we focused on a straight-fiber-type artificial muscle for the elastic element and a magnetorheological brake for the viscosity and friction elements, respectively. A previously designed monopedal robot was able to jump 82.5 mm using a sliding rail and counter weights; however, the robot shook upon landing because of the presence of the elastic element in its artificial muscles. In this paper, we first proposed a dynamic model of the previously developed monopedal robot. We then performed vertical jumping simulations of the robot to confirm the models utility.