Introducing Pleated Pneumatic Artificial Muscles for the Actuation of Legged Robots : a One-dimensional Set-up (original) (raw)
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Pleated Pneumatic Artificial Muscles for Robotic Applications
2003
This work describes the implementation of Pleated Pneumatic Artificial Muscles (PPAM) into innovative robotic applications. These actuators have a very high power to weight ratio and an inherent adaptable compliance. Two applications for which these characteristics give interesting surplus values are described. Nowadays legged robots are gaining more and more interest. But most of the robots use electrical drives making these machines heavy and power consuming. An actuator, such as the PPAM lowers the robot weight and the adaptable compliance of the muscles can be exploited to reduce energy consumption. In order to substantiate the benefits of the PPAM, a two-dimensional walking biped "LUCY" has been built. For robot manipulators, which interact with humans to support them with some heavy-duty tasks, the compliance of the PPAM can assure a "soft-touch". Moreover it is possible to estimate exerted force and torque values by measuring the applied gauge pressures in the different artificial muscles. This provides an important tool to generate manipulator force and torque feedback without expensive and complex sensor devices.
Design of a Biped Actuated by Pleated Pneumatic Artificial Muscles
This paper presents the design of a biped actuated by Pleated Pneumatic Artificial Muscles. These actuators have a very high power to weight ratio and an inherent adaptable compliance. The mechanical design of the bipedal robot is modular, making parts easy to change and replace. The frame of the robot is made out of a high-grade aluminium alloy. The weight of the machine, all included, is about 30 kg and its height 150 cm. The applied control has two levels: a high level controller for the complete system and a low level controller for each joint, locally implementing the high level decisions. The high level controller runs on a PC and each low level controller is implemented on a 16-bit microcontroller and operates a set of fast switching pneumatic on-off valves that set the muscle pressures in order to follow required trajectories. All microcontrollers are linked to the PC through a dual ported ram unit that acts as a buffer and data transfer agent on a 16 bit parallel asynchronous bus. The paper discusses in detail the different concepts of our design. Special attention is given to the flexibility of the mechanical construction and the elaborate control hardware because through these an adaptable and broad experimental platform is ensured.
Second generation pleated pneumatic artificial muscle and its robotic applications
Advanced Robotics, 2006
This paper reports on the second generation of the Pleated Pneumatic Artificial Muscle (PPAM) which has been developed to extend the life span of its first prototype. This type of artificial was developed to overcome dry friction and material deformation which is present in the widely used McKibben type of artificial muscle. The essence of the PPAM is its pleated membrane structure which enables the muscle to work at low pressures and at large contractions. There is a growing interest in this kind of actuation for robotics applications due to its high power to weight ratio and the adaptable compliance, especially for legged locomotion and robot applications in direct contact with a human. This paper describes the design of the second generation PPAM, for which specifically the membrane layout has been changed. In function of this new layout the mathematical model, developed for the first prototype, has been reformulated. This paper gives an elaborate discussion on this mathematical model which represents the force generation and enclosed muscle volume. Static load tests on some real muscles, which have been carried out in order to validate the mathematical model, are then discussed. Furthermore are given two robotic applications which currently use these pneumatic artificial muscles. One is the biped Lucy and the another one is a manipulator application which works in direct contact with an operator.
Pleated pneumatic artificial muscles: actuators for automation and robotics
2001 IEEE/ASME International Conference on Advanced Intelligent Mechatronics. Proceedings (Cat. No.01TH8556), 2001
This contribution reports on a type of pneumatic artificial muscles (PAMs) that was recently developed at the Vrije Universiteit Brussel, department of Mechanical Engineering. Its distinguishing feature is its pleated design. Due to this, it has a very high contraction force and an equally high travel. The weight of these pleated PAMs is very low: a muscle of only 60 gr can pull up to 3500 N and contract by an amount of 42%. Furthermore, dry friction and associated hysteresis, typical of many other designs, is avoided by the folding-unfolding action. This significantly simplifies position control using these actuators. Although the force-displacement characteristics of our actuators are non-linear, they can be effectively controlled using basic linear PI techniques. Another advantage of these actuators is their inherent and controllable compliance, making them ideally suited for walking/running machines or whenever delicate tasks, e.g. handling fragile objects, have to be performed. In view of all characteristics pleated PAMs are very well suited for automation and robotic applications.
Electric-Pneumatic Actuator: A New Muscle for Locomotion
Actuators
A better understanding of how actuator design supports locomotor function may help develop novel and more functional powered assistive devices or robotic legged systems. Legged robots comprise passive parts (e.g., segments, joints and connections) which are moved in a coordinated manner by actuators. In this study, we propose a novel concept of a hybrid electric-pneumatic actuator (EPA) as an enhanced variable impedance actuator (VIA). EPA is consisted of a pneumatic artificial muscle (PAM) and an electric motor (EM). In contrast to other VIAs, the pneumatic artificial muscle (PAM) within the EPA provides not only adaptable compliance, but also an additional powerful actuator with muscle-like properties, which can be arranged in different combinations (e.g., in series or parallel) to the EM. The novel hybrid actuator shares the advantages of both integrated actuator types combining precise control of EM with compliant energy storage of PAM, which are required for efficient and adjustable locomotion. Experimental and simulation results based on the new dynamic model of PAM support the hypothesis that combination of the two actuators can improve efficiency (energy and peak power) and performance, while does not increase control complexity and weight, considerably. Finally, the experiments on EPA adapted bipedal robot (knee joint of the BioBiped3 robot) show improved efficiency of the actuator at different frequencies.
LUCY, a Bipedal Walking Robot with Pneumatic Artiflcial Muscles
2000
This paper describes the biped Lucy and it's control architecture that will be used. Lucy is actuated by Pleated Pneumatic Artiflcial Muscles, which have a very high power to weight ratio and an inherent adaptable com- pliance. These characteristics will be used to make Lucy walk in a dynamically stable manner while exploiting the adaptable passive behavior of these muscles.
Improving Power to Weight Ratio of Pneumatically Powered Legged Robots
Advances in Climbing and Walking Robots - Proceedings of 10th International Conference (CLAWAR 2007), 2007
Legged Robots require actuators with a high power to weight ratio. Although pneumatic actuators do not perform well in this regard, they have other attractive characteristics which are useful in Legged Robots. This paper describes a mechanical solution for significantly improving the payload capacity of a robot powered with pneumatic cylinders, Robug IV, and reports on the theoretical design and experimental outcomes.
Experimental Results on the First Movements of the Pneumatic Biped “Lucy”
This paper presents the biped Lucy and the first experimental results of this robot. Lucy is actuated by Pleated Pneumatic Artificial Muscles, which have a very high power to weight ratio and an inherent adaptable compliance. These characteristics will be used to make Lucy walk in a dynamic stable way while exploiting the adaptable passive behaviour of these muscles. The paper will describe briefly the concept of the pleated pneumatic artificial muscle and the creation of the revolute joint used for the biped. The design and implementation of the pressure control unit will be discussed followed by an overview of the complete robot. During the assembly and debugging phase of the robot a quasi-static global control has been implemented while using adapted PID techniques for the local feedback joint control. These initial control techniques resulted in the first movements of Lucy, which will be shown and discussed.
The power to weight ratio of the actuators is an important design factor for running robots. In this regard pleated pneumatic artificial muscles are excellent actuators. Another advantage is that they can actuate a joint directly, avoiding the additional weight of a gearbox. Obviously the weight of the pressure control valves has to be taken into consideration as well. For this application, standard pressure regulating valves are rather heavy and slow. An intelligently controlled array of fast switching on-off valves was tested as an alternative. Ways to decrease the opening and closing times of these valves are discussed in this paper. Simulations and experimental results will be compared. The design of a modular rotational joint with an antagonistic setup of two pleated pneumatic artificial muscles will be presented.
Torque and compliance control of the pneumatic artificial muscles in the biped "Lucy
Proceedings 2006 IEEE International Conference on Robotics and Automation, 2006. ICRA 2006., 2006
In the biped Lucy Pleated Pneumatic Artificial Muscles are used instead of electrical motors to power the joints, because in an antagonistic setup both the torque and the compliance are controllable. The muscles have also a high power to weight ratio and they can reduce impact effects. Interesting characteristics that can be exploited for legged robots. In this paper a control strategy is discussed where a torque control unit tracks a predefined trajectory and a compliance controller is used to reduce control efforts and energy consumption by fitting the compliance of the actuator to the natural compliance of the desired trajectory. The first part of this paper focusses on the torque control unit for the biped. The proposed control architecture consists of the joint trajectory generator and the joint trajectory tracking controller. The trajectory generator calculates trajectories represented by polynomials based on objective locomotion parameters, which are average forward speed, step length, step height and intermediate foot lift. The joint trajectory tracking controller is divided in three parts: a computed torque module, a delta-p unit and a bang-bang pressure controller. Results of the incorporation of this control architecture in the real biped Lucy are given. Several essential graphs showing tracking performance and pressure regulation are given and the effectiveness of the control algorithm is discussed. A second part of the paper focusses on the compliance controller which is experimentally tested on a one DOF pendulum. A mathematical formulation to exploit the natural dynamics with respect to different walking patterns for this purpose is explained. The experimental results show the effectiveness and importance of the adaptation strategy.