Investigation of particle jamming for compliant robotic arm and soft robotics

Abstract

In recent years, research in compliant and soft robotics has made great progress and become one of the fastest developing fields in the robotic research community. Because of their superior and inherent compliant property, soft robots exhibit great advantages in application scenarios requiring safe interactions, good adaptability, and bionics. However, many challenges remain to be solved, e.g. reliable and repeatable stiffness modulation, precise control, energy efficient actuation, etc. Among these challenges, the lack of suitable and effective stiffness modulation methods is a huge obstacle for their practical applications. In view of the challenges, the aim of this thesis is to investigate different jamming techniques, particle jamming, in particular, to modulate the stiffness of compliant robotic arms and soft robots. For compliance, a novel jamming method is proposed and demonstrated in compliant robots. For variable stiffness, passive jamming is found effective, especially when deformation rage is large. Apart from stiffness modulation, active particle jamming is also found as an effective soft actuation method. First, ball joints have been cascaded for compliant robotic arms with stiffness control. In the proposed ball joint design, the clearance between the ball and the socket can be kept or closed resulting different stiffness. When required easy rotation, the clearance in the ball joint is kept large. When needed large stiffness at the joint, a force is exerted to close the clearance. The stiffness depends on the magnitude of the force applied. Secondly, passive particle jamming is proposed for variable stiffness applications in soft robotics. Packed into a sheath and integrated with a traditional soft pneumatic bending actuator, particles in the sheath will jam as the actuator bends. The larger the bending angle, the stiffer the actuator becomes. This property is important for grasping heavy objects. Thirdly, apart from stiffness variation, jamming is also effective as an actuation method. A jamming state can be broken due to changes of boundary conditions when forces among particles reach a new equilibrium. By adjusting the amount of particles injected into a soft actuator, the range of bending and stiffness can both be controlled. Unlike pneumatic/hydraulic soft actuators that require both sealing and tether, the proposed particle transmission method allows soft actuators to be designed without the need of tether and sophisticated sealing. Lastly, an actively controlled and variable stiffness palm based on jamming is proposed and embedded into a robotic hand design. Controlled by vacuum pressure, the palm is adaptive to object shape with variable stiffness. The one degree of freedom mechanism for the palm provides an active control to ensure good contacts between the palm and the object in grasping applications. In summary, jamming has been investigated as a stiffness variation method of compliant robotic arms and soft robots. This thesis has shown a number of novel designs and applications based on jamming. Both theoretic and experimental studies have shown jamming’s effectiveness in stiffness variation. It is believed that studies in this thesis will provide useful information for other researchers to develop more novel jamming based stiffness variation applications.