This article presents the design principle and fabrication of a variable stiffness soft robotic gripper for adaptive grasping and robust holding. The proposed robotic gripper is based on a finger design that combines a fiber-reinforced soft actuator and a particle pack. The soft actuator is responsible for the bending motion of the finger, and the particle pack acts as a stiffness-changeable interface between the finger and the object. In the natural state, the particle pack is soft and adaptive to part geometry. It can rapidly stiffen (through vacuum) to resist external load or to freeze the currently bent contour of the finger. Experimental studies have shown that more than a 10-fold stiffness enhancement is achievable. Therefore, the proposed gripper is capable of handling objects with different shapes, weights, and rigidities, which have been a great challenge for robotic grasping. For more effective grasping, a grasping strategy is designed for the proposed soft gripper with simultaneous consideration of grasping adaption and robustness.

Early studies on robot machining were reported in the 1990s. Even though there are continuous worldwide researches on robot machining ever since, the potential of robot applications in machining has yet to be realized. In this paper, the authors will first look into recent development of robot machining. Such development can be roughly categorized into researches on robot machining system development, robot machining path planning, vibration/chatter analysis including path tracking and compensation, dynamic, or stiffness modeling. These researches will obviously improve the accuracy and efficiency of robot machining and provide useful references for developing robot machining systems for tasks once thought to only be capable by CNC machines. In order to advance the technology of robot machining to the next level so that more practical and competitive systems could be developed, the authors suggest that future researches on robot machining should also focus on robot machining efficiency analysis, stiffness map-based path planning, robotic arm link optimization, planning, and scheduling for a line of machining robots.

Despite the increasing popularity of soft robotic research, the application of soft robots is hindered by their limited ability to change compliance and acquire force and position feedback. In this article, both the controllability of compliance and the acquisition of position feedback are achieved in soft robotic fingers in the novel design of a three-dimensional (3D)-printed multismart material substrate. The substrate is composed of shape memory polymer (SMP) and conductive elastomer thermoplastic polyurethane (TPU). The SMP material is utilized to modulate the finger stiffness through its elastic modulus change around glass transition temperature (T_g). The conductive TPU has two functions: one is to tune SMP temperature by producing Joule heat when electrical power is supplied and the other is to provide position feedback of the finger by utilizing the piezoresistive effect of the conductive TPU. Theoretical modeling of finger position feedback and stiffness modulation are conducted. The theoretical analysis has been experimentally validated by a prototype robotic finger built from the proposed concept.

Grasping is an important characteristic of robots in interacting with humans and the environment. Due to the inherent compliance of soft grippers, they can easily adapt to novel objects and operate safely in a human-centered environment. However, soft hands suffer from poor grasping robustness and operation durability, especially for heavy objects or objects with sharp spikes, mainly due to their fragile material and low structural stiffness of the soft actuators. Thus, the widespread use of soft hands in daily applications is still limited. Existing works have shown a promising direction to enhance grasping performance by solving the contradiction between inherent compliance/adaptability and loading capacity. It is known that the stiffness of the robotic phalange is highly related to the performance of robotic hands. In this article, we propose a novel variable stiffness particle phalange, called VSPP here. The proposed VSPP exhibits variable stiffness characteristics without the need for dedicated actuation by utilizing passive particle jamming resulted from forces in interacting with the environment. The VSPP can cooperate with any kind of actuators, soft or rigid, to function as a compliant and robust robotic hand. A prototype robotic hand based on VSPP could maintain reliable grasping even when pierced by sharp objects such as a needle, a cactus, and a durian. This durability is effective both in air and underwater, thus presents new possibilities for the soft robotic hand to work in a harsh environment. The inherent multidirectional compliance of the VSPP makes safety in human/robot interaction guaranteed. The design and modeling presented in this research will provide useful guidance in VSPP applications. A prototype gripper, VSPP-3, composed of three 2-segments VSPP fingers and pneumatic joints, has been built for demonstrations in reliable and robust grasping of daily objects. The sample grasping has shown that the proposed VSPP has great potential for a robust and durable soft robotic hand or gripper design.