PurposeThe purpose of this paper is to review the current application areas of shape memory alloy (SMA) actuators in intelligent robotic systems and devices.Design/methodology/approachThis paper analyses how actuation and sensing functions of the SMA actuator have been exploited and incorporated in micro and macro robotic devices, developed for medical and non‐medical applications. The speed of response of SMA actuator mostly depends upon its shape and size, addition and removal of heat and the bias force applied. All these factors have impact on the overall size of the robotic device and the degree of freedom (dof) obtained and hence, a comprehensive survey is made highlighting these aspects. Also described are the mechatronic aspects like the software and hardware used in an industrial environment for the control of such nonlinear actuator and the type of sensory feedback devices incorporated for obtaining better control, positioning accuracy and fast response.FindingsSMA actuators find wide applications in various facets of robotic equipments. Selecting a suitable shape, fast heating and cooling method and better intelligent control technique with or without feedback devices could optimize its performance.Research limitations/implicationsThe frequency of SMA actuation purely depends on the rate of heat energy added to and removed from the actuator, which in turn depends upon interrelated nonlinear parameters.Practical implicationsFor increasing the dof of robots, number of actuators also have to be increased that leads to complex control problems.Originality/valueExplains the suitability of SMA as actuators in smart robotic systems, possibility of miniaturisation. It also highlights the difficulties faced by the SMA research community.

The Exechon 5-Axis Parallel Kinematic Machine (PKM) is a successful design created in Sweden and adopted by many producers of machine tools around the world. A new version of the manipulator is being developed as a component of a mobile self-reconfigurable fixture system within an inter-European project. The basic Exechon architecture consists of a 3-degree-of-freedom (dof) parallel mechanism (PM) connected in series with a two- or three-dof spherical wrist. The PM has two UPR (4-dof) legs, constrained to move in a common rotating plane, and an SPR (5-dof) leg. The paper presents the kinematic analysis of both the PM and the hybrid parallel-serial architecture. We describe the complex three-dimensional motion pattern of the PM platform, derive the kinematic equations and provide explicit solutions for the inverse kinematics.

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Virtual reality tracking devices are rapidly becoming the go-to system for cost-effective motion tracking solutions across different communities such as robotics, biomechanics, sports, rehabilitation, motion simulators, etc. This article focuses on the spatial tracking performance of HTC Vive's lighthouse tracking system (VLTS) devices (tracker, controller, and head mount display). A comprehensive literature survey on the performance analysis of VLTS on the various aspects is presented along with its shortcomings in terms of spatial tracking evaluation. The two key limitations have been identified: in static cases, there is a lack of standard procedures and criteria, and in dynamic cases, the entire study of spatial tracking. We address the first by assessing VLTS using the optical tracking system standard specified by ASTM International, and the latter by revising the standards to determine the upper-velocity limit for reliable tracking. The findings are substantiated with the trajectories of human wrist motion. Each evaluation's results are systematically analyzed with statistical hypothesis tests and criteria fulfillment. Comau NS16, an industrial serial robot, was used as the ground truth motion generator due to its repeatability and 6 degrees of workspace freedom. One of the major reasons for not having more generalized spatial tracking studies is that the tracking performance heavily depends on the configurations of the setup, work volume, environment, etc. Thus, the guidelines for configuring VLTS and the approach adapted from ASTM standards for evaluating VLTS for custom applications using our reported findings for both static and dynamic cases are included in the appendix.

This paper reviews recent developments in nonlinear control technologies for shape memory alloy (SMA) actuators in robotics and their related applications. SMA possesses large hysteresis, low bandwidth, slow response, and non-linear behavior, which make them difficult to control. The fast response of the SMA actuator mostly depends upon, (1) type of controller, (2) rate of addition and removal of heat, and (3) shape or form of the actuator. Though linear controllers are more desirable than nonlinear ones, the review of literature shows that the results obtained using nonlinear controllers were far better than the former one.\ud Therefore, more emphasis is made on the nonlinear control technologies taking into account the intelligent controllers. Various forms of SMA actuator along with different heating and cooling methods are presented in this review, followed by the nonlinear control methods and the control problems encountered by the researchers