A Novel Concept for Safe, Stiffness-Controllable Robot Links

The recent decade has seen an astounding increase of interest and advancement in a new field of robotics, aimed at creating structures specifically for the safe interaction with humans. Softness, flexibility and variable stiffness in robotics have been recognised as highly desirable characteristics for many applications. A number of solutions were proposed ranging from entirely soft robots (such as those composed mainly from soft materials such as silicone), via flexible continuum and snake-like robots, to rigid-link robots enhanced by joints that exhibit an elastic behaviour either implemented in hardware or achieved purely by means of intelligent control. Although these are very good solutions paving the path to safe human-robot interaction, we propose here a new approach which focuses on creating stiffness controllability for the linkages between the robot joints. This paper proposes a replacement for the traditionally rigid robot link – the new link is equipped with an additional capability of stiffness controllability. With this added feature, a robot can accurately carry out manipulation tasks (high stiffness), but can virtually instantaneously reduce its stiffness when a human is nearby or in contact with the robot. The key point of the invention described here is a robot link made of an airtight chamber formed by a soft and flexible, but high-strain resistant combination of a plastic mesh and silicone wall. Inflated with air to a high pressure, the mesh-silicone chamber behaves like a rigid link; reducing the air pressure, softens the link and rendering the robot structure safe. This paper investigates a number of our link prototypes and shows the feasibility of the new concept. Stiffness tests have been performed, showing that a significant level of stiffness can be achieved - up to 40 N reaction force along the axial direction, for a 25 mm diameter sample at 60 kPa, at an axial deformation of 5 mm. The results confirm that this novel concept to linkages for robot manipulators exhibits the beam-like behaviour of traditional rigid links when fully pressurised and significantly reduced stiffness at low pressure. The proposed concept has the potential to easily create safe robots, augmenting traditional robot designs

A Multiplexed Sonomyography System for Proprioceptive Proportional Control of Biomechatronic Interfaces

Sonomyography is an ultrasound-imaging-based technique that measures muscle activity. Real-time imaging of deep-seated muscle activity enables robust and intuitive biomechatronic control. However, the form factor of clinical ultrasound systems limits the practical utility of sonomyography. Therefore, recent investigations aim towards developing wearable ultrasound systems to utilize sonomyography for biomechatronic interfacing. In this paper, a wearable, multiplexed sonomyography transducer array for real-time sensing muscle activity has been presented. The forearm-muscle activity was quantified using a computationally inexpensive, correlation-based metric to generate a sonomyography signal. The sonomyography signal was then used to perform a human-computer interaction-based target achievement task involving one degree of freedom control in real-time. Results show that participants achieved the targets with an average success rate of > 96 % for a target width of 10%, with minimal training. The results demonstrate the potential of a multiplexed sonomyography system for intuitive control of biomechatronic interfaces

Analysis of Comfort and Ergonomics for Clinical Work Environments

Work related musculoskeletal disorders (WMSD) are a serious risk to workers' health in any work environment, and especially in clinical work places. These disorders are typically the result of prolonged exposure to non-ergonomic postures and the resulting discomfort in the workplace. Thus a continuous assessment of comfort and ergonomics is necessary. There are different techniques available to make such assessments, such as self-reports on perceived discomfort and observational scoring models based on the posture's relevant joint angles. These methods are popular in medical and industrial environments alike. However, there are uncertainties with regards to objectivity of these methods and whether they provide a full picture. This paper reports on a study about these methods and how they correlate with the activity of muscles involved in the task at hand. A wearable 4-channel electromyography (EMG) and joint angle estimation device with wireless transmission was made specifically for this study to allow continuous, long-term and real-time measurements and recording of activities. N=10 participants took part in an experiment involving a buzz-wire test at 3 different levels, with their muscle activity (EMG), joint angle scores (Rapid Upper Limb Assessment - RULA), self-reports of perceived discomfort (Borg scale) and performance score on the buzz-wire being recorded and compared. Results show that the Borg scale is not responsive to smaller changes in discomfort whereas RULA and EMG can be used to detect more detailed changes in discomfort, effort and ergonomics

An Integrated Method for the Geometric Inspection of Wind Turbine Hubs with Industrial Robot

Wind turbine manufacturing requires the assembly of large mechanical components, which is crucial to inspect along the production line in order to prevent high reparation costs afterwards. A critical component in this process is the turbine hub, which supports the wind blades and ball bearings allowing the pitch motion. At present, hub inspection is a manual task, which requires expert operators and long execution time. This paper proposes a novel methodology for the selfadaptive inspection of wind turbine hubs via industrial robots: a set of Critical-To-Quality parameters (CTQs), are inferred from the CAD drawing of wind turbine hub; registration between robot and hub is performed; finally a CAD2robot trajectories planning is accomplished. Methodology is implemented through a Matlab and Simulink Programming Language and combined with an Industrial PC-based control technology Beckhoff TwinCAT 3. Tests with an Fanuc Industrial M-6iB robot arm and R-30iA controller have been successfully performed on re-scaled model of the hub. The flexibility of this methodology allows applications on other industrial contexts, which can benefit from automation

Towards Safer Obstacle Avoidance for Continuum-Style Manipulator in Dynamic Environments

The flexibility and dexterity of continuum manipulators in comparison with rigid-link counterparts have become main features behind their recent popularity. Despite of that, the problem of navigation and motion planning for continuum manipulators turns out to be demanding tasks due to the complexity of their flexible structure modelling which in turns complicates the pose estimation. In this paper, we present a real-time obstacle avoidance algorithm for tendondriven continuum-style manipulator in dynamic environments. The algorithm is equipped with a non-linear observer based on an Extended Kalman Filter to estimate the pose of every point along the manipulator’s body. A local observability analysis for the kinematic model of the manipulator is also presented. The overall algorithm works well for a model of a single-segment continuum manipulator in a real-time simulation environment with moving obstacles in the workspace of manipulators, able to avoid the whole body of manipulators from collision

Multi-axis Stiffness Sensing Device for Medical Palpation

This paper presents an innovative hand-held device able to compute stiffness when interacting with a soft object. The device is composed of four linear indenters and a USB camera. The stiffness is computed in real-time, tracking the movements of spherical features in the image of the camera. Those movements relate to the movements of the four indenters when interacting with a soft surface. Since the indenters are connected to springs with different spring constants, the displacement of the indenters varies when interacting with a soft object. The proposed multi-indenting device allows measuring the object's stiffness as well as the pan and tilt angles between the sensor and the surface of the soft object. Tests were performed to evaluate the accuracy of the proposed palpation mechanism against commercial springs of known stiffness. Results show that the accuracy and sensitivity of the proposed device increases with the softness of the examined object. Preliminary tests with silicon show the ability of the sensing mechanism to characterize phantom soft tissue for small indentation. It is noted that the results are not affected by the orientation of the device when probing the surface. The proposed sensing device can be used in different applications, such as external palpation for diagnosis or, if miniaturized, embedded on an endoscopic camera and used in Minimally Invasive Surgery (MIS)

A K-nearest clamping force classifier for bolt tightening of wind turbine hubs

A fuzzy-logic controller supporting the manufacturing of wind turbines and the bolt tightening of their hubs has been designed. The controller embeds assembly error recognition capability and detects tightening faults like misalignment, different threads, cross threads and wrong or small nuts. According to this capability, K-nearest classifiers have been implemented to cluster the output controllers into the diverse fault scenarios. Classifiers make use of the time of execution of the tightening process, the final angular position of and applied torque of the tightening tool, the resultant clamping force and possible combinations of those parameters. Two classes and five classes configurations are considered: classifiers are initially asked to discriminate between fault and no fault scenarios (e.g. two classes); then, five classes are considered according to five different fault situations (i.e. regular tightening, bolt misalignment, dissimilar threads of bolt and nut, missing nut and small bolt). Classifiers performances are estimated in terms of resubstitution and cross-validation loss. Confusion matrixes of actual and predicted classification are also evaluated for each classifier. The low computational cost of the proposed classifiers suggests directly implementing these algorithms on micro-controller and physical computing, which may be straight integrated within the tightening tool

Real-time Robot-assisted Ergonomics

This paper describes a novel approach in human robot interaction driven by ergonomics. With a clear focus on optimising ergonomics, the approach proposed here continuously observes a human user's posture and by invoking appropriate cooperative robot movements, the user's posture is, whenever required, brought back to an ergonomic optimum. Effectively, the new protocol optimises the human-robot relative position and orientation as a function of human ergonomics. An RGB-D camera is used to calculate and monitor human joint angles in real-time and to determine the current ergonomics state. A total of 6 main causes of low ergonomic states are identified, leading to 6 universal robot responses to allow the human to return to an optimal ergonomics state. The algorithmic framework identifies these 6 causes and controls the cooperating robot to always adapt the environment (e.g. change the pose of the workpiece) in a way that is ergonomically most comfortable for the interacting user. Hence, human-robot interaction is continuously re-evaluated optimizing ergonomics states. The approach is validated through an experimental study, based on established ergonomic methods and their adaptation for real-time application. The study confirms improved ergonomics using the new approach.Comment: 6 pages, accepted and to be presented at IEEE ICRA 201