Critically fast pick-and-place with suction cups

Fast robotics pick-and-place with suction cups is a crucial component in the current development of automation in logistics (factory lines, e-commerce, etc.). By "critically fast" we mean the fastest possible movement for transporting an object such that it does not slip or fall from the suction cup. The main difficulties are: (i) handling the contact between the suction cup and the object, which fundamentally involves kinodynamic constraints; and (ii) doing so at a low computational cost, typically a few hundreds of milliseconds. To address these difficulties, we propose (a) a model for suction cup contacts, (b) a procedure to identify the contact stability constraint based on that model, and (c) a pipeline to parameterize, in a time-optimal manner, arbitrary geometric paths under the identified contact stability constraint. We experimentally validate the proposed pipeline on a physical robot system: the cycle time for a typical pick-and-place task was less than 5 seconds, planning and execution times included. The full pipeline is released as open-source for the robotics community.Comment: 7 pages, 5 figure

Robotic manipulation of a rotating chain

This paper considers the problem of manipulating a uniformly rotating chain: the chain is rotated at a constant angular speed around a fixed axis using a robotic manipulator. Manipulation is quasi-static in the sense that transitions are slow enough for the chain to be always in "rotational" equilibrium. The curve traced by the chain in a rotating plane -- its shape function -- can be determined by a simple force analysis, yet it possesses complex multi-solutions behavior typical of non-linear systems. We prove that the configuration space of the uniformly rotating chain is homeomorphic to a two-dimensional surface embedded in $\mathbb{R}^3$. Using that representation, we devise a manipulation strategy for transiting between different rotation modes in a stable and controlled manner. We demonstrate the strategy on a physical robotic arm manipulating a rotating chain. Finally, we discuss how the ideas developed here might find fruitful applications in the study of other flexible objects, such as elastic rods or concentric tubes.Comment: 12 pages, 9 figure

Time-Optimal Path Tracking via Reachability Analysis

Given a geometric path, the Time-Optimal Path Tracking problem consists in finding the control strategy to traverse the path time-optimally while regulating tracking errors. A simple yet effective approach to this problem is to decompose the controller into two components: (i)~a path controller, which modulates the parameterization of the desired path in an online manner, yielding a reference trajectory; and (ii)~a tracking controller, which takes the reference trajectory and outputs joint torques for tracking. However, there is one major difficulty: the path controller might not find any feasible reference trajectory that can be tracked by the tracking controller because of torque bounds. In turn, this results in degraded tracking performances. Here, we propose a new path controller that is guaranteed to find feasible reference trajectories by accounting for possible future perturbations. The main technical tool underlying the proposed controller is Reachability Analysis, a new method for analyzing path parameterization problems. Simulations show that the proposed controller outperforms existing methods.Comment: 6 pages, 3 figures, ICRA 201

A New Approach to Time-Optimal Path Parameterization based on Reachability Analysis

Time-Optimal Path Parameterization (TOPP) is a well-studied problem in robotics and has a wide range of applications. There are two main families of methods to address TOPP: Numerical Integration (NI) and Convex Optimization (CO). NI-based methods are fast but difficult to implement and suffer from robustness issues, while CO-based approaches are more robust but at the same time significantly slower. Here we propose a new approach to TOPP based on Reachability Analysis (RA). The key insight is to recursively compute reachable and controllable sets at discretized positions on the path by solving small Linear Programs (LPs). The resulting algorithm is faster than NI-based methods and as robust as CO-based ones (100% success rate), as confirmed by extensive numerical evaluations. Moreover, the proposed approach offers unique additional benefits: Admissible Velocity Propagation and robustness to parametric uncertainty can be derived from it in a simple and natural way.Comment: 15 pages, 9 figure

Job Satisfaction and Its Relationships with Age, Gender and Educational Background in a Vietnamese Context : A thesis presented in partial fulfilment of the requirement for the degree of Master of Business Studies (Management) at Massey University, Manawatu New Zealand

The present study aims at examining the reliability and validity of a Vietnamese version of the Job Satisfaction Survey (JSS) which was developed by Spector (1997). It also reveals the current overall job satisfaction and investigates the relationship between job satisfaction and age, gender, and educational background among a specific community, the auditors and ex-auditors in Vietnam. With these goals, a quantitative cross-sectional design has been employed for the research. A pilot study with 68 Vietnamese respondents establishes a solid foundation for the final Vietnamese-translated version of the JSS. In the main study, a sample of 202 Vietnamese auditors and ex-auditors is recruited. The JSS in Vietnamese demonstrates a high internal consistency with the Cronbach’s alpha coefficient of α = .91. Moreover, an exploratory factor analysis reports an underlying construct of nine dimensions, which is similar to the original version of the JSS. The convergent and divergent validity of the scale are also analysed and return satisfactory results. The present research suggests that the auditors and ex-auditors in Vietnam are generally satisfied with their jobs and, surprisingly, the auditors are reported to be happier than their ex-colleagues in every job aspect. There is no relationship found between the overall job satisfaction and age or gender for this specific community, while a significant correlation between job satisfaction and educational background is confirmed. However, the women of this community are reported to be more likely to experience a lower level of job satisfaction when they get older or when they have a better educational background. The present study provides audit companies in Vietnam with recommendations for improving the job satisfaction of their employees. Its findings suggest that these firms should pay more attention to their older female employees as well as the ones with higher educational backgrounds due to their vulnerability to a lower level of job satisfaction than the opposite gender. Furthermore, directions and indications for future research are also offered in the present dissertation