Stiffness modeling of robotic manipulator with gravity compensator

The paper focuses on the stiffness modeling of robotic manipulators with gravity compensators. The main attention is paid to the development of the stiffness model of a spring-based compensator located between sequential links of a serial structure. The derived model allows us to describe the compensator as an equivalent non-linear virtual spring integrated in the corresponding actuated joint. The obtained results have been efficiently applied to the stiffness modeling of a heavy industrial robot of the Kuka family

Compliance error compensation in robotic-based milling

The paper deals with the problem of compliance errors compensation in robotic-based milling. Contrary to previous works that assume that the forces/torques generated by the manufacturing process are constant, the interaction between the milling tool and the workpiece is modeled in details. It takes into account the tool geometry, the number of teeth, the feed rate, the spindle rotation speed and the properties of the material to be processed. Due to high level of the disturbing forces/torques, the developed compensation technique is based on the non-linear stiffness model that allows us to modify the target trajectory taking into account nonlinearities and to avoid the chattering effect. Illustrative example is presented that deals with robotic-based milling of aluminum alloy

Workspace optimisation of a reconfigurable parallel kinematic manipulator

One significant limitation of parallel kinematic machines in the past has been the limited workspace to installation space ratio. The Gantry-Tau is an example of a relatively new PKM which improves this ratio by allowing a change of assembly mode without internal link collisions or collisions between the links and the moving TCP platform. The avoidance of these internal collisions is made possible by using a triangular-mounted link pair. This paper introduces for the first time the unreachable workspace for the Gantry-Tau. The unreachable area can occur in the middle of the workspace of reconfigurable PKMs with fixed length actuators. It is important to eliminate unreachable areas when designing the Gantry-Tau PKM because they appear in the middle of the workspace which is often the most useful part of the workspace. A geometric approach which describes both the reachable and unreachable workspace has been developed. This approach is significantly faster than analytical workspace calculation methods based on the inverse kinematics. Because of the fast computational speed of the geometric approach presented in this paper, the method is an ideal candidate for inclusion in a design optimisation framework. An optimised kinematic design of the Gantry-Tau is presented in the paper

Kinematic optimisation of the gantry-tau parallel kinematic manipulator with respect to its workspace

The Gantry-Tau is a recently developed parallel kinematic manipulator (PKM). Since the actuators are stationary it possesses the following characteristics: high speed, high acceleration, small moving mass and high static and dynamic accuracy. Since all link forces in the structure are axial, high stiffness can also be achieved. One of the main advantages of the Gantry-Tau machine is a large workspace area in comparison with traditional parallel machines. However, parameters of the machine, such as link lengths and dimension of support frames, can be difficult to design manually. In this paper we present a method to optimise such parameters to achieve the largest possible workspace. The problem is solved by using a non-linear optimization routine and imposing the parameterization on the midpoints of three spheres generated by the parallel links that intersect at the tool center point (TCP)

Hard material small-batch industrial machining robot

Hard materials can be cost effectively machined with standard industrial robots by enhancing current state-of-the-art technologies. It is demonstrated that even hard metals with specific robotics-optimised novel hard-metal tools can be machined by standard industrial robots with an improved position-control approach and enhanced compliance-control functions. It also shows that the novel strategies to compensate for elastic robot errors, based on models and advanced control, as well as the utilisation of new affordable sensors and human-machine interfaces, can considerably improve the robot performance and applicability of robots in machining tasks. In conjunction with the development of safe robots for human-robot collaboration and cooperation, the results of this paper provide a solid background for establishing industrial robots for industrial-machining applications in both small- and medium-size enterprises and large industry. The planned short-term and long-term exploitation of the results should significantly increase the future robot usage in the machining operations