Design and Kinematic Analysis of a Novel 2-DoF Closed-Loop Mechanism for the Actuation of Machining Robots

The essential characteristics of machining robots are their stiffness and their accuracy. For machining tasks, serial robots have many advantages such as large workspace to footprint ratio, but they often lack the stiffness required for accurately milling hard materials. One way to increase the stiffness of serial manipulators is to make their joints using closed-loop or parallel mechanisms instead of using classical prismatic and revolute joints. This increases the accuracy of a manipulator without reducing its workspace. This paper introduces an innovative two degrees of freedom closed-loop mechanism and shows how it can be used to build serial robots featuring both high stiffness and large workspace. The design of this mechanism is described through its geometric and kinematic models. Then, the kinematic performance of the mechanism is analyzed, and a serial arrangement of several such mechanisms is proposed to obtain a potential design of a machining robot.

Auto-Calibration for Vision-Based 6-D Sensing System to Support Monitoring and Health Management for Industrial Robots

Industrial robots play important roles in manufacturing automation for smart manufacturing. Some high-precision applications, for example, robot drilling, robot machining, robot high-precision assembly, and robot inspection, require higher robot accuracy compared with traditional part handling operations. The monitoring and assessment of robot accuracy degradation become critical for these applications. A novel vision-based sensing system for 6-D measurement (six-dimensional x, y, z, yaw, pitch, and roll) is developed at the National Institute of Standards and Technology (NIST) to measure the dynamic high accuracy movement of a robot arm. The measured 6-D information is used for robot accuracy degradation assessment and improvement. This paper presents an automatic calibration method for a vision-based 6-D sensing system. The stereo calibration is separated from the distortion calibration to speed up the on-site adjustment. Optimization algorithms are developed to achieve high calibration accuracy. The vision-based 6-D sensing system is used on a Universal Robots (UR5) to demonstrate the feasibility of using the system to assess the robot’s accuracy degradation.

Stiffness Evaluation of an Adsorption Robot for Large-scale Structural Parts Processing

Efficient and economical processing of large-scale structural parts is in increasing need and is also a challenging issue. In this paper, an adsorption machining robot for processing of large-scale structural parts is presented. It has potential advantages in flexible, efficient and economical processing of large-scale structural parts because of the adsorption ability. Stiffness is one of the most important performance for machining robots. In order to investigate the stiffness of the robot in the workspace, the kinematics of the adsorption manipulator, the five-axis machining manipulator and the adsorption machining robot is derived step by step. Then with the help of Finite Element Analysis (FEA), a stiffness modeling method considering the compliance of the base is proposed. A stiffness isotropy index is put forward to evaluate the robot's overall stiffness performance by taking all possible working conditions into consideration. Based on the index, stiffness evaluation in the reachable workspace is carried out and an optimized workspace is identified considering the overall stiffness magnitude, stiffness isotropy and workspace volume, which will be used in the machining process. The stiffness modeling method and stiffness isotropy index proposed in the paper are universal and can be applied to other parallel robots.

Optimizing OCTG Thread Manufacturing Operation Using Automation

The paper discusses a unique technique developed initially at Nation Institute of Technology, Surat that is remodeled in real-world applications. The concept consists primarily of a user-friendly software facilitating direct communication with any intelligent or learning system/robot operating under known parameters of motor specifications. Any software base permitting high level PC interface without ASCII interrupt can be used for easy programming. This allows for a learning operation mode where a prevention of time lag is enabled by stored machine data, captured through movements such movements can be physically made or taught via programs to the device and such learning aspects make the machine more efficient where the robot can either perform individual actions as needed or learn new methods for the same results and can perform a series of actions continuously. Using the stored data, the machine is also capable of autonomous movements based on the path of least resistance as calculated by the time it takes to perform an act. Interfacing Technique Tool Machining Robot (ITTMR) was developed as robotic tool holder that can determine the shape and size of different OCTG pipes utilized in the downhole industry and enable it to machine appropriate threads on the pipe with no manual intervention. The process thereby completely negates any possibility of human error which can otherwise cause heavy loss on finished equipment that are rendered unusable because of threading errors on almost nearly finished complex milled parts or assemblies that are pending threads as the final operation. The purpose of the software codes is to provide a user-friendly GUI that can communicate with any machine by pulling in appropriate ACNC programs and performing the required tasks associated with the operating system and specifications of the motors/mobilization equipment’s used. For the purpose of this paper, the software code is not provided. Any firmware base that permits the usage of an ASCII interrupt can be used and for the purpose of this operation, an RS323 equivalent board will also suffice for basic operations, however a complex ITTMR system has been utilized. This paper solely addresses the technique of how the threading operation is performed and does not address the process of how the pipe is bought to the machine or other associated aspects of the software to retain any possible patent applications on the same.

Single Degree-of-Freedom Modeling of the Nonlinear Vibration Response of a Machining Robot

Highly dynamic machining forces can cause excessive and unstable vibrations when industrial robots are used to perform high-force operations such as milling and drilling. Implementing appropriate optimization and control strategies to suppress vibrations during robotic machining requires accurate models of the robot’s vibration response to the machining forces generated at its tool center point (TCP). The existing models of machining vibrations assume the linearity of the structural dynamics of the robotic arm. This assumption, considering the inherent nonlinearities in the robot’s revolute joints, may cause considerable inaccuracies in predicting the extent and stability of vibrations during the process. In this article, a single degree-of-freedom (SDOF) system with the nonlinear restoring force is used to model the vibration response of a KUKA machining robot at its TCP (i.e., machining tool-tip). The experimental identification of the restoring force shows that its damping and stiffness components can be approximated using cubic models. Subsequently, the higher-order frequency response functions (HFRFs) of the SDOF system are estimated experimentally, and the parameters of the SDOF system are identified by curve fitting the resulting HFRFs. The accuracy of the presented SDOF modeling approach in capturing the nonlinearity of the TCP vibration response is verified experimentally. It is shown that the identified models accurately predict the variation of the receptance of the nonlinear system in the vicinity of well-separated peaks, but nonlinear coupling around closely spaced peaks may cause inaccuracies in the prediction of system dynamics.