Showing papers in "Robotics and Computer-integrated Manufacturing in 1992"

Resist process system

Abstract: A resist process system of the present invention includes at least two robots for conveying a wafer, a passage through which the robots can move, plural process units arranged along the passage, and a waiting unit for temporarily holding the wafer which is to be processed. The waiting unit is arranged beside the passage and between the process units and it includes plural compartments partitioned in it.

Neural network solution for the forward kinematics problem of a Stewart platform

Abstract: A multiple neural network structure called cascaded CMAC (cerebella model arithmetic computer) is proposed to solve the forward kinematics problem of a (parallel link manipulator, called a Stewart platform. The cascaded CMAC networks can provide faster learning and the ability to capture both general trends and fine details of unknown nonlinear mapping. The performance of the cascaded CMAC network is compared with the backpropagation network for the same problem, and the results show that the proposed network is able to learn much faster than the backpropagation net. >

Position indicator for a piston controlled robot part

Abstract: A piston-cylinder assembly is equipped with means for determining and validating the piston position of that assembly part of a robot. A piston 1 slides axially in a cylinder 2, and moves a permanent magnet 13. The resulting magnetic field is sensed by a Hall effect transistor. A member 12 is controlled by a program of analog signals coming from the sensor. When the run of piston 1 is stopped, the position of that piston is one of the positions that have been previously determined and memorized by control member 12.

Automatic inspection planning within a feature-based CAD system

Abstract: This paper describe a CIM system which incorporates automatic generation of inspection on plans for coordinate measuring machines (CMMs). Design is done in terms of form features. Associated with each feature are inspection plan fragments (IPFs) which are instances of inspection procedures. There are three basic types of plan fragments for CMMs: (1) fragments for checking the internal dimensions of a feature, (2) fragments for checking the relationships between features, and (3) modified fragments for use when the feature to be inspected intersects another feature. Using this approach, a list of suitable inspection points and approach vectors is generated. A path planner then combines the elements of the list to produce a valid inspection path for the CMM. The system is consistent with the accepted ANSI Y14.5M standard for dimensioning and tolerancing as well as with observed industrial practice.

Research laboratory for fish processing automation

Abstract: This paper outlines the organization, resources, and research and development activities of a newly established laboratory for industrial automation at a major Canadian university. The laboratory has been established in the Department of Mechanical Engineering primarily to support the research and development activities associated with the Natural Sciences and Engineering Research Council (NSERC) Chair of Industrial Automation. The research is focused on the development of advanced and low-cost technology for flexible automation of the fish processing industry. The main objective is to upgrade the technology used in the mechanical processing of fish, thereby reducing wastage of the primary product, improving efficiency, and making the local industry more competitive in export markets. Establishment of an infrastructure in industrial automation within the university and local training/ retraining of engineers with control and automation expertise for local industries are related objectives. As a specific task, an experimental workcell for fish processing is being developed in the laboratory. The theme of the activities of the laboratory is the integration of advanced control, high-level computer vision, and robotic manipulation and devices, for application in the area of fish processing.

Robot calibration using the CPC error model

Abstract: The complete and parametrically continuous (CPC) robot kinematic modeling convention has no model singularities and allows the modeling of the robot base and tool in the same manner by which the internal links are modeled. These two properties can be utilized to construct robot kinematic error models employing the minimum number of kinematic error parameters. These error parameters are independent and span the entire geometric error space. The BASE and TOOL error models are derived as special cases of the regular CPC error model. The CPC error model is useful for both kinematic identification and kinematic compensation. This paper focuses on the derivation of the CPC error models and their use in the experimental implementation of robot calibration.

Static modeling and control of redundant manipulators

Abstract: This paper develops unified static models for control of a redundant manipulator. We introduce the Premultiplier Diagram to describe the static behavior of a redundant manipulator. This diagram provides insight into the algebra and physics related to redundant manipulators. We derive redundancy expressions for the joint displacement, joint torque and joint stiffness matrix. These redundancy expressions are composed of a particular (net) part and a homogeneous (null) part. Based on the orthogonality property between the net and the null components, we propose an extension of the stiffness control scheme for redundant manipulators. We also show how the decomposed and decoupled static behavior of redundant manipulators can be used to derive an optimal control strategy.

On controlling robots with redundancy

Abstract: Recently there has been considerable interest in increasing the applicability and utility of robots by developing manipulators which possess kinematic and/or actuator redundancy. This paper presents a unified approach to controlling these redundant robots. The proposed control system consists of two subsystems: an adaptive position controller which generates the Cartesian-space control force F ϵR m required to track the desired end-effector position trajectory, and an algorithm that maps this control input to a robot joint torque vector T ϵR n . The F → T map is constructed so that the robot redundancy (kinematic and/or actuator) is utilized to improve the performance of the robot. The control scheme does not require knowledge of the complex robot dynamic model or parameter values for the robot or the payload. As a result, the controller is very general and is computationally efficient for on-line implementation. Computer simulation results are given for a kinematically redundant robot, for a robot with actuator redundancy, and for a robot which possesses both kinematic and actuator redundancy. In each case the results demonstrate that accurate end-effector trajectory tracking and effective redundancy utilization can be achieved simultaneously with the proposed scheme.

Feedback linearization control of flexible joint robots

Abstract: In this paper, the control of a two link, flexible joint manipulator is examined. Among external forces, an exogenous constraint force acting on the end-effector is included. The manipulator dynamics are described by: x =ƒ( x )+ g(x)u +J T ( x )ƒ e ( x ) . On the assumption that f (x), g (x) and J T f e (x) are smooth vector fields, it is shown that the inner loop control u is of the form: u = 1 〈dT n ,g〉 ( v −〈dT n ,(ƒ( x )+J T ƒ e ( x ))〉) where u is an outer loop control signal and y = T (x) is a diffleomorphism that transform (a) into linear system. As the position control scheme is adopted, the value of the contact force is not controlled. The results for the inner loop control are substantiated by simulation of a two-link robot model. The robustness of the control method is examined and a Lyapunov-based control correction, similar to that of the free motion case, is implemented. Results are obtained for parametric errors of up to 50%. In the simulation, the manipulator is required to follow a specified joint trajectory such that the end-effector traces a sinusoidal path along a constraint surface. The results obtained illustrate the tracking of the link reference trajectory and indicate that the inner loop corrections are valid.

Force and motion control of a single flexible manipulator link

Abstract: The problem of controlling the contact force exerted by the tip of a structurally flexible manipulator link on its environment is addressed. Control strategies which employ an adaptive long range predictive control algorithm based on the generalized predictive control (GPC) algorithm of Clarke et al. (Automatica, 23(2): 137–148, 1987) are developed and demonstrated. A simulation of a single flexible manipulator link contacting a deformable surface has been utilized to evaluate the control strategies. The simulation includes a beam-type continuum model of the manipulator link and a lumped-parameter model of the surface dynamics in the region of contact. Simulation results are presented which demonstrate the performance of an adaptive version of the force controller. The controller is adaptive in the sense that the system model is identified on-line using a recursive least squares (RLS) algorithm. Also presented are some results and a discussion on the problem of achieving stable force control after a contact event in which the link has a significant approach velocity. A control strategy which uses sensor information to predict the initial contact force transient and temporarily modifies the force setpoint during this transient is proposed and demonstrated in simulation.

State observers for rigid and elastic joint robots

Abstract: This paper refers to the design of nonlinear observers for robot manipulators. Robots without and with elasticity in the joints are analyzed. In both cases, the uniform asymptotic stability of the error dynamics is proved and some separation and robustness properties are derived. The observer design is accomplished by exploiting the structural properties of the robot dynamics. The proposed observation algorithms have no need of coordinate changes, thus simplifying the observer implementation.

Automation of surface finishing processes

Abstract: The development of robots capable of interacting dynamically with the environment has proven to be a difficult task. Since a majority of manufacturing tasks require interaction of robots with their environment, this has become an important focus for research in the industry. Solutions both to specific manufacturing operations and to the theoretical body of knowledge within the industry are extremely important. The interaction of the robot with its environment is investigated in this paper for the configuration of a quick actuator and sensor attached to the robot tool. This configuration has been tested in an industrial application for Steinway & Sons, the world renowned piano manufacturer, specifically for the automation of the labor-intensive rubbing and finishing operations. The robot architecture utilizes a combination of macro-micro manipulator to improve its response time. A quick actuator added to the end of the robot arm is the micromanipulator, and the robot arm is the macromanipulator. Force and impedance control laws are executed concurrently by two separate controllers to control the quick actuator and the robot arm respectively. The experimental system proves the ability of this configuration to follow the complex contour of a grand piano rim and to exert a given force while rubbing its surface.

Economic analysis of robotic operations: A case study of a thermal spraying robot

Abstract: There is growing interest in the industrial applications of computer-integrated manufacturing (CIM) and robotic technology. The economic analysis methods which are currently available to assess the cost effectiveness of robotic systems are, however, limited. This paper presents a methodology to address this issue. To demonstrate the methodology, a case-study is presented which uses a thermal spraying robot in a rapid tool manufacturing system. The interdependencies between tolerance, robot accuracy, and the probability of a successful spraying operation are demonstrated. The economic effects of using robots in the spraying process are analyzed. Analytical models are developed to estimate the productivity of components without any defects and the improvement in tool life attributable to robotic spraying. The economic analysis method presented in the paper is also applicable to other operations such as robotic assembly and robotic welding.

Control of flexible joint robots

Abstract: In this paper we describe a switching control scheme for flexible joint robots which does not use link jerk or acceleration feedback. Our control scheme does not require the numerical differentiation of the velocity signal or the inversion of the inertial matrices. Simulations are presented to verify the validity of the control scheme and its superiority over existing rigid robot controllers when applied to flexible joint robots with extremely flexible joints.

Experimental and statistical determination of the static position repeatability and a recommended specification for a SCARA robot

Abstract: This paper describes an experiment and the statistical analysis performed to evaluate the repeatability of a SCARA robot and proposes an alternative form of specification for repeatability. Repeatability has been chosen because the precision obtained from teach-and-play-back programming for pick-and-place tasks, which is still widely used, depends primarily upon this performance value. The measuring method uses two theodolites, which though laborious in set-up is nevertheless simple, economical and sufficiently accurate for the purpose intended. The results are used for comparison with the given specification and for studying the influence of factors such as load, speed and spatial location in the working envelope using analysis of variance; the estimate of the repeatability value is calculated using the standard deviations of the measured coordinates of representative points modified by a factor from Student's t curves. From the analysis, it can be inferred that the repeatability value is dependent upon operating speed, load and plane location. The experimental study also points to a possible form of specification. For example, for the specification to be useful in the study of arrangement of feeders of parts to be assembled by the robot and the estimation of throughput given part weight, it could be given in a table form showing the range of the repeatability value for the designed combinations of speed, payload and position in the envelope.

Inter enterprise CIM—a mechanism for graduate education

Abstract: The successful harnessing of information technology in the pan national manufacturing environment demands a new response in the provisioning of the key integrated business resource—personnel. The CIM Institute has defined and built a teaching and research environment which focuses attention on the business process including the increasingly important semi-externalized business processes. Projects and research are undertaken which study the complexity of information management in supply chains. Networking with other universities and companies is establishing an environment close to the leading edge of industrial need. The paper presented describes the rationale for the current work of the CIM Institute and its direction in delivering both people and process for inter enterprise CIM development.

Modelling automated manufacturing systems using a modification of coloured petri nets

Abstract: Automated manufacturing systems (AMS) are a class of systems exhibiting concurrency, asynchronicity and distributedness, and can be modelled using Petri nets. The advantage of using Petri nets is that they provide graphical models, with formal methods of analysis. However, graphical representation of Petri net models becomes difficult even for medium-sized systems since such graphs tend to become inconveniently large. Coloured Petri nets (CPN) are a variant which enables a more concise representation with the same modelling power. This paper develops a model for simulation of AMS whose correctness can be formally established, and which can be graphically represented and visually understood. It presents a modelling approach for AMS, based on a modified version of CPN, with enhanced modelling power. The proposed modifications result in highly compact graphical representations, and also render the model dynamic , i.e. capable of changing dynamically to reflect currently selected system parameters. These features make the proposed model ideally suited for discrete event simulation.

A configuration independent error model of machine tools: Hyperpatch model and metrology pallet

Abstract: A machine tool error model based on a three-dimensional hyperpatch error map was developed to describe the machine tool error field over a workspace. The error map was generated by a set of measurement points without using a detailed relationship among joints and linkages of a machine tool. The modeling is based on the motion that an ideal workspace is distorted to an actual workspace through a prescribed parametric representation. The concept was implemented on a three-axis CNC machining center. A metrology pallet was designed to serve as a reference coordinate frame of the workspace. A touch trigger probe was used to collect the required data. Experimental results show that this error model is capable of modelling the warm machine tool distortion behavior. The proposed model is based on the observed phenomena rather than the structural configuration of machine tools. Therefore, the advantage of this approach is that only a few measurements are required to construct the prediction model for a variety of machine tool configurations and for working environments.

Feasibility study of fuzzy control systems in machining processes

Abstract: A new on-line force control algorithm was developed in machining operations by using fuzzy set theory. A simulation study was carried out in machining operations to verify the effectiveness of the proposed control system for the improvement of productivity based on experimental data. Fuzzy control logic proved very successfully in analyzing uncertain and complex systems which cannot be defined explicitly by mathematical tools because of properties such as multi input-multi output, non-linearity, time delay, etc. Also, the computation task and time is enormously reduced as compared to classical or modern control theory. Hence, it is possible to have real-time control of processes.

Toward a rational workholding methodology.

Abstract: The technology of workholding is intimately related to the developing surface features of the parts to be held, the tooling systems which generate these surfaces, and the approaches applied to grasp and secure the part. A rationale for workholding is developed which considers “single setup” as a desirable goal in the context of a machining FMS. A taxonomy of workholding is outlined with examples.

A CAD-based error mapping and layout facility for precision robotic operations

Abstract: This paper describes development of a kinematic error mapping and layout facility for precision robotic operations such as a tight-tolerance assembly. The facility is based on a CAD System which models the robot geometry and allows robot models and associated equipment to be positioned into a working arrangement and viewed in three dimensions, along with the working envelope of the robot. Both nonlinear and linearized models are used, in conjunction with the CAD database, to predict the distribution of the end-effector errors over the working volume. The 3D error distribution is then displayed in terms of an error map, such that the spot(s) with the minimum error in a sense consistent with the nature of an operation can be chosen to carry out the operation or the robotic cell layout is altered. The facility is based ·on a \"low cost\" CAD package (AutoCAD) suitable for operation on a personal computer and the built-in AutoLisp language is fully made used of to automate graphics and facilitate error model calculations. The functionality of the system is illustrated with reference to a revolute 4-axis robot, and the development of a robotic material handling workcell. It is shown that using the facility not only reduces the technique risks one may encounter during the time-consuming trial and errors, but also makes possible extensive evaluations and compromises among various options which is essential in the layout and plamiing phase.

Performance evaluation of real-time decision-making architectures for computer-integrated manufacturing systems

Abstract: A general method is proposed for the performance evaluation of a decision-making architecture for computer-integrated manufacturing systems. A decision-making architecture broadens the concept of a control architecture by integrating control, communication and database functions. A modular modeling methodology is developed that captures these features and is applicable to an arbitrary computer-integrated manufacturing architecture. The model is based on generalized stochastic Petri nets and leads to a quantitative evaluation of such performance measures as response time, average utilization of a particular system component, average queue length, etc. The net result is a design tool that can be used to make tradeoffs among the system parameters. The proposed technique is demonstrated using several real-time decision-making architectures. Several general conclusions are drawn from this investigation. Finally, a Petri net model reduction method is presented for this problem and used to compare the original performance evaluation results with those obtained from the simplified models.

Force control of robotic manipulators with structured uncertainties using variable structure control

Abstract: A discrete variable structure tracking controller is developed for a wide class of linear and nonlinear systems with structured uncertainties. The proposed controller uses a pole placement controller as a kernel and compensates for the errors associated with uncertainties. The algorithm is computationally efficient and can be easily used as a robust backup controller for the higher performance, but sensitive, adaptive algorithms.

Task decomposition and plan generation in multiagent domains

Abstract: This paper discusses the problem of finding assignment of subtasks to agents which generate concurrent and synchronized plans to achieve the main task in minimum time. An approach is discussed wherein an initial plan is generated containing the basic inherent operations and their sequences, using a specific assignment of subtasks. The initial plan is then to estimate the multiagent plans and their completion time for each assignment of subtasks in order to identify the optimal assignment. A method used by this approach to generate the initial plan is also described. This approach is analyzed and compared with the exhaustive method of generating plans for all possible assignments of subtasks to agents.

CIM in higher education: overview, industry perspective

Abstract: The results of this industry/higher education interaction are most positive, providing very significant benefits to both parties. The receptivity and cooperation of higher education to work closely with industry are proving to be an interesting phenomenon. Most significant will be the enhancement of CIM programs now taking place, which have the potential to better prepare individuals to both effect and move into tomorrow's computer-integrated enterprises.

Robust adaptive controller design for flexible joint manipulators

Abstract: In this paper the control problem for robot manipulators with flexible joints is considered. A reduced-order flexible joint model is constructed based on a singular perturbation formulation of the manipulator equations of motion. The concept of an integral manifold is utilized to construct the dynamics of a slow subsystem. A fast subsystem is constructed to represent the fast dynamics of the elastic forces at the joints. A composite control scheme is developed based on on-line identification of the manipulator parameters which takes into account the effect of certain unmodeled dynamics and parameter variations. Stability analysis of the resulting closed-loop full-order system is presented. Simulation results for a single link flexible joint manipulator are given to illustrate the applicability of the proposed algorithm.

New techniques applied to adaptive controlled machining

Abstract: The future capital intensive CIM and FMS systems will demand adaptive controlled (AC) machine tools. At the Department of Production Engineering of the Royal Institute of Technology in Stockholm (IMT/KTH) we are continuing the development of an advanced AC turning center. Our approach is to design and use sophisticated sensor systems to measure several features both on-line and off-line in order to obtain sufficient information on the cutting process and make adaptive feedback feasible. The AC system operates at three different levels: advanced process monitoring adaptive control constraint (ACC) adaptive control optimization (ACO). In this paper we give an overview of practical progress and improvements that have been achieved since our contribution to MSTF '87 in Cambridge.1 This includes: a new flexible sensor installation for optical tool wear measurements on-line tool wear estimation based upon a dynamic force sensor applied time series analysis for on-line chatter control real-time control of maching conditions with respect to cutting forces distributed real-time computer system solution.