Marcel Verner

Development of a sliding-leg tripod as an add-on device for manufacturing

This paper presents the work on developing a sliding-leg tripod as a programmable add-on device for manufacturing. The purpose is to enhance the capabilities of any machine by providing it with a more flexible range of motion. This device can be used as a toolhead for CNC machine tools and robots, or as a work stage for coordinate measuring machines and laser scanning systems. In this paper, system modelling, analysis and control of this device is presented. System modeling includes mobility study, kinematic model and inverse kinematics. System analysis includes workspace analysis, transmission ratio and stiffness analysis. System control includes path planning, joint space control and Cartesian space prediction. It is shown that the proposed device can provide flexibility and dexterity to machines.

Integrated Design Toolbox for Tripod-Based Parallel Kinematic Machines

This paper presents a concept and implementation of a toolbox for design and application of tripod-based parallel kinematic machines (PKMs). The toolbox is a suite of design tools to support users from conceptual design to actual application of tripod-based PKMs. These design tools have been individually developed in different languages and development environments, and are integrated seamlessly using a JAVA-based platform. Users can access all the design tools through a friendly graphical user interface (GUI). It is the first computer-aided design system specially developed for tripod-based PKMs. The toolbox includes some innovative methodologies, such as a forward kinematics solver, the concept of joint workspace, on-line monitoring based on forward kinematics, and the concept of motion purity. The paper gives an overview on the toolbox architecture and some key technologies.

Integrating Java 3D model and sensor data for remote monitoring and control

Abstract This paper presents a novel approach and a framework for web-based systems that can be used in distributed manufacturing environments. A prototype is developed to demonstrate its application to remote monitoring and control of a Tripod—one type of parallel kinematic machine. It utilizes the latest Java technologies (Java 3D and Java Servlets) as enabling technologies for system implementation. Instead of using a camera for monitoring, the Tripod is modeled using Java 3D with behavioral control nodes embedded. Once downloaded from its server, the 3D model behaves in the same way of its counterpart at client side. It remains alive by connecting with the Tripod through message passing, e.g., sensor signals and control commands transmissions. The goal of this research is to eliminate network traffic with Java 3D models, while still providing users with intuitive environments. In the near future, open-architecture devices will be web-ready having Java virtual machines embedded. This will make the approach more effective for web-based device monitoring and control.

Optimal Calibration of Parallel Kinematic Machines

In this paper, a new method for optimal calibration of parallel kinematic machines (PKMs) is presented. The basis of the methodology is to exploit the least error sensitive regions in the workspace to yield optimal calibration. To do so, an error model is developed that takes into consideration all the geometric errors due to imprecision in manufacturing and assembly. Based on this error model, it is shown that the error mapping from the geometric errors to the pose error of the PKM depends on the Jacobian inverse. The Jacobian inverse would introduce spurious errors that would affect the calibration results, if used without proper care. Hence, areas in the workspace with smaller condition numbers are selected for calibration. Simulations and experiments are presented to show the effectiveness of the proposed method. Calibration software based on the proposed method has been embedded in the tripod developed at the National Research Council of Canadas Integrated Manufacturing Technologies Institute.

Design optimization and remote manipulation of a tripod

A tripod is one type of parallel kinematic machine having three degrees of freedom. The sliding-leg tripod presented in this paper is designed as a programmable add-on device for manufacturing and shop floor automation. It can be used as a toolhead for machine tools, or as a work stage for coordinate measuring machines. Its purpose is to enhance the capability of a machine by providing it with a more flexible range of motion and controllability from any distance. As decentralization of manufacturing grows, shop floor equipment like this is required to become networkable and remotely accessible. This paper focuses on two separate issues: Tripod design optimization and its remote manipulation, including real-time monitoring and remote control of the tripod. A tripod prototype and a web-based software system are developed to verify the feasibility of the approach as well as the tripod accessibility in a distributed environment. It is shown that the proposed approach can improve the tripod design and its controllability. A large application potential of this approach is also predicted.

Error Sensitivity Analysis for Optimal Calibration of Parallel Kinematic Machines

In this paper, error sensitivity analysis is discussed for the purpose of optimal calibration of parallel kinematic machines (PKMs). The idea is to find a less error sensitive area in the workspace for calibration. To do so, an error model is developed that takes into consideration all the geometric errors due to imprecision in manufacturing and assembly. Based on this error model, it is shown that the error mapping from the geometric errors to the pose error of the PKM depends on the Jacobian inverse. The Jacobian inverse would introduce spurious errors that would affect the calibration results, if used without proper care. Hence, it is suggested to select the areas in the workspace with smaller condition numbers for calibration. A case study is presented to illustrate the proposed method.Copyright

A Toolbox for Tripod Design, Simulation, and Monitoring

The paper presents a concept and implementation of a toolbox for the design and application of the tripod-based parallel kinematic machines (PKMs). The toolbox is a suite of design tools to support the users from the conceptual design to the actual application of the tripod-based PKMs. These design tools have been individually developed in different languages and they are integrated seamlessly using a Java-based platform. Users can access all of the design tools through a user-friendly graphical interface. It is the first computer-aided design system specially developed for tripod-based PKMs. The toolbox includes some implementations of our innovative methodologies, such as a forward kinematics solver, the concept of joint workspace analysis, on-line monitoring based on forward kinematics, and the concept of motion purity analysis. The paper gives an overview on the toolbox architecture, GUI, and some key technologies.Copyright

Design and Implementation of a PKM Based 5-Axis Reconfigurable Machine

In this paper we present the design and implementation of a parallel kinematics based reconfigurable machine. The machine utilizes a Tripod based module with 3 degrees-of-freedom combined with a linear X-Y stage and gantry system for 5-axis machining. The tripod module uses a unique passive link mechanism with constant length leg actuators. This architecture offers good stiffness and high accuracy. The gantry system itself is reconfigurable, allowing for changing the working characteristics of the machine. The control system is based on open architecture principles. Corresponding to the mechanical reconfiguration, the control system also needs to be reconfigured to reflect the actual state of the machine. Mechanical reconfiguration also brings with it the need to verify the accuracy of the new configuration. Also discussed in the paper is the calibration methodology that ensures high production quality in each configured mode of the machine.Copyright