Greg R. Luecke

Modeling and Designing a Hydrostatic Transmission With a Fixed-Displacement Motor

This study develops the dynamic equations that describe the behavior ofa hydrostatic transmission utilizing a variable-displacement axial-piston pump with a fixed-displacement motor. In general, the system is noted to be a third-order system with dynamic contributions from the motor, the pressurized hose, and the pump. Using the Routh-Hurwitz criterion, the stability range of this linearized system is presented. Furthermore, a reasonable control-gain is discussed followed by comments regarding the dynamic response of the system as a whole. In particular, the varying of several parameters is shown to have distinct effects on the system rise-time, settling time, and maximum percent-overshoot.

Dynamic simulation of virtual mechanisms with haptic feedback using industrial robotics equipment

This paper explores using industrial robotics equipment in a haptic (or kinesthetic) force display system conceived for mechanism design applications. The dynamics and kinematics of an aircraft flight control column/wheel are simulated as a human interacts directly with the end effector of a commonly available robotic manipulator. An admittance control paradigm is used for developing a haptic system wherein realistic simulation of the dynamic interaction forces between a human user and the simulated virtual object or mechanism is required. Experimental results are presented which demonstrate human user interaction with the virtual mechanism.

Virtual clay modeling using the ISU exoskeleton

A deformable non-uniform rational B-spline (NURBS) based volume is programmed for the Iowa State University (ISU) force-reflecting exoskeleton haptic device. A direct free-form deformation (DFFD) technique is applied for realistic manipulation. In order to implement real-time deformation, a nodal mapping technique is used to connect points on the virtual object with the NURBS volume. This geometric modeling technique is ideally incorporated with the force-reflecting haptic device as a virtual interface. The results presented in this paper introduce details for the complete set-up for a realistic virtual clay modeling task with force feedback. The ISU force-reflecting exoskeleton, coupled with a supporting PUMA 560 manipulator and the virtual clay model are integrated with the WorldToolKit (WTK) graphics display, and the results show that the force feedback from the realistic physically-based virtual environment can greatly enhance the sense of immersion.

Time delayed teleoperation system control, A passivity-based method

A control scheme for teleoperation systems with time delay is proposed based on a passivity concept. This control method requires neither the knowledge of the manipulator systems nor the environmental models. Moreover, the approach is applicable for any time delays. This model independence and time delay independence features make the proposed control method well suitable for teleoperation in the physical world. The applications include remote site explorations, telesurgery, space explorations and teleoperation through the Internet. The main contribution of this method is that it is less conservative than the traditional passivity based method. In our method, the passivity controller only operates when the system loses passivity, while in a traditional passivity formulation, the controller works all the time during the operations that may adversely affect the performance of the system

Applications of neural networks for coordinate transformations in robotics

The use of artificial neural networks is investigated for application to trajectory control problems in robotics. The relative merits of position versus velocity control is considered and a control scheme is proposed in which neural networks are used as static maps (trained off-line) to compute the inverse of the manipulator Jacobian matrix. A proof of the stability of this approach is offered, assuming bounded errors in the static map. A representative two-link robot is investigated using an artificial neural network which has been trained to compute the components of the inverse of the Jacobian matrix. The controller is implemented in the laboratory and its performance compared to a similar controller with the analytical inverse Jacobian matrix.

Multi-tiered control for undergraduate mechatronics

As mechatronics has gained popularity, the use of more sophisticated control in the design of computer controlled systems has also increased. It is reasonable to teach mechatronics using a gradually increasing complexity in control approach, beginning with discrete and combinational logic and progressing to error feedback control. This work presents an overview of the controls taught in the mechatronics course at Iowa State University and focuses on the introduction of control concepts appropriate for undergraduate mechanical engineers.

Virtual cooperating manipulators as a virtual reality haptic interface

One central element in the focus on research into human-machine interfaces is the capability to interact physically with the computer model. The sense of touch and feel is vital for realistic manipulation and control of virtual objects. The research described here is the development and implementation of a new dynamic control strategy using a standard six-degree-of-freedom robot manipulator as a force interface to virtual reality systems. The haptic element of VR interfacing is currently the subject of abundant research, some addressing the stability and control of interactive systems but with much of the focus on the development of new hardware systems to support stable interaction between humans and VR graphics displays. However, general six-degree-of-freedom manipulators are well understood today and are known to have the capability for generating the general force and motion constraints necessary for the design interaction described in the story. This approach to haptic feedback capability is based on the concept of describing a virtual manipulator model that mimics the motion constraints imposed by a virtual surface. This virtual manipulator is conceptually linked to an actual manipulator to form a closed kinematic chain system. The closed chain system equations are used to define a set of constraints that control the actual robot manipulator so as to allow motion only in the free directions of the virtual manipulator. These free directions are also the free motion directions allowed by the virtual surfaces one tremendous advantage of the approach is that the control algorithm is formulated using local error feedback schemes at the robot level providing effective, stable, and simple control of the robotic hardware. Using the proposed control scheme will allow any six-degree-of-freedom manipulator to be used as a haptic interface device.

Haptic Interactions Using Virtual Manipulator Coupling With Applications to Underactuated Systems

Haptic interactions have become increasingly important as an interface to computer-generated simulations in virtual-reality (VR) applications. Many haptic devices are designed to be used as a force feedback mouse, where the users hand is in contact with the haptic device while the object contact and force generation occur on a computer screen. In this paper, we present an approach using a “virtual probe” to interact with the environment and introduce a new method to generate impedance-based haptic forces based on the use of a virtual manipulator. The virtual probe is connected directly to the haptic device and is projected from the hand to the environment, much like a scalpel or sword. As the probe comes in contact with the environment, the haptic device generates appropriate forces on the hand. We extend this approach to include underactuated haptic devices, which do not have fully powered joints. We show that the approach compensates for missing joint actuation in the underactuated haptic devices. We show experimental results for a simple case of haptic interaction; we also present an experimental implementation in six degrees of freedom (DOF) using one of the most popular devices: the PHANTOM.

Contact sensation in the synthetic environment using the ISU force reflecting exoskeleton

Force feedback from the virtual world can greatly enhance the sense of immersion even for simple applications. The ISU force reflecting exoskeleton enables the user to interact dynamically with simulated environments by providing an electromagnetic haptic interface between the human and the environment. The paper describes the high bandwidth electromagnetic haptic interface and how it has been used to provide the sense of contact in the synthetic environment. The air gap between the magnetics, carried by the robot, and the coils attached to the humans digits, allows for small relative motion between the human and the robot without affecting the transmission of forces. This flexibility allows the robot to track the human as well as develop appropriate forces from the virtual world. Three different typical synthetic environments are programmed and tested using the ISU force reflecting exoskeleton haptic interface device. The experimental results shows that the magnetic interface gives adequate force levels for perception of virtual objects, enhancing the feeling of immersion in the virtual environment.

Experimental Results for Force Distribution in Cooperating Manipulator Systems Using Local Joint Control

Local control schemes using only position and rate errors to generate control forces are widely used for control of open- chain, serial-link robotic mechanisms, When two or more such open chains interact, closed kinematic chain, redundantly actu ated mechanisms are formed. Recent work has shown that the vector of joint forces produced using a local proportional-plus- derivative feedback scheme for the control of a cooperating manipulator system results in a vector of joint torques with a minimum weighted Euclidean norm. The current work presents the derivation of this force distribution and experimental evi dence to corroborate the analytic results. The data presented are obtained from an experimental cooperating manipulator system developed specifically for use in the application of theo retical control approaches in cooperating hardware systems.