Pietro Buttolo

Pen-based force display for precision manipulation in virtual environments

We describe the structure of a force display recently implemented for precision manipulation of scaled or virtual environments. We discuss the advantages of direct-drive parallel manipulators over geared serial manipulators for human-robot interaction application and introduce the serial-parallel structure we chose for our robot which interfaces with the human operator either at the fingertip or at the tip of a freely held pen-like instrument. We derive the statics and the dynamics, and then introduce the optimization criteria that allowed us to choose the dimensional parameters for the force display. Finally we show some of the potential application for this device.

Architectures for shared haptic virtual environments

Abstract The lack of force feedback in visual-only simulations may seriously hamper user proprioception, effectiveness and sense of immersion while manipulating virtual environments. Haptic rendering, the process of feeding back force to the user in response to interaction with the environment is sensitive to delay and can become unstable. In this paper we will describe various techniques to integrate force feedback in shared virtual simulations, dealing with significant and unpredictable delays. Three different implementations are investigated: static, collaborative and cooperative haptic virtual environments.

Manipulation in real, virtual and remote environments

In this paper we describe a novel experimental procedure for the evaluation of a telemanipulator performance. A group of subjects performed the same set of tasks directly on a physical setup, on a virtual implementation capable of providing visual and force feedback through an haptic display, and remotely on the real setup using a telemanipulation system. Using this experimental procedure we were able to decouple the effects on the overall telemanipulator performance introduced by the single components of the system, master manipulator, display, slave manipulator rind bilateral controller.

Sliding control of force reflecting teleoperation: Preliminary studies

In this paper, sliding mode nonlinear control is applied to force reflecting teleoperation. Various forms of the sliding mode control law are derived for force feedback master manipulation with an arbitrary factor for force and position scaling. Experiments were performed on a one axis test system and frequency domain Hybrid 2-port matrices are measured and compared between the sliding mode controller and a classical position error-based feedback controller. Time domain experiments are also performed. The model-based portion of the sliding mode controller was shown to be responsible for most of its performance improvement, but the nonlinear sliding component was essential for steady-state position accuracy and robust stability.

Scaling of direct drive robot arms

This article studies the ways that the performance of direct drive (DD) serial robots changes as system size is changed. We are particularly interested in the physical laws for scaling down direct drive arms to small sizes. Using theoretical scaling analysis, we show that there is a net physical performance advantage to small direct drive arms. A key factor for direct drive robot performance is the torque-to-mass ratio of the actuators, U. We show how U varies with the scale of DD actuators, and we also calculate how the dynamic performance varies with scale and U. We compare our calculations with experimental measurements of actuators of various sizes taken from small hard disk drives and compare them with published data for larger motors. Finally, we describe a prototype, five- axis, direct drive serial arm having a reach of 10 cm and a work volume of about 136 cm3. Some potential applications are briefly discussed.

A haptic hybrid controller for virtual prototyping of vehicle mechanisms

In this paper the Haptic Buck, a system to interactively design and evaluate vehicle mechanisms, is presented as an alternative to physical prototyping. At the core of the package are a 3D GUI interface to quickly and intuitively design and modify mechanisms and a novel haptic control scheme to achieve high-quality rendering of very large mechanisms, such as full scale modeling of vehicle liftgate, doors, and seat assemblies.

Manual Detection of Spatial and Temporal Torque Variation through a Rotary Switch

We report three experiments on manual detection of torque variations experienced through a rotary switch. The experiments were designed to investigate whether torque perception was determined by the spatial or by the temporal characteristics of the rotary switch. In Exp. I, manual detection thresholds of torque variation were measured with raised sinusoidal torque profiles that varied in spatial period from 2.8deg to 180deg per cycle. In Exp. II, the same was measured for torque profiles that varied in temporal frequency from 2 to 300 Hz. Exp. III was similar to Exp. 1 except that the participants were required to turn the rotary switch at two different speeds for each of seven spatially specified torque profiles (spatial period: 2.8deg to 90deg per cycle). A comparison of the thresholds obtained in Exp. III and those in Exps. I and II suggests that the detection of torque variations depends on the spatial, not temporal, specification of the torque profiles. Our results can potentially shed new light on the design and engineering specification of rotary switches.

Design and performance of a high fidelity, low mass, linear haptic display

We built a high fidelity, low mass, linear haptic display, with a peak force output of 8.5 Newtons, continuous force output of 1.3 Newtons, range of motion of approximately 15 millimeters, sensing resolution of 0.5 microns, and a -3 dB bandwidth of approximately 550 Hz. By having low apparent mass of approximately 5 grams, we can realistically render linear switches, which themselves have a moving mass of only a few grams. This device utilizes a low inertia rotary motor, but over only a limited range of motion, allowing it to be driven without commutation. We constructed a linear, current controlled amplifier to drive the system. Additionally, the motor windings allow us to use electrical damping to add physical damping to the system to improve its performance.

Multi-finger Haptic Displays for Characterization of Hand Response

This chapter will describe some properties of multi-finger haptic interaction and two devices which support it. Multi-finger haptic interaction can involve many contacts with the environment, but can also involve only one contact point when mediated by a tool such as a pen. As multiple fingers interact with the environment, their individual biomechanics and their sensory properties interact to form the net mechano-sensory properties of the interaction. This chapter will look at such interactions in two particular cases, spatially varying stiffness of the pen grasp, and sensory thresholds of multi-finger versus single finger interaction with haptic features. To characterize the stiffness of the pen-like grasp in various directions, we describe experiments in which force steps (randomized in amplitude and direction) were applied to subjects’ pen-like tools in the plane tangential to the tip. From these, the stiffness ellipse could be identified. A dynamical model of the fingers positioned similarly to the user’s grasp was used to predict the stiffness ellipsoids with similar results. The ellipsoids were shown to be a function of the squeezing force with which the subjects performed the grasps. Much of the research on sensitivity and sensory thresholds is based on measurements with a single finger. We developed a multi-finger haptic device (MFHD) to allow two high quality degrees of freedom for each of four fingers in a natural pose. With this device we could compare the sensory thresholds between single finger and multiple finger haptic exploration.

Determine Mesh Orientation by Voxel-Based Principal Component Analysis

In this paper we propose a new method to determine the part orientation of a 3D mesh based on Principal Component Analysis (PCA). Although the idea and practice of using PCA to determine part orientation is not new, it is not without practical issues. A major drawback of PCA, when it comes to dealing with meshes comprised of nodes and elements, is that the results are tessellation-dependent because of its sensitivity to variability. Two CAE meshes derived from the same CAD model but with different mesh node distribution characteristics, for instance, can yield different principal components. This is an undesirable outcome because the primary concern in model reorientation is shape, not the representational details of the shape. In order to reduce the influence of node characteristics, weight factors were proposed in the past, but the improvement is limited. To overcome this limitation, we must eliminate the influence of mesh node distribution. We achieve this by introducing an intermediate workspace, which is subsequently voxelized. We then find the intersection of the mesh model with the voxelized workspace. We collect the intersecting voxels to form an intermediate, tessellation-independent representation of the mesh. Applying PCA to this “neutralized” representation allows us to achieve mesh-property-independent results. The voxel representation also provides an opportunity of computational efficiency. We implemented an octree data structure to store the voxels and implemented a fast intersection (between a mesh element and a voxel) check procedure utilizing the interval overlap check derived from the separating axis theorem. Practical issues concerning determination of the voxel space resolution is addressed. A two-step trial and correction approach is proposed to enhance the consistency of results. Our voxel-based PCA is robust, fast, and straightforward to implement. Application examples are shown demonstrating the effectiveness and efficiency of this approach.Copyright