Robot control algorithms often rely on measurements of robot joint velocities, which can be estimated by measuring the time between encoder edges. When encoder edges occur infrequently, such as at low velocities and/or with low resolution encoders, this measurement delay may affect the stability of closed-loop control. This is evident in both the joint position control and Cartesian impedance control of the da Vinci Research Kit (dVRK), which contains several low-resolution encoders. We present a hardware-based method that gives more frequent velocity updates and is not affected by common encoder imperfections such as non-uniform duty cycles and quadrature phase error. The proposed method measures the time between consecutive edges of the same type but, unlike prior methods, is implemented for the rising and falling edges of both channels. Additionally, it estimates acceleration to enable software compensation of the measurement delay. The method is shown to improve Cartesian impedance control of the dVRK.

Ground-based teleoperation of robots in space is subject to time delays of several seconds or more. This leads to the use of model-based approaches, where the operator interacts with a model (simulation) of the remote environment and the remote robot attempts to reproduce the results of that interaction. But, it is also desirable for the operator to view (delayed) images from the remote scene. These images, however, are often from one or more monocular cameras mounted on the robot end-effector, which leads to several other problems: unintuitive teleoperation due to the eye-in-hand configuration, limited field of view, and lack of stereo visualization. We present an augmented virtuality interface for teleoperation, which can solve these problems by projecting the real camera images onto a registered 3D model of the environment and allowing the operator to select any desired viewpoint. This approach is suitable when there is at least a partial model of the environment, as is the case for satellite servicing. The proposed method begins with a video survey to register the 3D model to the physical environment, followed by a user interface that presents a stereo visualization of the model, augmented by projections of real camera images onto the model. We quantitatively and qualitatively compare the augmented virtuality images to real camera images taken from the same viewpoint and perform experiments to evaluate the efficacy of the augmented virtuality paradigm for teleoperation. The results suggest that this approach can improve operator situation awareness, potentially leading to better performance, especially when the camera views are unintuitive or limited.

Suturing is a challenging and highly dexterous task in minimally invasive surgery, even with the assistance of robotic surgical systems. In this work, we propose a simple yet versatile impedance virtual fixture framework, which can be applied on the master manipulator in a tele-operated robotic surgical system. With this framework, we further develop two types of virtual fixtures that assist with the needle passing and knot tying sub-tasks in suturing. The paper also presents the results of a 14-participant user study for both needle passing and knot tying sub-tasks, showing that virtual fixture assistance for novice users increases the needle passing exit point accuracy, reduces the number of errors (suture slip) in knot tying, and simultaneously decreases the task completion time and overall operator workload.

In this paper, a real-time control network based on Ethernet and FireWire is presented, where Ethernet provides a convenient, cross-platform interface between a central control PC and a FireWire subnetwork that contains multiple distributed nodes (I/O boards). Real-time performance is achieved because this architecture limits the number of Ethernet transactions on the host PC, benefits from the availability of real-time Ethernet drivers, and uses the broadcast and peer-to-peer capabilities of FireWire to efficiently transfer data among the distributed nodes. This approach and resulting benefits are comparable to EtherCAT, but preserves existing investments in FireWire-based controllers and relies only on conventional, vendor-neutral network hardware and protocols. The system performance is demonstrated on the da Vinci Research Kit (dVRK), which consists of 8 FireWire nodes that control 2 Master Tool Manipulators (MTMs) and 2 Patient Side Manipulators (PSMs), for a total of 28 axes. This approach is generally applicable to interface existing FireWire-based systems to new control PCs via Ethernet or to serve as an open-source alternative to EtherCAT for new designs.

Direct teleoperation with multisecond time-delayed telemetry between master and slave is challenging for humans to perform. When controlling a holonomic robot with many degrees of freedom, operators may incidentally provide commands in an intended direction without realizing their mistake until receiving feedback several seconds later. For some applications, imposing a virtual nonholonomic constraint (VNHC) on the motion of the end effector can help prevent operators from moving in an unintended direction by reducing the number of controllable degrees of freedom. This paper presents the development of a VNHC for a planar time-delayed telerobotic task, motivated by an on-orbit telerobotic satellite servicing operation. We also describe a nonholonomic virtual fixture (NHVF) that adheres to the VNHC to further reduce the potential for operators to input mistaken commands. We report the results of a pilot study in which teleoperation with a VNHC was found to have comparable task performance to holonomic planar teleoperation, while decreasing operator workload. The NHVF was found to decrease performance slightly, though user feedback indicated that a differently implemented virtual fixture and controller may improve performance.

We present a telerobotics research platform that provides complete access to all levels of control via open-source electronics and software. The electronics employs an FPGA to enable a centralized computation and distributed I/O architecture in which all control computations are implemented in a familiar development environment (Linux PC) and low-latency I/O is performed over an IEEE-1394a (FireWire) bus at speeds up to 400 Mbits/sec. The mechanical components are obtained from retired first-generation da Vinci ® Surgical Systems. This system is currently installed at 11 research institutions, with additional installations underway, thereby creating a research community around a common open-source hardware and software platform.

Cooperatively controlled robots are used in many kinds of applications, including surgical robot applications where the surgeon can guide the robot end effector to a desired position. Often, a 6 degree-of-freedom (DOF) force/torque sensor is installed. However, in some cases, the sensor is only used to impose safety thresholds and to support the robot guidance task. In cases where high guidance accuracy is not required, it can be difficult to justify the added cost of a 6 DOF force sensor. One lower-cost solution is to incorporate a joystick or similar input device, but this requires additional hardware and removes the surgeon's hands from direct interaction with the robot end-effector. This paper presents a method for achieving cooperative force control without a force sensor. The method utilizes motor current feedback and uses a calibrated current value for force estimation. The novelty of this method is that it can be applied to non-backdrivable robots. It is implemented on a 2-DOF XY stage and experiments are conducted to demonstrate accuracy and performance on this non-backdrivable robot.