Evaluation of Delay of a Teleultrasound Robotic System for Musculoskeletal Imaging

Abstract

Teleoperated systems are used in multiple fields since they allow the user to remotely work in locations where it would otherwise be infeasible due to cost, safety, or accessibility. However, due to the vast distances involved, teleoperated systems suffer from degraded communication between the operator and end device. This often takes the form of either delay or loss in the control signal. Understanding this degradation is necessary to advance the development of teleoperated systems. The objective of this research is to identify how normal operation of a teleoperated device is altered by delay in the communication signal and how system performance can be improved. A 4-degrees-of-freedom (4-DOF) teleultrasound robot was used to measure the time delay between a command and its response as well as the position error resulting from the time delay. The delay was measured by both a video recording and a network analysis software. The position error was measured by comparing physical coordinates of the actual robot with position of a simulated robot. These tests were then moved from a Wireless Local Area Network (WLAN) to a Virtual Local Area Network (VLAN) to see if there is a noticeable change from the different network topology. This study verified that the communication channel between the operator and robot is a significant source of delay. In the experimental WLAN setup, the system experienced an average of about 300 milliseconds of delay. It was verified that signal degradation affects operation of the system. The error in displacement was found to have a quadratic relation with signal delay. It was found that a VLAN network performed better than a WLAN network, with about 40% reduction in average delay time and 70% reduction in maximum displacement error. Contribution of this work was on quantifying effects of delay in position of a 4-DOF end-effector in a teleultrasound robot.

MSK-TIM: A Telerobotic Ultrasound System for Assessing the Musculoskeletal System

“…The mean and median delay were 249 and 250 ms. These values are consistent with previous measurements which found the mean delay to be 239 ms [26]. Note that the measured maximum for the system delay is smaller than the maximum network delay.…”

“…and lack of easy remote connectivity between slave and master stations [4,26]. Therefore this paper describes research conducted to (1) investigate how adding visual force feed back affects patients' comfort and experience, (2) study how using a wireless connectio changes the delay time and quality of control, and (3) explore how introducing remot control of ultrasound functions can help optimize image quality.…”

“…Therefore, the two stations can be physically separated to two locations with internet access. To investigate how this change affects system latency, this study investigates both the VPN and the Wireless Local Area Network (WLAN) employed in previous studies [4,26]. An explanatory diagram can be seen in Figure 4.…”

“…Therefore, an informed choice of delay is beneficial in controller design. Previous work has measured a full system delay within a local network [26]. This study will investigate both the system and network delay in remote control over the internet.…”

“…A predecessor to this system has been tested and shown to be feasibly used over a Wireless Local Area Network (WLAN) but had room for improvement. Previous trials to develop a musculoskeletal telerobotic machine had a few limitations such as lack of remote control of ultrasound functions, lack of force feedback, and lack of easy remote connectivity between slave and master stations [4,26]. Therefore, this paper describes research conducted to (1) investigate how adding visual force feedback affects patients' comfort and experience, (2) study how using a wireless connection changes the delay time and quality of control, and (3) explore how introducing remote control of ultrasound functions can help optimize image quality.…”