Force Reflecting Endoscopic Grasper

Abstract

The Force Feedback endoscopic Grasper - FREG incorporates teleoperation technology into an existing, reusable, endoscopic grasper for minimally invasive surgery. The FREG system includes two subsystems. The master and the slave each consist of an actuator and a position encoder. The tool tip, pull/push rod and tube is mounted on the slave subsystem which is inserted into the patient's body through an access port. The proximal end of the instrument tube is clamped to a supporting post of the slave. The pull/push rod operating the tool tip (jaws) is linked to the electromagnetic actuator via a ball and socket joint. The two finger loops (user interface) of the grasper are mounted on the master subsystem. The distal finger loop is connected to an actuator/encoder pair identical to those on the tool shaft enabling the surgeon to control the tool tip.

To increase sensing resolution, the encoder wheels are connected to the actuation axes via pulleys and a kevlar drive belt having a multiplication ratio of 1:3.6. As a consequence, both master and slave position sensors have 1400 quadrature position counts over the full 0.6 radian (34.4 Deg) motion range. The FREG actuators are flat coil actuators modified from hard disk drive head positioning actuators. Hard disk drive head actuators have many advantages for precision robotics and force feedback devices. Actuators taken directly from 5.25 inch (133mm) hard drives with a maximum torque of 0.1NM at 2.0 A (based on steady state coil temperature of 93o C) did not produce convincing subjective grasping sensations. The actuator magnets were replaced with custom made Nd-Fe-B magnets having approximately triple the energy product of the Al-Ni-Co magnets used in the disk drive actuator. The coil and bearing assembly was retained. To realize the full flux increase from the new magnets, new frames were built from high permeability iron to prevent backing iron saturation. The new actuator magnets and frames increased the torque output to 0.3 NM, but preserved the desirable qualities of low torque ripple, low friction, and low back-driving inertia.

The Laparoscopic instrument used in these experiments is a stainless steel Babcock grasper (Carl Storz Inc., model # 30420 BL) with a square jaw grasping surface area measuring 9.4 x 8.5 mm. The tool shaft is 5 mm in diameter and 38 cm long from the proximal attachment to the instrument tip. The shaft and mount allow 360 degree rotation of the tool about its long axis. This system allows easy change of shaft length, diameter, and tool tip conformations. Laparoscopic tools compatible with the mounting system are readily available from various manufacturers.

The control system supports two modes of operation (i) bi-lateral force feedback - teleoperation, and (ii) programmed automatic grasping (palpation) operation for tissue characterization. Proportional-derivative (PD) controllers were designed for both the master and slave using a linear dynamic model of the device and conventional control techniques. The force feedback controller is based on the well known bi-lateral, position error based, teleoperation system. In this design, the measured position of each side serves as the reference position input for the other.

Biomechanical Characteristics of Internal Organs' Soft Tissues - In-Vivo measurements in minimally Invasive Surgery - Phase 1

FREG - Overview of the FREG in a surgical setting
56K Modem (128K) | T1 Connection (516K)

FREG - Automatic Palpation of Internal Organ (Soft Tissue)
56K Modem (235K) | T1 Connection (1M)

(*) Note: Most of the BRL publications are available on-line in a PDF format. You may used the publication's reference number as a link to the individual manuscript.

[111]
B. Hannaford, J. Trujillo, M. Sinanan, M. Moreyra, J. Rosen, J. Brown, R. Lueschke, M. MacFarlane, 'Computerized Endoscopic Surgical Grasper,' Proceedings, MMVR-98 (Medicine Meets Virtual Reality), San Diego, January 1998.

[121]
M. MacFarlane, J. Rosen, B. Hannaford, C. Pellegrini, M. Sinanan, 'Force Feedback Grasper Helps Restore the Sense of Touch in Minimally Invasive Surgery.,' Journal of Gastrointestinal Surgery, vol. 3, pp. 278-285, 1999.

[122]
J. Rosen, B. Hannaford, M. MacFarlane, M. Sinanan, 'Force Controlled and Teleoperated Endoscopic Grasper for Minimally Invasive Surgery - Experimental Performance Evaluation,' IEEE Transactions on Biomedical Engineering, vol. 46, pp. 1212-1221, October 1999.