This paper presents the theoretical analysis and the experimental validation of the force sensing capabilities of continuum robots. These robots employ superelastic NiTi backbones and actuation redundancy. The paper uses screw theory to analyze the limitations and provide geometric interpretation to the sensible wrenches. The analysis is based on the singular value decomposition of the Jacobian mapping between the configuration space and the twist space of the end effector. The results show that the sensible wrenches belong to a 2-D screw system and the insensible wrenches belong to a 4-D screw system. The theory presented in this paper is validated through simulations and experiments. It is shown that the force sensing errors have an average of 0.34 g with a standard deviation of 0.83 g. Another experiment of generating the stiffness map of a silicone strip suggests possible medical application of palpation for tumor detection. The presented study allows force sensing in challenging environments where placing force sensors at the distal end of a robot is not possible due to limitations such as size and MRI compatibility.

An Investigation of the Intrinsic Force Sensing Capabilities of Continuum Robots

This paper reports some recent analysis and modeling results obtained while developing a tele-robotic system for minimally invasive surgery of the throat. One of the main enabling components of this system is a Distal Dexterity Unit that implements a novel design using a flexible multi-backbone snake-like unit with actuation redundancy and push-pull actuation. The design of this snake-like unit is compared to other alternative designs that use a single flexible-backbone and wire-actuation. A unified kinematic and virtual work model is used to perform this comparison between a multi-backbone snake like unit with an equal-diameter snake-like unit using a single flexible backbone and wire actuation. The comparison is presented for several actuation redundancy resolutions that minimize the load on the flexible backbones. The results show that the multi-backbone design is superior to the alternative wire-actuated designs using a single flexible backbone. The advantages manifest in smaller required actuation forces on the backbones and, as a result, a reduced risk of buckling of the backbones and enhanced potential downsize scalability.

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Snake-Like Units Using Flexible Backbones and Actuation Redundancy for Enhanced Miniaturization

The reduced access conditions of minimally invasive surgery and therapy (MIST) impair or completely eliminate the feel of tool—tissue interaction forces. Many researchers have been working actively on the development of force sensors and sensing techniques to address this problem. The goal of this survey article is to summarize the state of the art in force sensing techniques for medical interventions in order to identify existing limitations and future directions. A literature search was performed from January to July 2009 using a combination of keywords relevant to the area, including force, sensor, sensing, haptics, and minimally invasive surgery.The literature search resulted in 126 articles with valuable content. This article presents a summary of the force sensing technologies, design specifications for force sensors in clinical applications, force sensors and sensing instruments that have been developed for MIST, and the experiments performed to determine the need for force information. Ope...

Force sensing and its application in minimally invasive surgery and therapy: A survey

This paper presents the intrinsic capability of full-wrench estimation of multisegment continuum robots with multiple flexible backbones. Intrinsic-full-wrench estimation refers to the ability of continuum robots to also serve as force and moment sensors by using measurements of axial loads on their backbones. This end-effector-as-sensor approach fulfills the rapidly increasing needs for miniature-robotic-surgical tools with haptic sensing ability subject to various limitations, such as size, magnetic resonance imaging (MRI) compatibility, sterilizability, etc. A performance index for the intrinsic wrench-sensing capability is introduced and evaluated to show how this index can serve as a design guide for continuum robots that provide force sensing.

Intrinsic Wrench Estimation and Its Performance Index for Multisegment Continuum Robots

The 10 mm incisions used in minimally invasive cancer surgery prevent the direct palpation of internal organs, making intraoperative tumor localization difficult. A tactile sensing instrument (TSI), which uses a commercially available sensor to measure distributed pressure profiles along the contacting surface, has been developed to facilitate remote tissue palpation. The objective of this research is to assess the feasibility of using the TSI under robotic control to reliably locate underlying tumors while reducing collateral tissue trauma. The performance of humans and a robot using the TSI to locate tumor phantoms embedded into ex vivo bovine livers is compared. An augmented hybrid impedance control scheme has been implemented on a Mitsubishi PA10-7C to perform the force/position control used in the trials. The results show that using the TSI under robotic control realizes an average 35% decrease in the maximum forces applied and a 50% increase in tumor detection accuracy when compared to manual manipulation of the same instrument. This demonstrates that the detection of tumors using tactile sensing is highly dependent on how consistently the forces on the tactile sensing area are applied, and that robotic assistance can be of great benefit when trying to localize tumors in minimally invasive surgery.

Robot-assisted Tactile Sensing for Minimally Invasive Tumor Localization

Background
At present, the da Vinci® surgical robot system does not provide haptic feedback. One of the authors has proposed a contact-force sensing method called the ‘overcoat method’, in which the instrument/driver is supported by force sensors. In the da Vinci robot, the instrument jaws are powered by a wire-pulley mechanism; thus, in order to apply the overcoat method to the da Vinci system, we must transfer the power through a frame that is supported by force sensors.

Methods
The authors have attempted to add a force-sensor function to the Sterile Adapter® of the da Vinci system. In developing a sensorized adapter, a new configuration of force sensors and a new axial-force-free (AFF) joint have been devised in order to obtain an independent ‘axial force effect’ from the drive torque fed from the da Vinci robot arm.

Results
The force-sensing errors of the present system have been measured to have a maximum value of approximately 0.2 N while driving the jaws, and a maximum value of approximately 0.2 N when the robot arm is inclined with some excitation. Some impact reference forces applied on to the ends of the jaws agree with the outputs of the sensorized adapter to within <0.05 N.

Discussions
It is shown that the new adapter can be sterilized. One apprehension is that the total weight of the new adapter—approximately 1.2 kg—might unbalance the robot arm. In the case of the new adapter, the centre-line of the instrument shaft is shifted externally through approximately 3.5 mm from its original position. However, a new cannula for the da Vinci robot might solve this problem.

Conclusion
The new configuration of force sensors and the new AFF joint work well in their basic functions. The total force-sensing error is estimated as approximately 0.5 N. One of the main reasons for the error appears to be the deformation of the adapter frame. Copyright © 2008 John Wiley & Sons, Ltd.

Adapter for contact force sensing of the da Vinci robot.

For fine surgical operation by slave robot, master robot needs the information of the contact force loaded on the tip of the surgical instrument. One of major problems in sensing the force is frictional disturbance between the trocar and the instrument. One of authors proposed a new method named overcoat method where the whole instrument is supported by force sensors. This paper tried to construct a force measuring system with the basic type of the overcoat method. It discussed about the compensations of gravity and acceleration force of the instrument in relations to the pose and motion of the instrument. The tried system measured the tip-loaded force in sensitivity about 0.05 N.

New sensing method of force acting on instrument for laparoscopic robot surgery

For fine surgical operation by slave robot, master robot needs the information of the contact force loaded on the tip of the surgical instrument. One of major problems in sensing the force is frictional disturbance between the trocar and the instrument. One of authors proposed a new method named overcoat method where the whole instrument is supported by force sensors. This paper tried to construct a force measuring system with the trocar type of the overcoat method. It discussed about the compensations of gravity and acceleration force of the instrument in relation to the pose and motion of the instrument. The tried system measured the tip-loaded force in absolute accuracy about 0.3 N and in sensitivity about 0.05 N.

Measurement of force acting on surgical instrument for force-feedback to master robot console

For delicate operations conducted using surgical robot systems, surgeons need to receive information regarding the contact forces on the tips of surgical instruments. For the detection of this contact force, one of the authors previously proposed a new method, called the overcoat method, in which the instrument is supported by sensors positioned on the overcoat pipe. This method requires cancellation of the acceleration forces of the instrument/holder attached to the overcoat sensor. In the present report, the authors attempt to use acceleration sensors to obtain the acceleration forces of the instrument/holder. The new cancellation method provides a force-detection accuracy of approximately 0.05-0.1 N for a dynamic response range of up to approximately 20 Hz, compared to approximately 1 Hz, which was achieved by using acceleration forces based on the theoretical robot motion.

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Contact force measurement of instruments for force-feedback on a surgical robot: acceleration force cancellations based on acceleration sensor readings

From a number of fish heads W of the same kind of fish and of roughly the same shape, pituitaries M as useful portions in the fish heads W are collected. A useful portion line is preliminarily determined which passes pituitaries M as useful portions of the number of fish heads W having different sizes when the fish heads W are rested in a specific posture, and each of fish heads W to be processed is rested in the specific posture, and the rested fish head W is cut in the vicinity of the preliminarily determined useful portion line substantially along the useful portion line to expose an useful portion, and a brain as an untargeted portion which is present in a cut surface F is removed to expose the pituitary M, and the exposed pituitary M is collected.

Shigeyuki Shimachi

Papers

Adapter for contact force sensing of the da Vinci robot.

New sensing method of force acting on instrument for laparoscopic robot surgery

Measurement of force acting on surgical instrument for force-feedback to master robot console

Contact force measurement of instruments for force-feedback on a surgical robot: acceleration force cancellations based on acceleration sensor readings

Method for collecting useful portions of fish heads and device for collecting useful portions of fish head