Teeranoot Chanthasopeephan

Measuring Forces in Liver Cutting: New Equipment and Experimental Results

AbstractWe are interested in modeling the liver cutting process as accurately as possible by determining the mechanical properties experimentally and developing a predictive model that is self-consistent with the experimentally determined properties. In this paper, we present the newly developed hardware and software to characterize the mechanical response of pig liver during (ex vivo) cutting. We describe the custom-made cutting apparatus, the data acquisition system, and the characteristics of the cutting force versus displacement plot. The force-displacement behavior appears to reveal that the cutting process consists of a sequence of intermittent localized crack extension in the tissue on the macroscopic scale. The macroscopic cutting force-displacement curve shows repeating self-similar units of localized linear loading followed by sudden unloading. The sudden unloading coincides with observed onset of localized crack growth. This experimental data were used to determine the self-consistent local effective Youngs modulus for the specimens, to be used in finite element models. Results from finite element analyses models reveal that the magnitude of the self-consistent local effective Youngs modulus determined by plane-stress and plane-strain varies within close bounds. Finally, we have also observed that the local effective Youngs modulus determined by plane stress and plane strain analysis decreases with increasing cutting speed.

Modeling Soft-Tissue Deformation Prior to Cutting for Surgical Simulation: Finite Element Analysis and Study of Cutting Parameters

This paper presents an experimental study to understand the localized soft-tissue deformation phase immediately preceding crack growth as observed during the cutting of soft tissue. Such understanding serves as a building block to enable realistic haptic display in simulation of soft tissue cutting for surgical training. Experiments were conducted for soft tissue cutting with a scalpel blade while monitoring the cutting forces and blade displacement for various cutting speeds and cutting angles. The measured force-displacement curves in all the experiments of scalpel cutting of pig liver sample having a natural bulge in thickness exhibited a characteristic pattern: repeating units formed by a segment of linear loading (deformation) followed by a segment of sudden unloading (localized crack extension in the tissue). During the deformation phase immediately preceding crack extension in the tissue, the deformation resistance of the soft tissue was characterized with the local effective modulus (LEM). By iteratively solving an inverse problem formulated with the experimental data and finite element models, this measure of effective deformation resistance was determined. Then computational experiments of model order reduction were conducted to seek the most computationally efficient model that still retained fidelity. Starting with a 3-D finite element model of the liver specimen, three levels of model order reduction were carried out with computational effort in the ratio of 1.000:0.103:0.038. We also conducted parametric studies to understand the effect of cutting speed and cutting angle on LEM. Results showed that for a given cutting speed, the deformation resistance decreased as the cutting angle was varied from 90deg to 45deg. For a given cutting angle, the deformation resistance decreased with increase in cutting speed

Measuring grasping and cutting forces for reality-based haptic modeling

Abstract The modeling of grasping and cutting in surgery are two fundamental tasks that must be achieved for the development of a reality-based haptic interface in robot-assisted surgery. Currently, the lack of these models with soft tissue has limited the accuracy of such interfaces in surgery. As a result, we have taken the first steps in realizing soft tissue models through the development of an automated laparoscopic grasper and tissue cutting equipment to characterize grasping and cutting tasks in minimally invasive surgery (MIS). The grasper is capable of generating force feedback that can be felt through a haptic interface device thereby allowing a user to feel the stiffness of the tissue that is being grasped. The cutting equipment employs a surgical scalpel attached to a six-axis force/torque sensor to measure the forces during cutting. The scalpel follows a linear motion created by a DC motor and leadscrew assembly.

Measuring forces in liver cutting for reality-based haptic display

Reality-based modeling of deformable tissues is critical for providing accurate haptic feedback to the surgeon in common surgical tasks such as grasping and cutting organs/tissues. In reality-based modeling, we are interested in modeling tissues as accurately as possible by determining the mechanical properties experimentally and developing a predictive model that is self consistent with the experimentally-determined properties. In this paper, we present the newly developed hardware and software to characterize the mechanical response of pig liver during (ex-vivo) cutting. The macroscopic cutting force-displacement curve shows repeating self-similar units of localized linear loading followed by sudden unloading. The sudden unloading coincides with onset of localized crack growth. This experimental data was used to determine the self-consistent local effective Youngs modulus of the specimens to be used in finite element models. Results from plane-stress and plane-strain finite element analyses reveal that the magnitude of the self-consistent local effective Youngs modulus varies within close bounds.

Determining Fracture Characteristics in Scalpel Cutting of Soft Tissue

This paper addresses the characteristic response of soft tissue to the growth of a cut (cracking) with a scalpel blade. We present our experimental equipment, experiments, and the results for scalpel cutting of soft tissue. The experimentally measured cut-force versus cut-length data was used to determine the soft tissues resistance to fracture (resistance to crack extension) in scalpel cutting. The resistance to fracture (the toughness) of the soft tissue is quantified by the measure R defined as the amount of mechanical work needed to cause a cut (crack) to extend for a unit length in a soft-tissue sample of unit thickness. The equipment, method, and model are applicable for all soft tissue. We used pig liver as soft-tissue samples for our experiments

Impact reduction mobile robot and the design of the compliant legs

In most mobile robots, the ability to move from point to point in various types of terrain was the most crucial part to the design. Being able to survive through impact conditions is also essential for robots under hazardous circumstances such as rescue robots or military robots. In this paper, we designed and developed a robot with impact reduction mechanism which is based on the compliant design of its legs. The stiffness of the legs was designed to not only to serve walking purposes but also to help reduce the impact while dropping. An experiment was set to investigate how the radius of curvature of the connecting plate and the compliant leg of the robot play a role in impact absorption. The radius of curvature is one of the key factors which vary the stiffness of the compliant parts. With this design, the robot will gradually press the ground during landing using springlike legs. The compliant legs with nonlinear spring constant help absorb impact energy while the robot hits the ground. During drop-landing motion, the robot also transforms itself from a spherical shape into a legged robot while landing. The legs are extended into a walking mechanism on uneven terrain and retracted to create a ball shaped robot for rolling motion over smooth terrain. The transformation between the spherical shaped robot and the legged robot increase its motion capabilities under various conditions including falling, rolling and walking.

Position control of SMA actuator for 3D tactile display

The purpose of this study is to design and fabricate an actuator system for a 3D tactile display. Small size actuator or portable actuator has many possible applications in medicine and industry. In the past, motors have been widely used to create motion in large-area tactile displays. Thus, the device discussed in this paper uses shape memory alloy (SMA) which allows us to create a small, lightweight and high-resolution tactile display. However, there are also challenges using SMA as actuator. The nonlinear hysteresis properties of the SMA cause difficulties during the control of the display. Our design is an 8x8 display consists of 64 SMA springs to create motion for 64 pin display. Each of the pin display takes approximately 0.4 seconds to response to the input. The pin displacement can travel up to 25mm.

Deformation resistance in soft tissue cutting: a parametric study

Characterizing and modeling of soft tissue deformation during cutting is important for developing a reality based haptic interaction model for surgical training and simulation. In this study, soft tissue cutting experiments were performed (ex-vivo) while monitoring the cutting forces and blade displacement for various cutting speeds (ranging from 0.1cm/sec-2.54cm/sec) and cutting angles (for 0/spl deg/ and 45/spl deg/ cutting angle). The measured force-displacement curves in all cases exhibit a characteristic pattern: repeating units formed by a segment of linear loading (deformation of tissue) and immediately followed by a segment of sudden unloading (localized crack extension in the tissue). This paper addresses the characterization of the deformation resistance during the deformation segment. The variation of this deformation resistance with cutting parameters is also determined. The deformation resistance to the cutting blade was quantified via a quantity designed as the local effective modulus (LEM) of the tissue. For a given cutting speed, the deformation resistance decreases as the cutting angle is varied from 0/spl deg/ to 45/spl deg/. For each cutting angle, the deformation resistance decreases with cutting speed. The variation of deformation resistance versus cutting speed is linear at 0/spl deg/ cutting angle and is nonlinear at 45/spl deg/ cutting angle.

Evaluation of Stress Distribution on Implant-Retained Auricular Prostheses:: The Finite Element Method

PURPOSE The purpose of this study was to evaluate stress distribution around two craniofacial implants in an auricular prosthesis according to the removal forces. Three attachment combinations were used to evaluate the stress distribution under removal forces of 45 and 90 degrees. MATERIALS AND METHODS Three attachment designs were examined: (1) a Hader bar with three clips; (2) a Hader bar with one clip and two extracoronal resilient attachments (ERAs); and (3) a Hader bar with one clip and two Locators. The removal force was determined by means of an Instron universal testing machine with a crosshead speed of 10 mm/minute. All three designs were created in three dimensions using SolidWorks. The applied removal force and the models were then introduced to finite element software to analyze the stress distribution. RESULTS The angle of removal force greatly affected the magnitude and direction of stress distribution on the implants. The magnitude of stress under the 45-degree removal force was higher than the stress at 90 degrees. The combination of the 1,000-g retention clip and 2,268-g retention Locator exhibited the highest stress on the implant flange when the removal force was applied at 45 degrees. CONCLUSION The removal angle greatly influences the amount of force and stress on the implants. Prosthodontists are encouraged to inform patients to remove the prosthesis at 90 degrees and, if possible, use a low-retentive attachment to reduce stress.

Design of an underactuated prosthesis arm

In motion design of a prosthesis arm, number of actuators is considered the most crucial part. The higher number of actuator allows us to have many degree of freedom while results in the heavy weight of the device. In the past, motors and pneumatic systems are commonly used as actuators for prosthesis devices. Albeit easy to control and fast response, motors have limitation that single motor can only control one degree of freedom for full performance of motion. Hence, seven degrees of freedom arm requires a large number of actuators. For application like prosthesis arm, the heavy and bulky size of the prosthesis mechanism is therefore not practical for daily usage. In order to reduce the number of actuator and the weight of prosthesis, we propose a design of an underactuated system for a prosthesis arm with three degrees of freedom motion. The design focuses on the case of shoulder disarticulation. The prosthesis arm has 2 degrees of freedom at shoulder and 1 degree of freedom at the elbow. The mechanism consists of gearboxes and a pulley for force transmission. The mechanism was controlled through a closed loop position control. The prosthesis was made of PLA and aluminum and the total weight is 1.7 kg. The designed prosthesis is capable for posture such as eating, drinking and carrying object of weight not exceed of 1 kg. The range of motion showed that angles of arm can be moved +/- 87° in up and down rotation+/-37° in forward and backward rotation, and the elbow can rotate+/- 40°.