- Double claw robotic end-effector design pdf
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- A Novel End-Effector Design for Robotics in Image Guided Needle Procedures
- A Double Claw Robotic End-Effector Design
- Robot end effector
Robotic end-effectors are being developed to facilitate image-guided minimally-invasive needle-based procedures such as tumor ablation, biopsy, thoracentesis, and blood sampling. A novel mechanical end-effector was designed to address the challenges associated with any major needle-based procedure, focusing on liver biopsy and ablation.
In this end-effector embodiment, the distal end of a single articulating arm can grip needles and instruments and allow a fairly high number of degrees of freedom of movement during the complex motions associated with positioning and driving needles, as well as the periodic motions associated with breathing patterns.
Tightening a cable that runs through the articulations fixes the arm in a rigid state, allowing insertion of the gripped needle. In its final form, we diagram a design that will require electro-mechanical stimulation and remote joystick control.
Moreover, we discuss how cranial-caudal motion of soft tissue organs and the associated forces affect design constraints. A simulation protocol describes the use of tissue phantoms with mechanical properties in the range of hepatic tissue and the overlying abdominal wall.
Double claw robotic end-effector design pdf
Finally, an in vivo protocol details the possible use of a robotic arm coupled with our end-effector in an image-guided interventional suite. Such a switchable and flexible mode for a robotic arm overcomes much of the current limitations for automated needle placements for mobile targets, subject to breathing or patient motion and the inherent risks thereof. Liver biopsies provide the level of specificity required to diagnose serious malignant hepatic ailments and their severity.
A percutaneous liver biopsy is conducted through the skin into the liver. The categories of needles that are used in liver biopsies include: suction needles, cutting needles, and spring-loaded coring needles that have a triggering mechanism Fig. Bleeding incidents are related to the duration of needle placement in the liver and larger needle diameters 1. Sixty percent of complications follow approximately two hours post procedure and 96 percent follow within 24 hours post procedure 1.
Continued, severe abdominal pain entails the possibility of a more serious complication, such as bleeding or peritonitis inflammation of the membrane lining the walls of the abdominal cavity. The most serious bleeding complication of percutaneous liver biopsy is intraperitoneal hemorrhage deep-seated abdominal bleeding outside organs.
This usually becomes apparent within the first 2 to 3 hours after the procedure 1. The cranial-caudal motion of the liver during respiration is a likely instigator of bleeding and trauma to hepatic tissue, due to the additive periodic affect of the highly vascularized soft tissue organ interacting with the rigid shaft of a needle.
Today, new robotics-based interventional strategies are being investigated and applied to liver biopsies and tumor ablations. The goal is not physician-intensive or robotics-intensive. Rather, it is physicians utilizing robots to promote accurate and efficient liver procedures.
Because patients lie supine in nearly all CT imaging suites, where the CT modality is used to monitor the needle position in real time, robotic arms are likely to be mounted on the table or ceiling, or on a cranial-caudal moving stereo-tactical frame that may wrap around the body.
These arms will possess articulations and ball and socket joints that allow bending and rotation in several different directions to accomplish tasks. Therefore, such arms will have multiple degrees of freedom.
NASA defines an end-effector as the gripping device that is located at the end of an arm and has an effect such as grasping on objects within its reach 5. For the abdomen, the object is the biopsy or ablation needle. In our view, the end-effector offers a chance to increase the overall degrees of freedom of the arm as a whole.
Moreover, an end-effector with articulations and an ability to tense and relax could perhaps accommodate very well for motions of the liver associated with respiration. The actual gripper at the base of this extended end-effector will provide the means of grasping and releasing the biopsy needles, but the end-effector as a whole could be a part of a localized needle driving mechanism after gross approximate localization via alternate mechanism remainder of arm.
Ex vivo testing on bi-direction moving phantoms with tissue mimicking properties confirms the feasibility of our design. Future pre-clinical testing will involve CT image guided biopsies and ablations conducted on mechanically-ventilated pigs.
An affective end-effector design is able to compensate with the cyclical nature of the forces associated with respiration. The forces that are exerted throughout the respiratory cycle cause shape alterations in soft tissues in the thorax and abdominal regions.
Cranial-caudal shortening greater than 1 cm in length has been observed between CT models extracted from scans during breathing hold at exhale and at inhale states 6. For the initial design speculations, the liver is assumed to undergo small linear and elastic deformations in the cranial-caudal direction. The assumption is made that complex organ shift geometries and deformations are negligible. Two different states of device activity are essential to the design analysis.
If the patient can hold their breadth during the needle driving portion of the procedure; a simple algorithm would permit the physician to maneuver the needle to the point of entry via a coordinate grid. The needle would then enter the liver via a straight line trajectory from the surface entry point. This rigid state of activation must deal with a patient that cannot hold their breadth.
An algorithm which takes into account the sinusoidal nature of the respiratory cycle would then need to be devised. For our calculations, we assume 12 breaths per minute or 0.
Robotic gripper mechanism - robotic gripper design - solidworks assembly of gripper - end effector
Assuming that no phase shift occurs and that the region of interest is displaced from a coordinate grid centered on the cranial-caudal axis, the following sinusoidal function would form the basis for an algorithm to drive a needle in a breathing patient:.
The second state of activation is when the end-effector becomes flaccid, post-needle insertion.
In the simplified bi-directional cranial-caudal model, two degrees of freedom are all that is required. However, the reality of the situation demands many more degrees of freedom. Better estimates of the number of degrees that are sufficient can be made by examining heavy breathing scenarios.
During heavy breathing, extra force is generated via contraction of abdominal muscles, which pushes the abdominal contents upward against the bottom of the diaphragm. Another method of expanding the lungs is to raise the rib cage. In their natural resting position, the ribs slant downward.
The ribs project almost directly forward during elevation 9. Because of the complexities that have just been detailed, overcompensating by maximizing the numbers of degrees of freedom is recommended. The muscles that dominate inspiration are the external intercostals.
Conversely, the muscles that dominate expiration include the abdominal recti and the internal intercostals. The forces that are generated by these muscles have been gleaned from the linear envelopes of EMG signals. As seen in figure 2 , the maximum amount of force that is generated by the external intercostals is approximately N, and the maximum amount of force that is generated by the abdominal recti is approximately 40 N 8.
The latter torque is exerted in opposition to the former torque, and the pivot point is considered to lie at the center of the needle along the axis of the shaft. Therefore, the tension force exhibited in the flaccid state cannot produce a torque that exceeds or equals the torque that accompanies F BR.
On the other hand, when rigidity is desired to hold the needle completely still, static equilibrium must be maintained and enough tension force must be generated in the articulating arm to counter the torque effects of F BR. Once again, the pivot point is assumed to be at the center of the long axis of the needle.
A Novel End-Effector Design for Robotics in Image Guided Needle Procedures
An elastic modulus equivalent to 10 KPa was selected based on values used in previous studies of liver tissue properties 6. The associated ultimate tensile strength and shear strength for liver tissue are 24 KPa and KPa, respectively 9. In order to avoid permanent damage to liver tissue surrounding the needle, a feedback mechanism in the end-effector must guard against pressures in the cranial caudal direction exceeding 10 KPa.
Control mechanisms that maintain a tension in the articulating portion of the end-effector would help to set a safe maximum tension during rigid mode operation.
The design is a robotic end-effector for driving needles during image guided biopsy procedures, in which a single articulating arm, with a needle gripper on its distal tip, tenses and relaxes based on electronic signals conveyed to it via operator instructions.
The arm will be mounted on a stereo-tactic frame Fig. Fixing the arm is accomplished through tensioning of a single cable that runs through the articulations. The articulating arm on the end-effector is comprised of a series of ball and socket links. The links contain a hemispherical protrusion on their proximal ends, and hemispherical indentations on their distal ends. The shapes of the links are identical to promote smooth rotation against one another.
The cable passes through the center of all the links and is connected between the tightening mechanism in the robotic arm and the needle gripper on the distal tip.
Rotation of a triggering mechanism in the arm tightens the cable and forces the links to hold against one another in place. The articulating arm portion will adapt to interface with a variety of grippers, and will not be designed at this point to interface with one specific gripper. However, solely for the purpose of constructing the prototype detailed here, the needle gripper segment of the end-effector was provided by Mondo-tronics Inc. The gripper arms spread up to 3.
An operator can control the gripper via Mini SSC servo controller.
Input at or baud from any PC, Mac, Stamp, et al is possible. Serial Motor Interfaces exists for compatible drivers that can be used for DC motors boards This is ideal for running any robot or system via a serial port and Mini SSCs.
As a result, materials that avoid introducing streak artifacts during CT scanning are preferred. Moreover, MR compatibility of materials would permit a greater range of operating environments.
The articulations might then be produced from rigid plastics that can be laced with glass fiber or carbon re-enforcement to offer a material stiffness that compares with that of metal.
A Double Claw Robotic End-Effector Design
Standard, 6-axis stepper drive electronics are suggested as the means to automate a mechanical prototype for proof of concept testing Fig. The motor connections in this system use standard 9-conductor d-sub cables. Other power speculations include or VAC at Hz. Front panel switches for motor control allow manual control mechanisms access when PC based automation fails.
Standard 3-Axis Stepper Driver Electronics Angular positioning elements spread throughout the articulating joints would greatly aid preserving the degrees of freedom that are inherent in the mechanical design once electrical stimulation is introduced.
Angular positioning elements would also be instituted within the joints of the robotic arm itself and at the interface between the end-effector and the robotic arm. Motion transmission occurs through toothed belts. Manual positioning can be accomplished via hand cranks and graduated dials for manual positioning. Motor system connections are made by 9-conductor d-sub cables Needle driving could be accomplished post-positioning either by the end-effector acting to drive the needle, or by the remainder of the arm driving the rigid end-effector gripping the needle to its target location.
One way to develop the former approach would be to imbed an additional flexible mechanism inside the end-effector that would protrude via servo motors to drive the needle along the trajectory line toward the target point as close to the center of the target as possible. Three-dimensional sensing elements could be located on the tips of the cable and the driving mechanism to ascertain the needle position in real-time.
Another driving solution is to use a linear actuator that utilizes a corkscrew motor.
Robot end effector
The screw is embedded inside an actuator that extends or contracts the needle based on the turning motion of the motor. Most likely, this mechanism would be a part of the gripper. An in vitro protocol must test the ability of the end-effector to adjust to cranial-caudal motion and not tear soft tissue.