The mobility of animals, including many insects, is typically superior to current legged robots. This fact recommends the use of animal designs in robot. However, the reality of current technology often encourages engineers to use different designs for legged robots than those found in nature. Some robots use mechanisms to couple their joints for the purposes reducing the number of actuators of simplifying the control problem. Actuators are typically heavy and reducing their number can increase the payload or range of a robot.
When early legged robots were developed, computational limitations impeded the use of onboard computers to coordinate many joints. The ASV, Titan IV, and Dino are three of many robots that use pantograph mechanisms to uncouple the vertical and horizontal motions of their feet. Dante II used power screws to achieve large forces with small motors to save weight, but the resulted in slow movements. The K2T carab robot used cables, brakes and clutches to move its 17 joints with just 5 motors. RHEX is a recent robot that adheres to this strategy of simplified mechanical designs. It uses just one motor in each of its six legs to drive each foot in a circular path. It speeds each foot through its swing phase relative to its stance phase so that the robot can walk in insect gaits despite its simple mechanical design. Mechanical coupling and simplicity can ease the development of legged robots. However, the tradeoffs include reduced mobility.
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Robot Design Using Dry Adhesives
A climbing robot design, using dry adhesion forces, has to be developed in order to maximize the effectiveness of the attachment system. In particular there are three main requirements for developing such a robot:
1. Maximize the attachment area.
2. Apply preload between vehicle and vertical surface for increasing the attaching force.
3. Use peel force during the detaching phase.
Two different vehicle concepts were developed. The first one is a wheg (wheel-leg) vehicle that uses legs with adhesive feet for climbing vertical surface. The second one is a tread based locomotive mechanism using a rubber belt in place of a chain tire.
In order to achieve good performances, an optimization analysis was performed. The properties of tail and the position of the center of the mass were optimized. Finite Element Methods (FEM) was chosen for solving and optimizing the over constrained model. In the FEM model, the climbing robots were schematized by means of three beam elements having null masses. The gravitational force was applied in the center of mass of the system.
The results of the optimization correspond to a vehicle having the same dimensions of the developed tank robot. The force varies changing the length and the rigidity of the tail of the model depicture. The attaching force has a monotone behavior with respect to the Young’s modulus but there is a local minimum for the tail length. The optimal tail length should be 0.12 meter long and the Young’s modulus should be the highest possible.
1. Maximize the attachment area.
2. Apply preload between vehicle and vertical surface for increasing the attaching force.
3. Use peel force during the detaching phase.
Two different vehicle concepts were developed. The first one is a wheg (wheel-leg) vehicle that uses legs with adhesive feet for climbing vertical surface. The second one is a tread based locomotive mechanism using a rubber belt in place of a chain tire.
In order to achieve good performances, an optimization analysis was performed. The properties of tail and the position of the center of the mass were optimized. Finite Element Methods (FEM) was chosen for solving and optimizing the over constrained model. In the FEM model, the climbing robots were schematized by means of three beam elements having null masses. The gravitational force was applied in the center of mass of the system.
The results of the optimization correspond to a vehicle having the same dimensions of the developed tank robot. The force varies changing the length and the rigidity of the tail of the model depicture. The attaching force has a monotone behavior with respect to the Young’s modulus but there is a local minimum for the tail length. The optimal tail length should be 0.12 meter long and the Young’s modulus should be the highest possible.
Synthetic Hair Fabrication og Gecko Robot
As a first step in the synthetic Gecko fiber fabrication it is necessary to develop techniques to create the micro and nano-fibers independently. Once this is accomplished, it is possible to begin integrating the two types of fibers into a single process. The final structure will be a micro-fiber with nano-fibers branching out the end of the micro-fiber.
The first fabrication method utilizes commercially available components while the second method utilizes MEMS techniques to fabricate custom master molds. In both methods, liquid polymer is poured over the molds and cured. The cured molded polymer emerged in the desired physical form. It is possible to approximate the physical characteristics of the beta keratin by selecting the proper polymer.
Results from this method are promising. 200nm diameter high aspect ratio fibers have been produced, which are similar to the distal hairs found in Geckos robot. It is clear that there is bunching or matting occurring between the fibers increases, the inter fiber adhesion force surpasses the spring force of the fiber to remain upright and the fibers begin to bunch. This problem is caused by the high aspect ratio of the commercially available nanopore membrane as well as the high density. To avoid this bunching issue, a second method of fabrication was developed in which the density, diameter and length could be independently controlled. This method entails patterning a silicon wafer through photolithography and using a deep reactive ion etch to create a negative mold for the fibers.
The first fabrication method utilizes commercially available components while the second method utilizes MEMS techniques to fabricate custom master molds. In both methods, liquid polymer is poured over the molds and cured. The cured molded polymer emerged in the desired physical form. It is possible to approximate the physical characteristics of the beta keratin by selecting the proper polymer.
Results from this method are promising. 200nm diameter high aspect ratio fibers have been produced, which are similar to the distal hairs found in Geckos robot. It is clear that there is bunching or matting occurring between the fibers increases, the inter fiber adhesion force surpasses the spring force of the fiber to remain upright and the fibers begin to bunch. This problem is caused by the high aspect ratio of the commercially available nanopore membrane as well as the high density. To avoid this bunching issue, a second method of fabrication was developed in which the density, diameter and length could be independently controlled. This method entails patterning a silicon wafer through photolithography and using a deep reactive ion etch to create a negative mold for the fibers.
Gecko Surface Climbing Robot
For over 2 millennia, humans have watched lizards and bugs scale vertical surfaces in awe. Only recently the attachments mechanisms of these animals have been understood. It is now possible to use similar mechanisms to allow robots to climb in the same manner as these animals.
Robot Geckos ability to climb surfaces, whether wet or dry, smooth or rough, has attracted scientists attention for decades. By means of compliant micro/nano-scale high aspect ratio beta-keratin structures at their feet, geckos manage to adhere to almost any surface with a controlled contact area. It has been shown that adhesion is mainly due to molecular forces such as van der Waals forces.
The Geckos ability to stick to surfaces lies in its feet, specifically the very fine hairs on its toes. There are billions of these tiny fibers which make contact with the surface and create a significant collective surface area of contact. The hairs have physical properties which let them bend and conform to a wide variety of surface roughness, meaning that the adhesion arises from the structure of these hairs themselves.
The structure of the biological Gecko foot-hair is very complicated and miniscule. Each fiber is made from multiple sections. Each fiber consist of a micro hair which is roughly 5 microns in diameter, and atop each of these micro-fibers sit hundreds of nano-fibers which are 200 nanometers in diameter. There are between 100 and 1000 nano-fibers on the end of each micro-hair.
Robot Geckos ability to climb surfaces, whether wet or dry, smooth or rough, has attracted scientists attention for decades. By means of compliant micro/nano-scale high aspect ratio beta-keratin structures at their feet, geckos manage to adhere to almost any surface with a controlled contact area. It has been shown that adhesion is mainly due to molecular forces such as van der Waals forces.
The Geckos ability to stick to surfaces lies in its feet, specifically the very fine hairs on its toes. There are billions of these tiny fibers which make contact with the surface and create a significant collective surface area of contact. The hairs have physical properties which let them bend and conform to a wide variety of surface roughness, meaning that the adhesion arises from the structure of these hairs themselves.
The structure of the biological Gecko foot-hair is very complicated and miniscule. Each fiber is made from multiple sections. Each fiber consist of a micro hair which is roughly 5 microns in diameter, and atop each of these micro-fibers sit hundreds of nano-fibers which are 200 nanometers in diameter. There are between 100 and 1000 nano-fibers on the end of each micro-hair.
Wall Climbing Robot for Thin Surfaces
The robot described here was designed for inspecting gas tanks that are made out of thin metal sheets and are installed in huge ships. From time to time, they have to be analyzed for leaks, especially at the welds. For doing this, helium is injected n the surrounding structure from outside. A sensor that can detect this helium then is move to all places inside the tank to find the position of the leak. Until now, this sensor was carried by a balloon that was operated manually, using some ropes. As this method was very slow and imprecise, a better inspection system, preferably consisting of a climbing robot on magnetic wheels, had to be developed.
As the environment can not support much force, the main goal was to make this robot as light as possible. And other consideration is the surface also considered to be very fragile. To simplify the control and increase the reliability, another method was using only few actuators. To ensure a correct functionality, the most critical risks were analyzed. This analysis does not only incorporate the possibility of some components within the robot breaking down. It also account for the risks of plastically deforming the environment, falling or slipping.
As the environment can not support much force, the main goal was to make this robot as light as possible. And other consideration is the surface also considered to be very fragile. To simplify the control and increase the reliability, another method was using only few actuators. To ensure a correct functionality, the most critical risks were analyzed. This analysis does not only incorporate the possibility of some components within the robot breaking down. It also account for the risks of plastically deforming the environment, falling or slipping.
Clinical Implementation and Acceptance Issues on Robotic Surgery
Safety is an obvious concern for robotic surgery, and regulatory agencies require that it be addressed for every clinical implementation. As with most complex computer controlled systems, there is no accepted technique that can guarantee safety for all systems in every circumstance. Various robotic systems approach the problem in different ways. One common technique is to include passive and active safety mechanism in the mechanical design of the manipulator.
The end of the robot arm is attached to the endoscope through a gimbal and a magnetic coupling. Because the incision prevents lateral motion of the endoscope tube, as the robot moves the endoscope in space above the patient, the gimbal allows the endoscope tube to pivot about the incision. This makes it impossible for the robot to apply lateral forces on the incision. The magnetic coupling acts as an emergency release: if forces on the endoscope exceed the magnetic holding force, the endoscope disconnects and falls onto the patient’s abdomen, which is unlikely to cause injury.
Safety features of the software portion of the systems are also essential. In the context of a urology robot, it is used mathematical logic to analyze program flow and determine if it is possible for control to evade the safety features incorporated into the code. N addition, they implemented a completely independent safety monitor that can arrest a servo runaway and detect out of safe boundary conditions, using joint encoder signals as input.
The end of the robot arm is attached to the endoscope through a gimbal and a magnetic coupling. Because the incision prevents lateral motion of the endoscope tube, as the robot moves the endoscope in space above the patient, the gimbal allows the endoscope tube to pivot about the incision. This makes it impossible for the robot to apply lateral forces on the incision. The magnetic coupling acts as an emergency release: if forces on the endoscope exceed the magnetic holding force, the endoscope disconnects and falls onto the patient’s abdomen, which is unlikely to cause injury.
Safety features of the software portion of the systems are also essential. In the context of a urology robot, it is used mathematical logic to analyze program flow and determine if it is possible for control to evade the safety features incorporated into the code. N addition, they implemented a completely independent safety monitor that can arrest a servo runaway and detect out of safe boundary conditions, using joint encoder signals as input.
Technical Issues Sensing and Control on Surgery Robotics
In tele-operated systems for minimally invasive or microsurgical procedures, there is substantial room for improvement of control and sensory feedback interfaces. In general, the human factor aspects of these systems have been little studied. Research questions include mater manipulator configuration, mapping between master and remote robot coordinate systems, scaling laws for micromanipulation systems, and video, force, and tactile feedback fidelity and bandwidth requirements.
Image-guided procedures have been an area of great success for robotic surgery, but there are many unresolved issues. Improved automatic segmentation and planning systems promise to improve efficiency and accuracy. Areas for improvement in registration include elimination of invasively placed fiducials and methods for non-rigid registration and tracking of tissue deformation in real time. The use of 2D imaging modalities such as ultras sound in combination with 3D tracking may lower costs and enable wider application of image-guided techniques.
For autonomous robotics in general, almost all successful applications over the past three decades have come in areas where tasks are narrowly specified and the environment is predictable, as in manufacturing. The early success of robotics in orthopedic surgery is due at least in part to the fact that bones are essentially rigid and relatively straightforward to manipulate, immobilize and cut.
Image-guided procedures have been an area of great success for robotic surgery, but there are many unresolved issues. Improved automatic segmentation and planning systems promise to improve efficiency and accuracy. Areas for improvement in registration include elimination of invasively placed fiducials and methods for non-rigid registration and tracking of tissue deformation in real time. The use of 2D imaging modalities such as ultras sound in combination with 3D tracking may lower costs and enable wider application of image-guided techniques.
For autonomous robotics in general, almost all successful applications over the past three decades have come in areas where tasks are narrowly specified and the environment is predictable, as in manufacturing. The early success of robotics in orthopedic surgery is due at least in part to the fact that bones are essentially rigid and relatively straightforward to manipulate, immobilize and cut.
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