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Laddas ned direkt. Comprehensively covers the key technologies for the development of tactile perception in minimally invasive surgery Covering the timely topic of tactile sensing and display in minimally invasive and robotic surgery, this book comprehensively explores new techniques which could dramatically reduce the need for invasive procedures.
The tools currently used in minimally invasive surgery MIS lack any sort of tactile sensing, significantly reducing the performance of these types of procedures. The LVDT core is usually coupled with a linear elastic element. When a force is applied and causes the elastic element to deform, the position of the LVDT core will change allowing an analog signal to be generated in proportion to the applied force.
This sensing scheme is capable of providing accurate measurements and can even resolve millinewton forces. More advanced techniques eliminate the use of the real elastic element but simulate its characteristics in a servo system. An approach to measure forces in a teleoperated force reflecting endoscopic grasper FREG. This actuator is connected with a high-resolution position encoder and a proportional-derivative PD controller to form a servo control configuration.
The proportional gain incorporated with an appropriate derivative gain of the controller was set such that it effectively and efficiently simulates a high mechanical stiffness characteristic, as usually required to ensure transparency in a force feedback system. Thus, the real mechanical elastic element was not used but the servo was applied to mimic its elastic behavior. Mechanical properties of grasped objects such as tissue hardness can also be felt. Another possibility to measure forces is to detect the current of electric motors actuating particular joints.
If the joints are driven by servo control mechanisms, the value of torques or forces generated by the servo motors can be determined since they are usually proportional to the armature current of the motors.
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Based on this principle, a force exerted on the motor axis could be considered as a disturbance of the servo control system. Any efforts of the controller that attempt to increase the motor current to produce sufficient force for balancing disturbance effects can be interpreted as a magnitude of the force being measured.
An alternative way to develop a force sensing device is to make use of pneumatic equipment. Recently, four degree-of-freedom pneumatic-driven forceps that posses force sensing capability have been developed. The forceps consists of four joints, which are driven by wire rope power transmission mechanisms actuated by servo pneumatic actuators.
In this system, the delicate force sensing capability was constituted by introducing a disturbance observer to the pneumatic servo system. The information which is necessary for the estimation of the forceps contact forces such as the differential pressure of the pneumatic cylinders, joint displacements, and joint velocities are supplied to a disturbance observer. Those are further processed by an internal estimation protocol.
The observer makes use of a neural network to estimate possible driving forces of all joints which are then compared with the forces estimated from the measurements of the pneumatic cylinder pressures. The differences indicating the contact forces are low-pass filtered so that the actual contact forces at the forceps tip are effectively predicted.
Performance tests show that the forceps has good sensing ability, being capable of determining contact force values with a resolution of as good as 0. In many applications, most of the force measuring devices use strain gauges as their sensing elements. To provide an accurate means of force measurement, the strain gauge is usually bonded to a flexible structure called flexure.nttsystem.xsrv.jp/libraries/85/sap-handy-orten.php
Pneumatic balloon actuators for tactile feedback in robotic surgery
When a force causes strain in the structure, the electrical resistance of the strain gauge will change allowing the applied force to be electrically measured. However, because the underlying principle of the strain-gauge measurement is based on the measurement of the structural deformation, there is always a tradeoff between the stiffness of the structure and the sensitivity of the measurement. In robotic systems, for instance, high stiffness characteristic of the structure is substantial for sustaining mechanical linkages, working instruments, and objects being manipulated.
Unfortunately, stiff structures tend to provide low measurement sensitivity. Another phenomenon that restricts flexibility of the sensing device design is hysteresis. To prevent possible unwanted effects caused by such phenomenon, a monolithic flexure made of a single piece of metal, is usually exploited.
In MIS, developing a force sensing device is even more challenging since limitations in size greatly restrict the flexibility of sensing device design. At the University of Washington, however, strain gauges were applied in a motorized endoscopic grasper MEG for measuring forces and tissue properties. The pulley does not pass through the instrument insertion port but is linked to the jaws at the instrument tip by a linear translation linkage. A brushed DC motor equipped with a digital encoder was installed to motorize all these mechanisms.
Because the strain gauges, motor, and other electric components always lie outside the abdominal cavity, they need not to be sterilized. Only the interchangeable laparoscopic instrument shaft is needed to be dismounted and autoclaved afterwards. The development of force sensing instruments based on strain gauge technology has also been conducted at John Hopkins University. Recently, a two degree-of-freedom force sensing sleeve that can be integrated with a variety of 5 mm laparoscopic instruments has been developed.
Strain gauge sensing also provides solutions to even more complex force measurements. At the German Aerospace Center DLR , a distal force-torque sensor for laparoscopic instruments see figure below has been developed. The sensor makes use of a hexapod structure known as the Stewart Platform to locate six strain gauges for measuring forces and torques along all of its six measurement axes.
By taking advantage of such a special hexapod structure fabricated from AlCuMg alloy, the sensor has achieved good measurement sensitivity with a very satisfactory structural stiffness characteristic. It can measure forces with a resolution of 0.
Tactile Sensing and Teletaction Research
The whole device has a diameter of 10 mm, which is acceptable for MIS. Recent advances in micro-electromechanical systems MEMS have also contributed to the development of miniaturized force sensing instruments such as sensor integrated forceps, and smart cutting tools. In the industrial sector, Verimetra, Inc. Robotic microforceps and surgical sharps, with strain gauges embedded in their surfaces, were successfully developed on extremely small scale. This demonstrates the great potential of microfabrication technology in the medical area, in particular, for miniaturized MIS-capable smart devices.
Among several sensing principles, capacitive-based sensing is known as one of the most powerful means for detecting extremely small deflections of structures. For many applications which require better performance than strain gauge sensing can provide, capacitive sensing schemes represent an alternative, offering very good sensitivity to very small deflections without direct temperature dependence. Based on the capacitance measurement principle, researchers at Harvard University have developed a remote palpation system, which was intentionally designed for helping the surgeons to search for hidden arteries and tumors buried inside tissues during MIS procedures.
The sensing component of the system is a capacitive tactile array sensor made of two cross layers of copper strips.
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All of these are separated by thin strips of silicone rubber. When a force is exerted above the crossed strip structure, the distances between the copper strips will decrease causing changes of the capacitance values. The capacitance changes measured at all crossing points were then used to determine a spatially distributed set of forces with a possible resolution of as good as 0.
The entire tactile array sensor was placed on a handheld laparoscopic palpation instrument allowing the surgeon to press the sensor against the surface areas of interest.
With specially designed electronics and a computer-based signal processing system, various forms of delicate palpation information such as variations in pulsatile pressure of arteries, stiffness, and texture of soft tissues could be read out and conveyed to the surgeon by either a visual or an intuitive tactile display. Piezoelectric materials have also been considered as potentially effective sensing elements in tactile sensors. If well fabricated, they are able to provide several advantages over other types of sensing devices.
For instance, they can sensitively generate voltages when their structures are deformed due to compression. Although an extremely small deformation is caused by a small punching force, a large output voltage can be generated. The capability to produce voltages distinguishes piezoelectric sensors from most other sensors.
Since no electrical power is needed to be supplied to the sensing elements, their operations are considered very reliable and the application range is greater than with other sensors. One of the many piezoelectric materials is the polymer, polyvinylidene fluoride. For an application in MIS, such material was applied in the development of a micromachined tactile sensor that can be equipped with a jaw of endoscopic graspers. The sensing element, a PVDF film, was attached with a number of patterned aluminum electrodes.
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