In a new application of field emitter arrays (FEAs), a unique, ultrahigh-sensitivity, flat image sensor that consists of an FEA and a avalanche-mode photoconductive target is proposed.We have been working to develop highly sensitive camera tubes with a high-gain avalanche rushing amorphous photoconductor (HARP) target. Although our latest HARP tube is about 100 times as sensitive as a conventional solid-state image sensor, it suffers from drawbacks related to its length (about 100 mm) and power consumption. To overcome these problems and develop a next-generation, ultrahigh sensitivity, flat image sensor, we have developed an FEA image sensor.The configuration and operating principle of an FEA flat image sensor are shown in Fig. 1. The sensor consists of an FEA, a mesh electrode, and a HARP target, facing each other in close proximity. The FEA acts as an electron source and the mesh electrode accelerates electrons emitted from the field emitters and suppress their divergence. The HARP target converts incident light to electric charges and multiplies them through an intemal avalanche multiplication effect. A video signal is obtained, pixel-by -pixel, through the recombination of the two-dimensional charge (hole) pattem accumulated on the HARP target and the electrons emitted from the FEA. Figure 2 shows a prototype FEA image sensor. The prototype is only 10 mm thick and has 128 horizontal and 96 vertical pixels. Light output Spindt-type field emitters (a) Configuration (b) Operating principle Fig. 1 Configuration and operating principle of FEA image sensor with HARP target 0-7803-7256-5/02/$10.00 0 2002 IEEE 63
Purpose
There is a growing interest in minimally invasive surgery as interventional radiology (IVR), which decreases the burden on a patient. However, occupational exposure is a problem because the treatment is performed using X-ray fluoroscopic images. This problem can be solved by the development of a teleoperation system, but rapid force presentation is important to perform safe surgery. The purpose of this study is to develop a new teleoperation system that can be controlled at a high speed and can provide feedback force sensation within 20 ms delay.
Methods
A master–slave-type remote-control system for catheterization was developed. A compact and high-speed force feedback system is realized using a novel electro-attractive material (EAM) device by which the resistance force is generated by the magnitude of the voltage applied. The linear and rotational movement of master is transferred to the slave device by UDP communication with the LAN cable, and the same movement is performed by two motors. The collision force of catheter or guidewire, detected by the sensor inside the slave device, is also transmitted to the master device. Two voltage-based methods for EAM: the ON/OFF and linear control methods, were implemented.
Results
After the collision force is detected by the slave sensor, the voltage is applied to the EAM in the master device for an average of 10.33 ms and 15.64 ms by the ON/OFF and linear control methods, respectively. These delays are less than required 20 ms. The movement of the master was stopped by the resistance force of EAM, and that of the slave was also stopped accordingly.
Conclusion
A master–slave-type remote-control system for catheterization that is capable of high-speed force feedback was developed. With a low delay, the developed system achieved the requirements of 20 ms that was aimed for this study. Therefore, this system may facilitate the realization of IVR surgery that is safe for both doctors and patients.
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