tailieunhanh - robotics Designing the Mechanisms for Automated Machinery Part 7

Tham khảo tài liệu 'robotics designing the mechanisms for automated machinery part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Linear and Angular Displacement Sensors 183 s FIGURE Analog optical displacement sensor. toelectric element that has a variable response to illumination along its surface. When a diaphragm 1 with a narrow slit 2 moves along optical wedge 3 the latter s response corresponds to the relative position of these elements. It is not a highly sensitive device. However there are situations where it is appropriate. Pneumatic sensors We now consider pneumatic sensors. The basic model we will consider is shown in Figure 5. 12. Its main elements are the nozzles in sections I and II. Let US consider the continuity of flow through these nozzles which is described in the following form aifipVi a2f2py2- Í5-14 Here a2 coefficient of flow rates in sections I and II respectively fỉ Ỉ2 cross-sectional areas of the nozzles I and II p density of the gas assumed to be constant Vp v2 velocities of gas flow within I and II H working pressure before nozzle I h working pressure before nozzle II. Now we make some assumptions first that the gas density in the two sections is practically equal second a 2 1- FIGURE LRNt of pneumatic position sensor. 192 Feedback Sensors rate. These devices are suitable for a wide range of flow rates from very small to thousands of cubic meters per hour. The accuracy is 1-2 . To increase the sensitivity of the device and make it suitable for rapidly changing flow rates the thermoresistors must have very small masses to reduce their thermal inertia. Figure schematically shows such a thermoresistor. On a base 1 in the form of a truncated cone made of a material with low heat conductivity a thin 1-mm film 2 of platinum or other metal is applied. The other dimensions of this film are about by 1 mm. The film is provided with leads 3. The plane of the film is oriented according to the flow s speed vector. Such sensors can respond to fast flow changes of up to 100 kHz. Positive displacement devices constitute a special class of flowmeters.