Page 202 - Robotics Designing the Mechanisms for Automated Machinery

!90 Feedback Sensors

FIGURE 5.22 Electromagnetic
device for measuring speed of
rotation (car speedometer).

proportional to the speed of rotation. Therefore, the torque angle of spring 3 and the
rotational angle of indicator 4 are also proportional to the speed of rotation.
The method of length measurement mentioned at the end of the previous section
(5.1) is easily transformed into speed.
Flow-rate sensors are also a kind of speed-measuring device which provide infor-
mation about the flow rates of gases or liquids. Here we consider some ideas used for
this purpose. Figure 5.23 shows an example of a design for an impeller-type sensor.
Impeller 1 (a miniature turbine) rotates in agate bearings 2, installed in supports 3
inside a pipe. Axial displacement is limited by agate thrust bearings 4. The pipe section
and the impeller are made from a nonmagnetic material. A small piece of a magnetic
material 5 is set into one side of the impeller shaft. Outside the pipe a permanent
magnet 6 with coil 7 wound around it is installed. During rotation the impeller's shaft
turns piece 5, and thus the magnetic flux changes depending upon its position rela-
tive to the permanent magnet. This induces an alternate electromotive force of a fre-
quency double that of the impeller's speed of rotation. The rotation speed of the

FIGURE 5.23 Gas or liquid flowmeter with an impeller.