Embedded Systems by Jack Ganssle et al

By Jack Ganssle et al

No less than one poultry species makes use of a spray to dig bugs out of holes in timber. a few primates open difficult shells with branches used as golf equipment. The Attini ant is sort of actually a farmer, cultivating patches of fungus and changing fungi species with different ant colonies. in actual fact Homo sapiens isn't the purely species that makes use of instruments or manipulates the surroundings to serve our ends. 4 billion years of evolution has produced creatures whose health for his or her position in an ecological area of interest has to be augmented by utilizing and construction issues.

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This allows the system to know the absolute starting position of the motor shaft, for cases in which this is important. Figure 1-30 shows the pattern for a section of an absolute encoder. The absolute encoder encodes the opaque stripes in a binary fashion so that the absolute position is always known. com 30 Chapter 1 there are bits of resolution. The figure shows the outer four rings; an encoder with 6 rings would require 6 switches and would divide one revolution into 64 unique codes. An encoder that provides 1024 unique positions would require 10 switches and 10 concentric rings on the encoder disk.

Many motor H-bridge ICs include braking capability. These include the L6201 and LMD18200. The L6201 has two inputs to control the two halves of the bridge circuit. If both inputs are brought to the same level (high or low), the driver will brake the motor. The LMD18200 has a separate input signal for braking. Braking can be used to stop a motor quickly, or to hold it in position. One limitation on dynamic braking as a holding force is that there will be no braking until the EMF generated by the motor exceeds the forward drop of the diode in the braking circuit.

3 Brushless DC Motors Figure 1-23 shows a cross-section of a brushless DC motor. This looks very much like a stepper motor, and in fact a brushless DC motor works much the same way. The stator in this motor consists of three coils (A1/A2, B1/B2, and C1/C2). The coils are connected in a three-phase arrangement, with a common center point. A brushless DC motor is more efficient than a brushed DC motor of the same size. This is because the coils in a brushless DC motor are attached to the case (instead of to the rotor), so it is easier to get the heat generated in the windings out of the motor.

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