CLAW TOOTH PM MOTOR
This is another type of stepping motor. This is also known as can-stack Stepping motor, as the stator of this motor consists of a sort of metal can. Teeth are punched out of a circular metal sheet and the circle is then drawn into a bell shape. The teeth are then drawn inside to form claw teeth. A Stack of the stator is formed by joining two bell shaped casings so that the teeth of both of them are intermeshed and the toroid coil is contained within them
This type of motor shown in fig 2.14 is usually of two stacks. Since the rotor has magnetic poles that are axially aligned and is common for both stator stacks, the stator tooth pitches are misaligned by a quarter pitches between the two stacks.
The sequence of excitation is shown in fig. when phase A is excited, the rotor moves by the tension of magnetic lines (state 1).state 2 is the equilibrium position with phase A excited. Next if current is switched to phase B , the rotor will be driven further in the same direction, because the stator teeth in stack B are misaligned by a quarter tooth pitch to the left
with respect to the teeth in stack A. State 3 shows the result due to this excitation. To advance the rotor further to the left and place in the next state (4), phase B is de-energized and phase A is excited. Next, current will be switched to phase B.
The claw tooth motor has low manufacturing cost through it cannot realize a very small step angle.