Page 695 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 681
are floating (not connected), it is assumed that the H-bridges are enabled. Input channels
(TTL level signals) INPUT1 and INPUT2 control the direction and magnitude of current
in one of the H-bridges. Once an H-bridge is enabled, the current is controlled by the pair
of INPUT (1/2 or 3/4) pins for that H-bridge. By modulating the pulse width of the INPUT
lines, the average current can be controlled by an external microcontroller.

8.7 LINEAR MOTORS

In principle, all of the rotary electric motors can be designed and manufactured as linear
electric motors by un-rolling the cylindrical shape of the stator and rotor into linear form.
Such linear motors have rectangular cross-sections and are called flat linear motors.In
addition, the un-rolled linear motor can be rolled back around the axis of linear motion to
obtain a tubular linear motor construction. Such linear motors have circular cross-sections
(Figure 8.57).

N
S
S S
N
Torque
(a)

N S
S N

(b)

N
S
N
S Force
(c)

FIGURE 8.57: Principle of linear
motor construction by un-rolling a
rotary motor: (a) a rotary permanent
N magnet type electric motor (i.e.,
S
N
S brushless DC), (b) un-rolling concept,
(c) flat type linear brushless DC motor,
and (d) tubular type linear motor by
(d) rolling again the flat type linear motor
concept around the axis of its force.