Week 6

Question 1

What happens when a current carrying conductor is placed in a magnetic field?

Answer 1

When a current carrying conductor is placed in a magnetic field, the
conductor will experience a mechanical force if any current flowing through
the conductor has a component at right angles to that field

Question 2

What happens when a conductor is moved through a magnetic field?

Answer 2

Similarly, if a conductor is moved through a magnetic field, then any
component of motion perpendicular to that field will generate a potential
difference between the ends of the conductor

Question 3

What is a stepper motor?

Answer 3

A stepper motor is a motor which converts electrical pulses into a series of
discrete angular movements

Question 4

What is the speed of the motor shaft rotation related to?

Answer 4

The speed of the motor shafts rotation is directly related to the frequency of
the input pulses and the length of rotation is directly related to the number of
input pulses applied

Question 5

What are 5 applications of stepper motor?

Answer 5

 Industrial Machines – Stepper motors are used in automotive gauges and machine
tooling automated production equipment
 Security - new surveillance products for the security industry
 Medical – Stepper motors are used inside medical scanners, samplers, and also found
inside digital dental photography, fluid pumps, respirators and blood analysis
machinery
 Consumer Electronics – Stepper motors in cameras for automatic digital camera
focus and zoom functions
 Commercial – computer peripheral applications such as printers, flatbed scanners,
compact disk drives etc.

Question 6

What are the two components of a stepper motor?

Answer 6

Stator

Rotor

Question 7

What is a stator? (2)

Answer 7

 Stator – As the name implies, this is a stationery component
 Each stator is wrapped with multiple windings or phases that will be energized using a
voltage source, initiating current flow through the winding to produce a polarity on
each end or pole of the stator

Question 8

What is a rotor?

Answer 8

Rotor – the rotating component of the motor

Question 9

How does a stepper motor work?

Answer 9

Each end of the stator is magnetized to
opposite poles. Magnetic flux will flow from North to South thereby continuing through the
magnetic rotor to the opposite stator pole. The flux will want to travel the path of least resistance
or decrease the reluctance of the path. Since the rotor rotates, it will align itself to minimize the
reluctance

Question 10

What are the two winding arrangements for electromagnetic coils in stepper motors?

Answer 10

Unipolar

Bipolar

Question 11

What is a unipolar stepper motor?

Answer 11

Unipolar stepper motor has one winding per phase with a center-tap per phase. Hence allows
the current to flow through half of the winding at one time. In this case, a magnetic pole can be
reversed without changing the direction of current

Question 12

What is a bipolar stepper motor?

Answer 12

On the other hand, bipolar stepper motor has a single winding per phase. Bi directional current
will flow through the windings. However, the current in a winding needs to be reversed in
order to reverse a magnetic pole, so the driving circuit must be more complicated

Question 13

How does a unipolar motor work?

Answer 13

the centre-tap lead is connected to a positive voltage

source

Question 14

How does a bipolar motor work?

Answer 14

the current flows through the entire winding at a time. Also, the current is
allowed to flow in both directions through each winding

Question 15

What are the three parts of a basic stepper motor system?

Answer 15

In a stepper motor system, the stepper motor controller, the motor driver and the motor should
all be present in one form or another. Performance of each component will have an effect on
the others

Question 16

What does the controller do in a basic stepper motor system?

Answer 16

The controller will output command pulses that the motor will follow. By altering the
frequency of the pulse train, the controller can instruct the motor to accelerate, run at a speed,
decelerate or stop. A pulse generator must be present, otherwise the motor will not move

Question 17

What does a stepper driver do in a basic stepper motor system?

Answer 17

The function of the stepper driver is to control the magnitude and direction of current flow
into the motor windings. The driver takes the pulses from the pulse generator and determines
how and when the windings should be energised. The windings must be energised in a
specific sequence to generate motion

Question 18

What are the two indications of the strength of a motor?

Answer 18

Holding Torque - The torque a stepper motor requires when powered but not
signalled to rotate

Operating Torque - The torque a stepper motor can apply when experiencing zero
resistance torque

Question 19

What will change the torque of a motor?

Answer 19

voltage