Stepper motors - PowerPoint PPT Presentation

1 / 36
About This Presentation
Title:

Stepper motors

Description:

... have several windings which needs to be energized in correct sequence. ... convert the step signal into winding energizing patterns is called a translator' ... – PowerPoint PPT presentation

Number of Views:674
Avg rating:3.0/5.0
Slides: 37
Provided by: ksp9
Category:

less

Transcript and Presenter's Notes

Title: Stepper motors


1
  • Stepper motors
  • Presented by
  • Vijay Mahadevan
  • Pratik Majmundar
  • Sameer Vaidya
  • Under the guidance of Prof. Rajab Chaloo

2
Basics of stepper motors
  • Incremental motion devices with precise open loop
    positioning capability.
  • Applications probers, plotters, robots, computer
    peripherals and manufacturing systems.
  • Desired motion is obtained through discrete
    increments generated by series of current pulses.

3
  • Advantages low cost, high reliability and
    robustness.
  • When operated in open loop mode, they are prone
    to missing steps, resonance effects and low
    settling times.
  • Therefore closed loop control of stepper motor is
    desired for high performance.

4
Classification of stepper motors
  • Based on construction
  • Based on type of motion

5
Classification based on construction
  • Variable reluctance
  • Permanent magnet
  • Hybrid type
  • Variable reluctance are characterized by absence
    of permanent magnet.
  • Permanent magnet incorporates a permanent magnet
    rotor.
  • Hybrid type makes use of both permanent magnet
    and variable reluctance principles for
    development of torque.

6
Based on type of motion
  • Rotary stepper motors
  • Linear stepper motors

7
Types of linear stepper motors
  • Single axis type motion in two axial direction.
  • Dual axes type along with motion in two axial
    direction, a small rotational (yaw) degree of
    freedom is present.

8
Why do we use stepper motor?
  • Positioning something accurately by using DC
    motor is pretty difficult.
  • DC motors have a very gradual acceleration and
    deceleration curves, stabilization is slow.
  • Adding gearing can help but overshoot is still
    present and will throw off the anticipated stop
    position.

9
  • The only effective solution to use DC motor for
    precise positioning is using servo.
  • But this can get fairly complex and expensive for
    most hobby applications.
  • So what is the solution?

10
  • Stepper motor is the solution to this problem.
  • Stepper motors differ from DC motors in their
    torque speed relationship.
  • Stepper motors can produce highest torque at low
    speed which is not the case in DC motors.

11
  • Another characteristic of stepper motor is
    holding torque which is not present in DC motors.
  • This eliminates the need for gearing mechanism.
  • Stepper motors have several windings which needs
    to be energized in correct sequence.

12
  • If the control signals are not sent in correct
    order, motor may not turn in a rough or jerky
    manner.
  • Circuit which is used to convert the step signal
    into winding energizing patterns is called a
    translator.
  • A driver is also used along with translator to
    handle current drawn by the motor.

13
  • A translator circuit along with driver

14
Common characteristics of stepper motors
  • Voltage It is printed on unit or mentioned in
    the datasheet. It may be exceeded sometimes to
    obtain desired torque.
  • Resistance resistance per winding will determine
    the current draw of the motor and will affect
    torque curve and maximum operating speed.

15
  •  Degree per step It specifies the degrees the
    shaft will rotate for each full step. It can be
    calculated by dividing 360 by the number of steps
    in one complete rotation.
  • Common degrees per step numbers include 0.72,
    1.8, 3.6, 7.5, 15, and even 90.
  • Degree per step is referred to as the
    resolution of the motor.

16
Open-Loop Control of Stepping Motors
  • In general, open loop control in a stepper motor
    is adequate. Why?
  • An exception is under transient conditions near
    rated torque.

17
Block Diagram
  • Hardware approach
  • Software approach

18
Stepper Motor Response
-It is useful to observe the response to a single
pulse input before studying the behavior under
general stepping conditions. - Why do we have
dynamic torque? -The static torque is positive at
the switching point, but is generally not maximum
at that point.
19
Consider the following three phase VR stepper
motor
20
Stepper Motor response to a sequence of pulses.
  • Single stepping cascaded sequence of single
    pulse responses.
  • Slewing motion to achieve slewing motion, motor
    has to be accelerated from a low speed ramping.
    This is accomplished by applying a sequence of
    pulses with a continuously increasing pulse rate
    R(t).

21
Typical slewing response.
22
  • In practice, step rate is often increased
    beyond the slew rate, in a time interval shorter
    than what is specified for acceleration and then
    decelerated to the slew rate by pulse subtraction
    at the end.

23
-In transient operation, non uniform stepping
sequences might be necessary depending on the
complexity of the motion trajectory and the
required accuracy.
-The Electrical Time Constant is given by L/R.

Electrical Time constant L/(R R).
24
Static Position Error
25
Damping in Stepper Motors -
  • Mechanical damping.
  • Electrical Damping.
  • Electronic Damping.

-Advantages and disadvantages.
26
Feedback Control of Stepper Motor
27
Why Feedback?
  • Open loop operation is adequate for low speed and
    steady state operation.
  • Actual response can not be measured.
  • In open loop control significant errors can not
    be measured.

28
(No Transcript)
29
Models of Stepper Motor
  • Simple Model
  • Under steady state operation most of its
    parameters remains constant.
  • Modified Model
  • Under transient and high speed operation assumed
    constant in the torque source model will vary
    with time as well as rotor position.

30
Selection of stepper motor
  • Main requirement of particular application.
  • eg. Speed, acceleration, required accuracy and
    resolution and load characteristics, such as
    size, resistance torques.
  • Compute operating torque and stepping rate for
    particular application.
  • Using torque versus stepping rate curves select
    suitable motor.

31
Applications
  • Printing
  • Disk drives
  • Robotics
  • Automotives
  • Medical and Metallurgical lens drives

32
Advantages
  • Position error is noncumulative.
  • High accuracy is possible.
  • Easy to adopt to digital controlled applications.
  • No serious stability problem occurs.
  • Torque and power requirements can be optimized
    and response can be controlled by electronic
    switching.

33
Disadvantages
  • Low torque
  • Limited speed
  • High vibration

34
Conclusion
35
References-Control sensors and actuators
by Clarence W. deSilva.-http//www.eio.c
om/jasstep.htm
36
Thank you !!!
????
Write a Comment
User Comments (0)
About PowerShow.com