Designing a Control for a Material Fatigue Testing Machine E-Book

Jörg Henseler

• Herausgeber: GRIN Verlag
• Sprache: Englisch

Veröffentlichungsjahr: 2002

Beschreibung

Diploma Thesis from the year 2001 in the subject Electrotechnology, grade: 1,3 (A), University of Kaiserslautern (Escuela Superior de Ingenieros de Sevilla, Spain), course: Semester Final Paper, language: English, abstract: PROJECT DESCRIPTION One main field of activity of the Department of Mechanical Engineering and Material Science at the Escuela Superior de Ingenieros de Sevilla is material fatigue testing. In order to evaluate material characteristics under specified conditions, material probes are outset to biaxial movements, i.e. traction or pressure, and torsion. The machines for this particular application typically use hydraulics for the power generation; the exact movement is achieved by servo-ventils. Industrial manufacturers demand at least 300.000 € for building a machine like that. This appears very expensive, keeping in mind the very basic task of the machine. Whereas a university of western industrialized countries may bear inversions like that, for universities of third world it is hardly possible to procure such a machine. This was the motivation for the Department of Mechanical Engineering and Material Science at the Escuela Superior de Ingenieros de Sevilla to start a project in order to find a cheap as well as reliable solution for biaxial material fatigue testing. [...]

Leseprobe

Table of Content

Chapter

3.1 Types

3.1.2 Unipolar Motors

3.1.3 Bipolar Motors

3.1.4 Multiphase Motors

3.2 Stepper Motor Parameters

3.3 Characteristics of the particular motors chosen

4.1 H-Bridge

4.1.1 Switching elements: IGBT vs. MOSFET

4.1.2 Low-side Switch

4.1.3 High-side Switch

4.1.4 Circuit design of the H-Bridge

4.2 Short Circuit Avoidance

4.3 Current Control

4.3.1 Pulse Width Modulation

4.3.2 The 555 timer circuit

4.3.3 Reference Voltage

5.1 Moore Machine

5.2 Step Synthesis

5.3 Sequential Logic

5.4 Reset and Enable

5.5 Interface

6.1 Timing Devices

6.1.1 Interrupts

6.1.2 Timing Hardware

6.1.3 Timing Routines

6.1.3.1 The Procedure SetTimerSpeed

6.1.3.2 The Function GrabTimer

6.1.3.3 The Procedure SetTimerHandler

6.1.3.4 The Procedure InternalHandler

6.1.3.5 The Procedure DisableHandler

6.1.3.6 The Procedure NormTimerSpeed

6.1.3.7 The Procedure ResetTimer

6.2 I/O-Management

6.2.2 The Parallel Port

6.2.3.1 The Procedure MotorWrite

6.3 Control Routines

7.1 Turbo Vision

7.2 The TFatigueControl Object

7.2.1 Desktop and Menu Design

7.2.2 Options-Window

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Approved by ___________________________________________________

Escuela Superior de Ingenieros de Sevilla, Spain

Accredited by ___________________________________________________

University of Kaiserslautern, Germany

Date _________________________________________________________

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LIST OF FIGURES

Number Page

1.1. Biaxial Material Fatigue Testing Machine 3

2.1. Main Concept 5

3.1. Schematic of a variable reluctance stepper motor 7

3.2. Schematic of a unipolar stepper motor 8

3.3. Schematic of a bipolar stepper motor 9

3.4. The two control sequences of bipolar motors 10

3.5. Half step modus 10

3.6. Schematic of a multiphase stepper motor 11

4.1. H-Bridge 14

4.2. Symbol of an n-channel MOSFET 15

4.3. Symbol of an n-channel IGBT 15

4.4 H-Bridge circuit diagram 19

4.5. Forward mode 20

4.6. Fast decay mode 21

4.7. Dynamic braking mode 21

4.8. Short circuit avoidance 23

4.9. Pulse Width Modulation 24

4.10. Current mode control 25

4.11. Pin specification of a 555 26

4.12. 555 circuit 27

4.13. Reference voltage circuit 28

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Number Page

5.1. Moore machine state diagram 32

5.2. KV-Diagram for X1* 34

5.3. KV-Diagram for Y1* 34

5.4. KV-Diagram for X2* 35

5.5. KV-Diagram for Y2* 35

5.6. Sequential logic 36

5.7. KV-Diagram for the decrease signal 37

5.8. Mid-level control circuits 39

X.1. Assembly Top Layer 41

X.2. Top Layer Routes 42

X.3. Assembly Bottom Layer 43

X.4. Bottom Layer Routes 44

X.5. Simulation Result Example 45

6.1. Interrupt driven program control transfer 48

6.2. Interrupt Vector Table 49

6.3. 8253/8254 Programmable Interval Timer 51

6.4 Circuit diagram for an ISA I/O-card 58

6.5 Assembly Top View of the ISA I/O-card 60

6.6 Routes on the top layer of the ISA I/O-card 61

6.7 Routes on the bottom layer of the ISA I/O-card 62

6.8 Status window 71

7.1 Desktop 79

7.2 Options window 82

Page 6

Page 7

One main field of activity of the Department of Mechanical Engineering and Material Science at the Escuela Superior de Ingenieros de Sevilla is material fatigue testing. In order to evaluate material characteristics under specified conditions, material probes are outset to biaxial movements, i.e.

•traction or pressure, and

•torsion.

The machines for this particular application typically use hydraulics for the power generation; the exact movement is achieved by servo-ventils. Industrial manufacturers demand at least 300.000 € for building a machine like that. This appears very expensive, keeping in mind the very basic task of the machine. Whereas a university of western industrialized countries may bear inversions like that, for universities of third world it is hardly possible to procure such a machine.

This was the motivation for the Department of Mechanical Engineering and Material Science at the Escuela Superior de Ingenieros de Sevilla to start a project in order to find a cheap as well as reliable solution for biaxial material fatigue testing.

The main change in respect to the up to now common machine design (an example is shown in figure 1.1) is that the biaxial movement of the machine to be build shall be realized by two stepper motors. This evokes two main advantages:

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•From the mechanical point of view, the power transmission becomes easier: The deviation via the pressure generation is no longer needed, instead the power of the stepper motors can be transformed by screws into the desired movement.

•Regarding the control, stepper motors give the opportunity of a precise movement without the necessity of a control loop.∗Most of

all the costs of sensors (most suitable would be LVDT’s) can be avoided in this way.

The project was divided into two main parts, each of them treated by a student with a related field of studies:

•The mechanical part: A student of Mechanical Engineering was to design the mechanical structure of the machine, including the selection of suitable stepper motors.

•The control part: As a student of Electrical Engineering it became my part to design the control for the machine.

The components of the control were not specified. However, certain parts were strongly recommended:

•For high-level control old computers (80286-80486) should be used; these are easily to get for free, as they are no longer useful for modern office applications.

•The control must be simple as well as robust.

•Regarding the low target costs the control should consist of as few components as possible.

∗Chapter 3 will explain the principle of stepper motors and their advantages.

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In order to reduce the complexity of the given task the control is divided into three categories:

•Low-level control:

It is responsible for the current supply of the motors. Additionally, it includes sequential logic for short circuit avoidance.

•Mid-level control:

It has two main tasks: Keeping track of the motor state and providing four input lines: Clock, Direction, Enable and Reset.

•High-level control:

It gives the reset impulse within an initialisation process and continuously takes three main decisions:

Last but not least, a Human-Machine-Interface is provided. Within a Turbo Vision Desktop the user will be able to give exact movement orders and to be informed about the actual state of the system.

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A schematic view of the hierarchic control system is shown in Figure 2.1. The arrows indicate that it is an open-loop control, because there is nothing like a feedback.