Motivation for the work
When we were on training in machine in our office, we are told gave us a drawing to produce a machine shaft. During the process, when we feed in a cut of 10mm to the machine, it would cut 9.5mm and when we wanted to drill a hole at the center of the job, it would drilled it off centered, we called on our supervisor after we have wasted much time, power and materials. Surprisingly, after his supervision, he told us that backlash in the machine is responsible for that and he instructed us to use another machine which we did and got what we need immediately. Therefore, that ugly experience motivated us to research on how to reduce high ripple torque in induction motor which is the main causes of vibrations that lead to the backlash in the industrial machine.
1.2 STATEMENT OF THE PROBLEM
• The statement of the human problem our research work will solve is to reduce backlash in industrial machine.
• Explanation of the problem
Backlash can be defined as the maximum distance or angle through which any part of a mechanical system may be moved in one direction without applying appreciable force or motion to the next part in mechanical sequence and is a mechanical form of dead band. More so, it is any non-movement that occurs during axis reversals. For instance, when x – axis is commanded to move one inch in the positive direction, immediately, after this x – axis movement, these x-axis is also commanded to move one inch in the negative direction if any backlash exists in the x-axis, then it will not immediately start moving in the negative direction and the motion departure will not be precisely one inch.
So, it can cause positioning error on holes location, if the motion required to drill the holes causes a reversal in axis direction, it also causes loses ofmotion between reducer input and output shafts, making it difficult to achieve accurate positioning in equipment such as machines tools etc.
The main cause of this problem electrically is vibrations from electric motor as a result of high ripple torque in the induction motor.
• Benefits of solving the problem
1. High quality products will be produce.
2. Productivity will increase because adjustment and readjustment of machine feeding handle or feeding screw to eliminate backlash have been reduced.
3. Operational cost will reduced.
4. Greater efficiency will be guaranteed.
5. Greater accuracy and precision of product will be guaranteed.
6. Wasting of materials will be highly reduced.
1.3 RESEARCH OBJECTIVES
1. To develop a model that will control the error to achieve stability using DTC and fuzzy logic with duty ratio.
2. To determine the error in the torque of the machine that causes vibration which lead to backlash that result in production of less standard products.
3. To determine the position of the stator flux linkage space vector in the poles of the induction motor.
4. To determine the stator linkage flux error in the induction motor that also causes vibration.
5. To simulate the model above in the Simulink environment and validate the result.
1.4 SCOPE AND LIMITATION OF THE WORK
This project work is limited to the use of fuzzy logic controller with duty ratio to replace the torque and stator flux hysteresis controllers in the conventional DTC techniques. The controllers have three variable inputs, the stator flux error, electromagnetic torque error and position of stator flux linkage vector. The inference method used was the Mamdam fuzzy logic inference system. The deffuzzification method adopted in this work is the maximum criteria method.
1.5 SIGNIFICANCE OF THE WORK
The importance of this work in industry where induction motor drives are mainly in application cannot be over emphasis.
As earlier noted, induction motors because of their ruggedness simple mechanical structure and easy maintenance; electrical drives in industries are mostly based on them.
Also, a wide range of induction motor applications require variable speed, therefore induction motor speed, if not accurately estimated will affect the efficiency of the overall industrial processes. Equally, the harmonic losses if not put in check will shorten the life span and efficiency of the motor inverter.
Based on the above, it is aimed at reducing the principle causes of the inefficiency in the DTC induction motor and improves the performance of the system.
1.6 ORGANIZATION OF THE WORK
The work is organized into five chapters. Various control techniques were discussed in chapter two, in chapter three, we discusses the methodology, design and implementation of the direct torque control of induction motor using fuzzy logic with duty ratio controller.
Chapter four discusses data collection, analysis and the simulated results showing the system using conventional method of control and the proposed fuzzy logic with duty ratio method of control under applied load torque conditions.
Conclusion, recommendations and suggestion for further work are mentioned in chapter five.