MECHATRONICS THE NEW WAY OF LOOKING AT TECHNOLOGIES

Hello everybody and do we know what’s new in everyone’s mouth whenever anyone starts talking about latest technologies? What is in the mind of everyone at present while they think of new innovations and new technologies? It’s not just the ‘Machines’ or just the ‘Electronics’, any more. Ya there was a time when people used to take and think of these two things in two different phases and think separately, but as we know with each development and new breakthroughs we all want new things, new technologies, new everything which would make our daily works more easier to be done, so that they can be completed in less time and more importantly with less effort. Thus, we just don’t want machine operations to be done at one place and electronic operations to be carried out at different place which lead to the combination of both the technologies and give birth to the ‘Mechatronics’. So, at present scientist all over the world are giving their focus under this topic.

So then, what is Mechatronics? This is a simple question that might arise in most of the peoples mind. Let’s consider the modern auto-focus, auto-exposure camera.

 

To use the camera all one need to do is point at the subject and press the button to take the picture. The camera automatically adjusts the focus so that the subject is in focus and automatically adjusts the aperture and shutter speed so that the correct exposure is given.

Consider a truck smart suspension.  Such a suspension adjusts to uneven loading to maintain a level platform, adjusts to cornering, moving across rough ground, etc. to maintain a smooth ride. Consider an automated production line, such a line may involve a number of production processes which are all automatically carried out in the proper and correct sequence and in the right way. 

 All these automatic cameras, the truck smart suspension, the automated production line are examples of a marriage between electronic control system and mechanical technology.

Such technologies generally use microprocessors as controllers and have electrical sensors extracting informations from the mechanical inputs and outputs via electrical actuators to mechanicla systems. The term mechatronics is used for this integration of microprocessor control systems, electrical systems and mechanical systems. A mechatronic system is not just a marriage of electrical and mechanical systems and is more than just a control system, it is a complete integration of allllllll of them.

Mechatronic brings together areas of technology involving sensors and measurement systems, drive and actuation systems, analysis of the behavior of systems, control system, and microprocessor systems.  That essentially is a summary of this book.

Mechatronic involves of numerous systems. A system can be thought of as a box which has an input and an output and where we are not concerned with what goes on inside the box but only the relationship between the output and the input. Among those numerous systems the most basic but most vital ones are the Measurement systems and the Control systems.

Measurement systems in general are considered to be composed of major three components i.e. sensors, signal conditioners and display

  

1.       A Sensor which responds to the quantity being measured by giving as it’s a signal which is related to the quantity. For example, a thermocouple is a temperature sensor. The input to the sensor is a temperature and the output is an e.m.f. which is related to temperature value.

2.       A Signal Conditioner takes the signal from the sensor and manipulates it into a condition which is suitable for either display, or in the case of a control system, for use to exercise control. Thus, for example, the output from a thermocouple is a rather small e.m.f. and might be fed through an amplifier to obtain a bigger signal. The amplifier is the signal conditioner.

3.        A Display system where the output from the signal conditioner is displayed. This might, for example, be a pointer moving across a scale or a digital readout.

Now lets give some consideration to a ‘digital thermometer’. This has an input of temperature to a sensor, probably a semiconductor diode. The potential difference across the sensor is at constant current, a measure of temperature. This potential difference is then amplified by an operational amplifier to give a voltage which can directly drive a display. The sensor and operational amplifier may be incorporated on the same silicon chip. So a simple looking digital thermometer is a great marvel of mechatronics handed over to us for our daily use.

                Control system, in order to understand control system properly lets take an example of our own body, unless we are ill, our body temperature stays in almost constant temperature regardless of whether we are in a cold or in a hot environment. To maintain this constancy our body has temperature control system. If our temperature begins to increase above the normal then we begin to sweat and if it decreased then we shiver, both of these functions are the mechanisms which our bodies have installed in our body system to restore our body temperature to its normal value. Over here the control system is maintaining constancy of temperature. The system has an input from sensors which tell it what the temperature is and then compares this data with what temperature should be and initiates the appropriate response in order to obtain the required temperature. This is an example of feedback control; signals are fed back from the output, i.e. the actual temperature, in order to modify the reaction of the body to enable it to restore the temperature to the ‘normal’ value. Feedback control is exercised by the control system comparing the fed back actual output of the system with what is required and adjusting its output accordingly.

Feedback control systems are widespread, not only in nature but also in industry. There are many industrial process and machines where control, whether by humans or automatically, is required. For example, there is process control where such things as temperature, liquid level, fluid flow, pressure, etc. are maintained constant. Thus in a chemical process there may be a need to maintain the level of a liquid in a tank to a particular level or to a particular temperature. There are also control systems which involves consistently and accurately positioning a moving part or maintaining a constant speed. This might be, for example, a motor designed to run at constant speed or perhaps a mechanical operation in which the position, speed and operation of a tool is automatically controlled.

Sequential controllers

There are many situations where control is exercised by items being switched on or off at particular preset times or values in order to control processes and give a step sequence of operations. For example, after step 1 is completed then step 2 starts. When step 2 is completed then step 3 starts, etc.

The term sequential control is used when control is such that actions are strictly ordered in a time or event driven sequence. Such control could be obtained by an electrical circuit with sets of relays or cam-operated switches which are wired up in such a way as to give the required sequence. Such hard-wired circuits are now more likely to have been replaced by a microprocessor controlled system, with the sequence being controlled by means of a software programs.

As an illustration of sequential control, consider the domestic washing machine. A number of operations have to be carried out in the correct sequence. These may involve a pre-wash cycle when the clothes in the drum are given a wash in cold water, followed by a main wash cycle when they are washed in hot water, then a rinse cycle when the clothes are rinsed with cold water a number of times, followed by spinning to remove water from the clothes. Each of these operations involves a number of steps. For example, a pre-wash cycle involves opening a valve to fill the machine drum to the required level, closing the valve, switching on the drum motor to rotate the drum for a specific time, and operating the pump to empty the water from the drum. The operating sequence is called a program, the sequence of instruction in each program being predefined and ‘built’ into the controller used.

The system that used to be used for the washing machine controller was a mechanical system which involved a set of cam-operated switches. When the machine is switched on, a small electric motor slowly rotates its shaft, giving an amount of rotation proportional to time. Its rotations turns the controller cams so that each in turn operates electrical switches and so switches on various circuits in the correct sequence. The contour of a cam determines the times at which it operates a switch. Thus the contours of the cams are the means by which the program is specified and stored in the machine. The sequence of instructions and the instructions used in a particular washing program are determined by the set of cams chosen. With modern washing machines the controller is a microprocessor and the program is not supplied by the mechanical arrangement of cams but by a software program.

Microprocessor based controllers

                Microprocessors are now rapidly replacing the mechanical cam operated controllers and being used in general to carry out control functions. They have the great advantage that a greater variety of programs become feasible. In many simple systems there might be just an embedded microcontroller, this being a microprocessor with memory all integrated on one chip, which has been specifically programmed for the task concerned. A more adaptable form is the programmable logic controller.

                                           

                This is a microprocessor-based controller which uses programmable memory to store instructions and to implement functions such as logic, sequence, timing counting and arithmetic to control events and can be readily reprogrammed for different tasks, for control action of a programmable logic controller, the inputs being signals from, say, switches being closed and the program used to determine how the controller should respond to the inputs and the output it should then give.

The automatic camera

                The modern camera is likely to have automatic focusing and exposure. When the switch is operated to activate the system and the camera pointed at the object being photographed, the microprocessor takes in the input from the range sensor and sends an output to the lens position drive to move the lens to achieve focusing. The lens position is fed back to the microprocessor so that the feedback signal can be used to modify the lens position according to the input from the range sensor. The light sensor givens an input to the microprocessor which then gives an output to determine, if the photographer has selected the shutter controlled rather than aperture controlled mode, the time for which the shutter will be opened. When the photograph has been taken, the microprocessor gives an output to the motor drive to advance the film ready for the next photograph.

                The program for the microprocessor is a number of steps where the microprocessor is making simple decision of the form: is there an input signal on a particular input line or not and if there is output a signal on a particular output line. The decisions are logic decisions with the input and output signals either being low or high to give on-off states. A few steps of the program for the automatic camera might be of the form:

                begin

                        if battery check input OK

                                   then continue

                                   otherwise stop

               loop

                         read input from range sensor

                         calculate lens movement

                         output signal to lens position drive

                         input data from lens position encoder

                         compare calculated output with actual output

                         stop output when lens in correct position

                         send in-focus signal to viewfinder display

                         etc.

The mechatronic approach

                The domestic washing machine referred to earlier that used cam-operated switches in order to control the washing cycle is now-­of-date. Such mechanical switches are being replaced by microprocessors. A microprocessor can be just considered as being essentially a collection of logic gates and memory elements that are not wired up as individual components but whose logical functions are implemented by means of software. The microprocessor-controlled washing machine can be considered an example of a mechatronics approach in that a mechanical system has become integrated with electronic controls. As a consequence, a bulky mechanical system is replaced by a much more compact microprocessor system which is readily adjustable to give a greater variety of programs.

In conclusion

Mechatronics involves the bringing together of a number of technologies: mechanical engineering, electronic engineering, electrical engineering, computer technology and control engineering. This can be considered to be the application of computer based digital control techniques, through electronic and electric interfaces, to mechanical engineering problems. Mechatronics provides an opportunity to take a new look at problems, with mechanical engineers not just seeing a problem in terms of mechanical principles but having to see it in terms of a range of technologies. The electronics, etc. should not be seen as a bolt-on item to existing mechanical hardware. A mechatronics approach needs to be adopted right from the design phase. There needs to be a complete rethink of the requirements in terms of what an item is required to do.

                                               

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