NC gringing machine--implementation onto classic machine.

Ciofu, Ciprian ; Carausu, Constantin ; Nedelcu, Dumitru 等

1. INTRODUCTION

Today's modern machinery are CNC (Computer Numeric Control) milling machines and lathes. A microprocesser in each machine reads the G-Code program that the user creates and performs the programmed operations. Personal Computers are used to design the parts and are also used to write programs by either manual typing of G-Code or using CAM (Computer Aided Manufacturing) software that outputs G-Code from the users input of cutters and toolpath (Vilan, 2002).

An entire manufacturing technology known as CAD/CAM has developed around the NC concept and, in addition, CNC with its powerful microprocessors and other enabling technologies proffered from the personal computing phenomenon has enabled the NC concept to branch into many variants, even a variant that is essentially record/playback. The latter of which are known in the industry as "teach lathes".

2. INFORMATION

The adopted constructive solution is refered to realise a conversion of a grinding equipment for profiled surfaces with manual control into a NC equipment.

In figure 1 is presented the general view of the transformed grinding equipment. This one is composed by a computer, NC drivers and steppers motors connected to profiled grinding machine through a positioning and clamping device (figure 3).

Mach 3 (http://www.machsupport.com/) is the software package used to translate 2D drawing and to send the G code date to the drivers. The operator uses a CAD and CAM software to execute the 2D drawing and NC program.

The stepper motor has a wide use through his abilities of digital functions. This abilities was proved by wide use of the integrated electronic in machine controls.

The stepper motor is used in numerical control of the machine because it has abilities of the digital-analog electromechanical transformer.

The stepper motor relised the direct transforming of the entrance signal, in digital form, to an by step angular or incremental movement. In this manner the movement of the machine is realized in discontinuous displacement concording through discret command signals. This solutions has the advantage of use as it is without reaction loops for movement control.

An other advantage of this technical solution is low cost of the implementation of this kind of control devices. This advantage is used to implement this kind of solutions into technological educations.

[FIGURE 1 OMITTED]

The main disadvantage of this system is low efficiencies and high vibrations through his oscillator behavior.

In figure 2 is presented the drivers unit photo.

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An DC power supply is used to charge the stepper drivers.

The steppers motors (http://en.wikipedia.org/wiki/ Stepper_motor) are protected by a mechanical safety system for the case of the stuck of the machine spindle (Picos, et. al, 1992).

The draw of the pieces which was machined was realized with AutoCad software. The draw in autocad was printed on a scale of 20:1--machine optical system scale. This printed draw was used to check in real time the movements of the grinding machine.

To control the machine with Mach 3 Software we obtain the G-code for our draw using LazyCam software. This one convert the .dwg (.dxf) format of the AutoCad draw into G-code.

Mach 3 is a software package which runs on the normal computer, with Windows operating system, 1 GHz processor, 1 Gb RAM and 1024 x 768 pixels resolution. It is preferred to use a desktop system instead a notebook.

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This can be used for an other function i.e. to drawing into a CAD/CAM software when Mach 3 is not running.

The data are send from the PC to driver through parallel or serial port.

In figure 4 and figure 5 is presented the grinding process of the profiled grinding machine during the NC control.

To put in value the advantage of the NC machine versus initial control of the grinding machine we made parts on both system and compare them.

The results shown contignous surfaces on computer controlled.

In future, on this machine could be implemented some automatizations systems like: dimensions controls, controls in real time of the movments e.g.

To test the comportament of the machine with this new equipment mount on it, we execute a lot of pieces using manual control of the machine--the original system, and computer control of the machine--using stepper motors.

At the end, we observe two main advantages: a superior quality of the surfaces and a higher precision for samples obtained using computer numerical control.

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3. CONCLUSION

The presented technical solution has follow advantages:

--working parameters ar controlled by computer

--dual working system

--PC control interface to guide the operator during working process

--axis positioning

--ISO, HPGL eg. programing

The main disadvantages of this adopted solution are:

--the clamping system for the piece is manual

--axis limit is manual

--is difficult to identify zero point

--this system does not have a real time wear compensation

This technical solution is the cheapest one possibility to transform an old classical machine in NC machine. This procedure is the most reliable solution for didactical purposes because show the advantages of the computer uses into manufacturing process.

In future, we intend to improve this machine by using a system for real time control of the dimension and shape the grinding wheel.

Also, another improvement it will be a system which should control the real movement of the grinding wheel along X and Y.

After all these improvement will be made, this machine could be implemented in industry with success due to the advantage of precision that could be obtained and also that one operator could control several machines.

Due to didactical point of view, this machine is extremely important to students because they have the acces to a classic machine with manual movement command and also a CNC machine, both in same time.

This technical solution is also usable into smale workshops.

4. REFERENCES

Picos C., Pruteanu O., C.Bohosievici, V. Braha (1992) Proiectarea tehnologiilor de prelucrare mecanica prin aschiere, Mechanical Cutting Technology Design, ISBN 5632-00970-2 vol 1, Chisinau,

Vilan Gh. (2002) Proiectarea unui Circuit de Comanda Pentru un Motor Pas cu Pas, Designing of an Electronic Control Circuit for a Stepper Motor, ISBN 973-32-0772-3 Bucuresti

http://www.grc.nasa.gov/www/RT19934567679/5000/5950yuf mtz.html, Accessed: 2007-02-15

http://www.machsupport.com/, Accessed: 2008-01-15

http://en.wikipedia.org/wiki/Stepper_motor, Accessed: 2007-11-07