Example of Tool with Two Numerical Controlled Axes Tadeusz Mikolajczyk1,a*, Alberto Borboni2,b , Damian Mackowski1,c, Maciej Matuszewski1,d 1
UTP University of Technology and Life Sciences, Bydgoszcz, Poland
2
University of Brescia - Mechanical and Industrial Department, Brescia, Italy
a
[email protected], b
[email protected], c
[email protected], d
[email protected]
Keywords: CNC control, stepper motor, control system, 5 axis machining
Abstract. The paper presents the model of a numerical milling module, expanding its capabilities with two controlled axes. Device through the use of adjustable-tilt construction of two mutually perpendicular rotary axes has free access to any part of the hemisphere. In design used special rotary curvilinear guides with controlled carriage equipped with driven tool. This element was driven by stepper motors controlled with a computer through the special LPT driver and Step2CNC software. Made test confirmed correctness of the presented concept. Introduction One of the trends in the development of machining is to increase the share of machine tool numerical control machining, in more than three axles [1-3]. This is done by using additional rotary axis. The most commonly used configurations with five axes [1-3]. In machining with 5 axial control enables the use of shorter tools [3,4]. With the ability to change the angle of orientation of the tool axis relative to the work piece, surface machining can be performed at the optimum linear velocity which makes the tool life is greatly improved, and the best surface quality is obtained. It also enables the use of higher feed rates, thereby producing a highly effective and precise machining. 5-axis machining can be carried out in two versions as [3]: positioned 5-axis machining, continuous 5-axis machining. In positioning machining was used of recurrent fixed retains the setting head, and then machining operations carried out in this setting. The total processing element is the sum of discrete operations in different orientations of the head. Continuous 5-axes machining allows the user to create paths for 5 axes along with complex surfaces, solids, and meshes. There are three varieties of 5-axis machine tools [2,3]: with table swivel in two axes, the control of torsion table in one axis and headstock too in one axis, with swivel headstock in two axes. Generally, the 5-axis machining is divided into 3 + 2-axis 4+1 and 5-axis [3]. With the 3 + 2 axial milling user can apply the appropriate CAM system programmed tool path to work detail from every charge, every angle and every angle [3]. Machine code is automatically generated, taking into account a fixed axis of rotation and possible detail. Simultaneous 5-axis machining is becoming more widely practiced. It produces cutter freely formed surface while maintaining excellent quality [5,6]. Today, due to the availability of Mechatronic and mechanical components it is possible to construct, and build mini-operated tools and numerical control machine tools driven by stepper motors [7-9], including also 5-axes controlled. Also used modern components to limit deformation
machines [10]. There is also software [11- 13] providing control of such machines. For example, the Step2CNC [11] software can control to 4-axis machining and MACH3 [13] - 5 axis machining. The paper presents elaborated in the Department of Production Engineering at the University of Technology and Life Sciences rotary tilting head with two swivel axes enables extending the kinematical possibilities of numerical machine controlled by 3 axes. Design of tool head An original conception of the tool head structure was elaborated with the possibility of rotation around the point of the tool tip and with the surface of the hemisphere. This is illustrated in schematic in Figure 1. The tool head spindle is equipped with two degrees of freedom, allowing the movement of the tools and guides within the rotation of these guides. This allows depending on the position of the tool tip rotation around a central point or movement on the surface of the hemisphere. This placement is controlled using A and C angles. Radius of hemisphere is defined by the value of the r. Value of radius r can change from 0 to R. Based on the presented concept was developed virtual model of tool (Fig. 2). Guides of the spindle was done using rod diameter O8 mm (S235 steel) respectively bent according to the circle curvature with a specified radius (Fig. 2). The two sections being connected by spacers, which have the function of stiffening the whole structure. After the runners whose are moving truck with the drive spindle head. It was made of sheet aluminum. The consequence of the use of curved guide was impossible to use standard sets of guiding most frequently used in standard designs, including linear ball bearings or shafts supported. In the head are used profiled rollers attached to the truck, which ensured to obtain smooth and backlash-free operation of the tool when moving through the guides. C bearing axis of rotation guides carriage tool hemisphere
A r
Fig. 1. Idea of tool head
R
Fig. 2. Virtual model of tool head
The model presented in Figure 2 was made practically. To drive of the tool was used the stepper motors. For control of C rotation was used stepper motor with extra gear while turnover. Tools tilting with A angle were completed in accordance with the concept presented in Figure 3 by direct coupling gear wheel on the stepper motor axis. Drive truck was built in an original way. Stepper motor mounted on the carriage with an embedded pinion cooperating with a toothed belt adhered to one of the profiles on the side of the outer curve (Fig. 3). Attached to the carriage tool with own drive was made in the form of so-called electro three-phase modeling engine. Because the position of the electro on the carriage is constrained on a hemisphere with radius r (Fig. 1) and can be controlled only by the length of the tool. Made tool was mounted on a manufactured model of CNC machine tool (Fig. 4) or connected with special construction given in Fig. 5.
carriage gear wheel toothed belt rod wheels
Fig. 3. Idea of tools carriage driving
Fig. 4. Tool head mounted on CNC model of machine tool
Fig. 5. Tool head as single construction
Control system The tool was equipped with 2 stepper motors connected to the control card combined with a PC with LPT port. As the motor control card was used model CNC-ALFA-3G (Mixpol-Poland), which can drive bipolar motors rated at 2.5A per phase with variable currents. To control of the tool was used Step2CNC software [11] which can control three linear axes (X, Y, Z) and one rotation (A). To control of the tool was used X linear axis for control A angle of tools tilting (Fig. 1) and Y axis connected to the C stepper motor for head rotation. It is made in dependence of graphical possibilities of Step2CNC software. The PC is equipped with a convenient touch screen to control the directly control software (Fig. 5). Setting of the X and Y parameters in Step2CNC software takes into account the structural parameters of tools design and settings of stepper motor (200 step/rot, microstep). Step2CNC software allows you to work with both: manual using X and Y buttons of the control panel and automatic using included in this software G-code editor (Fig. 6). Linear X axis move for tools tilting with A angle was calculated from the movement of the tool carriage on circle guides: X=3.14*R*Arad where: R - radius of guides curvature, Arad - A tilting angle in rad.
(1)
Because of Arad=3.14*A/180, after substitution Arad to (1) X=3.14*R*
R*A/180*3.14=3.14^2*R*A/180
(2)
In fig. 6b was presented graphical interpretation of written G-code for tool head control. Programmatically, you can also adjust the speed of individual motors and their ratios in order to optimize the performance of the structure. The device attempts After the construction of the head and control system connect the control tests of the tool were performed in manual and automatic mode using Step2CNC software. For manual control of the tool was used manual control panel (Fig. 6a). In automatic mode was used control file written using the G-code (Fig. 6b). In Fig. 6b was shown graphical presentation of G-code execution with used convention (A=X, C=Z).
Manual control panel Visualisation of A rotation
Value of coordination
Start of G-code file
Visualisation of C rotation
Fig. 6. View of screens Step2CNC software (in polish): a) control panel, b) G-code editor
In tests with a manual control found the correct operation of the head rotation and tilting. By setting the appropriate value of the current controller card had sufficient power. Confirmed the viability of the carriage drive, but it seems appropriate to introduce the drive with two gear wheels. This will allow the symmetrical reliable drive of the tilting movement. In the model with a choice of stroke engine (microsteps) theoretically an achievement is possible considerable positioning accuracies about the drive directly to the motor shaft. In practice, the accuracy is limited due to the rigidity of the structure and the resulting backlash associated with the technology of the prototype. In order to carry out the tests written a short program to control the tool head move. To control the rotation parameter A is used, and to control the tilt angle is used in accordance with the connection head X-axis (the Step2CNC support axes including one rotation). The X-axis is calibrated using dependence (1) in accordance with the radius of the guides to obtain an adequate angle of inclination of the tool axis. After the upload the G-code file Step2CNC software started simulation of machining. Device was done properly their tasks, working at the same time smoothly. Discussion and conclusions The developed design of tool controlled with two degrees of freedom is a new solution that provides easy access to the tool's surface of machining. With the use of guides in the shape of a quarter circle with the possibility of trading using stepper motor drive control to make good use of CNC software (Mach3, Step2CNC) for its control. This provides the possibility of tools work programming with the G-code. The device design, allows you to rotate the tool around a point. This requires a positioning of the tool tip axis. This solution allows you to change the tool axis in any direction set by the hemisphere. The developed design enables the transformation numerically
controlled machine tools for 3-axis machine tool in a 5-axis. A disadvantage of the construction is its low rigidity, but the head provided for the processing of polymeric materials. The solution presented standalone tool enables the processing of a hemisphere of radius set by the differences radius guides and distance from the axis of the tool tip guides: where the shape blank can be engraved with an appropriate diameter area. Future developments can include the improvement of kinematical behavior using controlled radius axis in machining. References [1] W. Grzesik, P. Nies ony and M. Bartoszuk, Programowanie obrabiarek NC/CNC. Programming NC/CNC Machine Tools (in polish), WNT Warszawa, 2006 [2] J. Honczarenko J., 2000. Elastyczna automatyzacja wytwarzania-obrabiarki i systemy obróbkowe, Flexible Automation of Manufacturing – Machine Tools and Systems (in polish). WNT Warszawa, 2000 [3] http://www.onlineamd.com/FileUploads/file/WhitePaper-Simplified5AxisMachining.pdf [4] W. Z bala, M. Plaza, Comparative Study of 3- and 5-axis CNC Centers for Free-form Machining of Difficult to Cut Material. International Journal Production Economics, 158 (2014) 345-358 [5] L. T. Tunc, O. Ozkirimli, E. Ozturk, Y. Murtezaoglu and E. Budak, Machining Strategy Development in 5-Axis Milling Operations Using Process Models, Proceedings of 4th CIRP International Conference on High Performance Cutting, 2010 [6] C. S. Juna, K. Chab and Y. S. Leec, Optimizing Tool Orientations for 5-axis Machining by Configuration Space Search Method. Computer-Aided Design, 35/6 (2003) 549–566 [7] L. Kamieniecki,, T. Mikolajczyk, PC Controlled Mechatronics Tool, CIMAC, 7/3 (2012) 199204 [8] T. Mikolajczyk, D. Dorsz, L. Romanowski, Design and Control System of Parallel Kinematics Manipulator. Applied Mechanics and Materials, 436 (2013) 390-397 [9] F. Aggogeri, A. Borboni, A. Merlo, and N. Pellegrini, Machine Tools Thermostabilization using Passive Control Strategies. Advanced Materials Research, 590 (2012) 252-257. [10] A. Borboni, E. Ceretti, A. Copeta, D. Moscatelli, R. Faglia and A. Attanasio, High Precision Machine Based on a Differential Mechanism. ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis ESDA 2014, 2 (2014) 1-7. [11] www.akcesoria.cnc.info.pl/step2cnc.htm [12] www.cnc.pl. [13] www.machsupport.com
