The term CNC is the abbreviation of Computer Numeric Control. Therefore, any machine with a computer control can be referred as a CNC machine. This means, unlikely most people think, that not only the machines working with three or more axis, but any type of machine with a computer control is called a CNC machine. CNC machines used for boring and routing are called CNC point-to-point machines.

Today, the CNC machines work in nearly all branches, like metal, PVC, textile, glass, automotive etc. This can be expanded more and more. In this section, some information about different types of CNC machines used in the woodworking industry will be given. The principle of the CNC point-to-point machines will be explained in detail in order to comprehend the optimization methods discussed in Section 5 (Page 24).

Like other industries, there are various types of CNC machines doing various types of jobs in the woodworking industry. In this section, some types of CNC machines used in the woodworking industry will be given as example, and then the point-to-point type CNC machines will be concentrated on.

Automatic panel saw, complicated chair or table working, 8 axis chair working and point-to-point machines are the selected to be the examples of some types of CNC machines used in the woodworking industry.

This type of machine is used to cut panels in the desired dimensions. They are high capacity and depending on the diameter of the blade fitted on the machine, the cutting thickness can vary from 80 to 200 mm. This means, considering a chipboard mostly used in furniture industry to be 18 mm in thickness, that it makes a stock of chipboards with amount of 4 to 11 to be cut at the same time.

Those machines are normally considered to be a two axes CNC machine. One axis is the blade carriage, and other is the pusher, as shown in Figure 3.1. The blade is fixed to the carriage, and during cut, it moves up pneumatically, and moves horizontally perpendicular to the loading tables. An encoder is connected to the blade carriage so that the computer determines the position of the blade carriage. The control of position of the blade carriage is used to determine where the blade carriage should start and stop the cut where this will depend on the position of the stock of the panels on the machine, and the stock of panels' width, respectively. In other words, cut will start from where the chipboard is put, and movement of cut will continue as much as the width of the chipboard. This way, time is saved by not letting the blade to move from one end of the machine to the other end, but move only as much as the panel width. A frequency inverter controls the speed of cut so that user can adjust the speed of the motor of the blade carriage depending on the thickness of the panels.

Pusher is the device that is used to push and pull the stock of panels. When a panel or a stock of panels are loaded to the machine, the pusher moves back as much as the length of the panels. The position of pusher and it's speed, like blade carriage, is controlled by an encoder and a frequency inverter, respectively. Pusher is the most important device in panel saw machines, because this is the device that causes the machine to cut the panels in the desired dimensions in accuracy. The position of the pusher is in fact the dimension of the piece present on the machine.

There can be an automatic lifting table at the rear side of the machine for high capacity of production, as shown in Figure 3.1. In this case lifting table is considered to be the third axis and is again like pusher and blade carriage, encoder is used to locate it’s position. Since lifting table on its own is a very heavy device, the speed of its movement is normally constant, therefore its motor is not controlled with an inverter, unlike the motors of the pusher and the blade carriage. The user can determine how many panels to cut by writing total thickness of the stock of panels to be cut during the programming. Then the lifting table will move up as much as selected total panel thickness.

This type of CNC machining center is shown in Figure 3.2, and is designed specifically for routing, mortising, boring and numerous other operations on chair, table, and various other wood components. The performance of this machine stands out for operations requiring 4 or 5 axis of interpolation, and the use of a system of fixed quick sequence tools for multiple functions. Since this eliminates the need for a tool changer, cycle time is reduced and hourly output is increased. The entire machine structure has got shapes and sizes resulting from a sophisticated structural calculation. As a result of this, all deformations originating from the weight of static and dynamic masses, from displacement accelerations, and working operations, are completely eliminated. The result is an extremely high quality machine, allowing for perfectly accurate and efficient machining. The main parts of this type of machine are:

• Solidly constructed bed with sliding guides for the X axis (longitudinal traverse)
• Moving upright with vertical sliding guides (Y axis)
• Horizontal bar, carrying the machining unit, moving along the Z axis.
• Machining unit, supported by the horizontal bar, accommodating 4 motors

As a result of zero tolerance transmission, mounted on high precision bearings, the machining unit may rotate quickly and accurately on both A and C axis; the spindle heads can be positioned on 5 axis and, in accordance to the needs of the user, they can be interpolated on 4 or 5 axis. All of the four motors used by the machining unit develop their full torque of horsepower through the entire range of returns per minute (rpm). This allows the execution of any type of shaping on any of the four spindles.

All spindle heads have right and left rotation. An inverter controls the rpm between 0 and 18.000 rpm, on the basis of what it has been programmed in the CNC, according to the user's working needs. The machine is equipped with two separate tables in order to allow machining on one table, while the other is being reloaded, thereby eliminating dead times.

This is a CNC machine making three-dimensional shapes from solid wood. The picture of the machine and examples of shapes that it makes are shown in Figure 3.3.

The shapes required are in fact obtained through interpolation along the axes; work piece carriage axis and machining head axes. The use of an CNC with this type of machine has a number of advantages, the most important being:

• No need for copy templates.

Costs involved in constructing templates are weighing more and more heavily in the costs of the finished product.

• Machining precision.

The use of CNC technology eliminates the need of physical copy systems, thus avoiding friction problems as well as problems created by dust between copy bearings and templates.

• Consistent reproduction of original shape.

The memorized program is not subject to wear and allows compensation of the diameter of the tool after grinding.

• Machining of special shapes.

Extremely high production output. Due to machining speeds previously unheard of and overall production increases as a result of very short set-up times.

This is the CNC machine that is going to be concentrated in this project. Figure 3.4 shows the picture of a CNC point-to-point machine. More and detailed information will be given in the following subsections.

The CNC point-to-point machine is shown in Figure 3.4. Those machines have 3 axes, which are X, Y and Z, as shown in Figure 3.5. The axes X and Y give the coordinates where the machine head will move, and Z axis gives the depth of the hole to be bored. There also exist a forth axis in some machines that is used for the automatic tool change of the router tools. Most of the CNC point-to-point machines control the rpm of the router motors with drivers and encoders, where this does not appear to the machine operator as another machine axis.

Computer, PLC, motor driver, encoder and motor are the integrated parts that control the axes. A motor is used to move an axis. The axis is connected to the motor with a belt or with a similar system (such as, rack and pinion) so that when the motor runs, the axis begins to move. The motor driver is actually a frequency converter. Depending on the axis speed parameters stored in the machine computer, and also depending on the working speed of individual tool (drilling bit or router) programmed by the operator, the motor driver drives the motor with a suitable frequency so that the desired rpm of the motor is provided; therefore desired speed of axis is reached.

Encoder is a device that is used to give information about the position of the axes. There is a transparent disk in the encoder, and on this disk, there are black lines. The black lines are perpendicular to the tangent lines of the circumference of the disk. The number of black lines present on the disk determines the precision of the encoder. There is a sensor like device that reads these lines when the disk is turning. The number of lines on the disk gives the number of signals at one turn of the encoder, and this value is stored in the parameters of the machine program. A good precise encoder can have a value of 1500 signals per turn.

Programmable Logic Control (PLC) is used as a secondary control element in these machines. The required machine parameters are loaded to the memory of the PLC when the machine is turned on. There are small relays in PLC modules that control all electrical parts of the machine. When the user writes a program for a work piece and then runs this program for automatic execution, all information about the program, including axes speeds, is first stored to PLC. Then during the machine execution, all communications are made between machine elements (motor drivers, sensors, switches, etc.) and the PLC. This is why even if the computer of the machine is blocked, the machine keep working in automatic mode. Computer is only used to monitor the process of execution, change parametric values, write the programs for work pieces, start and end the program executions, etc.

When the motor of an axis begin to turn, the encoder connected to this motor also begins to turn (in some machines, encoders are not connected on the axis motors, but are fixed on the axes), sending signals to the PLC. This way, the PLC knows the position of the axis during its move, so that when it reaches to the desired position, the PLC instructs the motor driver to stop. In some CNC machines (like the CNC machine concerned in this project which is SCM, Tech 99 L), encoders may be connected to Computer Output of Microfilm (COM) -communication- ports of the machine computer in stead of PLC, depending on the machine model, where the computer must have as many COM ports as the number of the axes. In this case, computer of the machine will instruct PLC to stop the axis when it reaches to its position).

There exist different tool head configurations on the CNC point-to-point machines depending on the job to be done. There may be blades, routers, angular routers, etc. on the tool head. Because the topic of this project is optimization and animation of boring, only drilling bits fixed on the machines are going to be discussed. An example of drilling bit configuration is shown in Figure 3.6. This is the configuration which will be used in the optimization and animation.

The circles shown in Figure 3.6 represent the vertical drilling bits, where others represent the horizontal drilling bits. The letters “T” before the numbers stand for “Tool”. Therefore each drilling bit has a number. The user of the machine uses the tool numbers to instruct the machine with which tool the hole should be drilled. The tools are defined in the parameters, where all information for each tool such as diameter, length, maximum working length, etc. are stored in the tool parameters.

Figure 3.6 Drilling bit configuration of a CNC point-to-point machine.

The distance between each vertical drilling bit is 32 mm. This is center to center distance of the tools and is a standard for all brands and types of CNC point-to-point, and even any kind of simple boring machines.

As explained in the previous section, each drilling bit may have different length. Therefore, when the machine programmer writes a program for boring, he/she should indicate the depth of the hole to be bored. Each drilling bit shown in Figure 3.6 are fixed to a single motor, however each of them are pneumatically independent from each other. This means that each bit moves down completes the drilling and moves up independently from the others. The boring procedure works as follows:

First, the machine knows the thickness of the panel to be drilled (the panel thickness is included in the panel dimensions part of the program). The length of the bits is stored in the tool parameters of the machine. In the drilling cycle, the selected drilling bit is moved down alone pneumatically. The computer via parameters also knows the stroke of the pneumatic movement. Therefore;

[Distance between the machine table and tip of the drilling bit] MINUS [Pneumatic stroke of the drilling bit] MINUS [Panel thickness] will give the distance between the panel (work piece) surface and the tip of the drilling bit after the pneumatic stroke (after it moves down pneumatically). Then moving down the Z-axis with the required distance completes the rest. The machine now knows the distance. In order to drill the hole with the instructed depth, the Z axis has to be moved by the distance between tip of the drilling bit and panel surface PLUS depth of the hole which is programmed by the programmer. When the Z axis moves down, all the drilling bits also moves down with the selected drilling bit because they are fixed on the same head, but they do not touch to the panel since they are pneumatically up.

3.3.4 Positioning The Axes For Boring

The X and Y distance of each tool from the zero point of the machine is stored in the parameters of the machine. The zero point is the corner where the work piece is put for the operation. In other words, this is the origin of the coordinate system. The zero point and X and Y distance of each tool is shown in Figure 3.7. As indicated above, the distance between each drilling bit is 32 mm. Therefore, once the distance of one tool from the zero point is determined, then it will be easy to determine the position of other tools. Normally first tool (T1) is taken as reference distance. Below, it is shown some examples of distances of other tools.

It should be noted that “machine zero point” is also called “head reference coordinate” in the Optimization section (Section 5, page 24) of this project. As shown in Figure 3.7, T1(X) and T1(Y) are actually the X and Y offset values, respectively. Because the X and Y offset values of CNC point-to-point machine that optimization is going to made in this project is zero, then T1(X) and T1(Y) are also zero, therefore head reference coordinate gives exactly the position of Tool 1. (T1)

Figure 3.7 Zero point of the machine head.

3.4 SCM, Tech 99 L

“SCM” is the brand name and “Tech 99 L” is the model of the CNC point-to-point machine that the optimization and animation software OptTECH99 is written for. The software of the machine is Kvara®. The picture of the machine is shown in Figure 3.8.

It was indicated in the preceding subsections that there are 10 vertical and 4 horizontal drilling bits on the head of the machine Tech 99 L. The drawing of tool head configuration of this machine was viewed in Figure 3.6 (Page 16). Figure 3.9 show the tool head view of a Tech 99 L machine, with a different tool configuration from the one shown in Figure 3.6. In this tool configuration, there is number of 12 vertical drilling bits, where only 9 of them can be seen in the figure, and 3 of them are disappeared between the vertical drilling bits. In the same tool head, there is total of 3 couple of vertical holes, which make total of 6 horizontal tools. The motor for router is also marked in order to give information about complete tool configuration of a Tech 99 L model machine.

 Figure 3.10 shows the origin of the coordinate system of the machine. The picture is taken from the rear side of the machine. There seem to be two origins in the figure. In fact, this can be considered to be a secondary origin. The distance between the origin and secondary origin, in terms of X and Y values, are stored in the parameters of the machine, and when the program of a work piece is executed on the secondary origin, the machine will execute the symmetry of the program of the work. In this case, the coordinate values of the tool head will not change. In other words, the X and Y values of the head reference coordinate will not be zero when it stops on the secondary origin, like it is zero on the origin. However, the computer will make calculations in order to take the secondary origin as reference corner of the work piece. It should be noted that a secondary origin as shown in the figure is an optional, and does not present on the machine that optimization and animation software OptTECH99 was written for.