Adjusting the arms

After you have checked the operation of the hardware and, if necessary, corrected it using the TanBoTest program, the machine must be adjusted and calibrated. Calibration also known as setting the zero point presents no difficulty with a linear machine, but how can we adjust something that is circular and does not have a start or an end Further, several of the components of the drilling machine can be assembled in different ways for example, the drilling axis can be moved to and fro by several...

Position sensing swiches

In the machine enclosure there is an optical switch situated just between the two drive shafts for the tool arms, which operates on the reflective principle. The position of the turntable and of tool arms 1 and 2 can be determined using this switch. The sensor consists of a light-emitting diode (LED) which emits infrared light vertically upwards, and a phototransistor, also pointing upwards, which detects when a reflective object passes in front of the LED. For this reason there is a reflector...

Step Fixing the arm and

Fit the arm to the long 30 mm aluminium shaft and turn it until the 10 mm transverse hole in the shaft points in the direction of the motor spindle on the arm. The wiring will pass through this hole down into the machine enclosure. The arm is fixed to the shaft using a tapered grip, which will hold the arm absolutely rigidly to the shaft when the shaft top plate is screwed down. The last major component, the turntable, must be carefully and evenly pressed down over the centring peg found at the...

Step Building the motor drives

The two drives are built identically. They consist of a stepper motor and a gearbox, which is sealed against ingress of dirt the gearbox should not be dismantled. To connect the motor and the gearbox we use a coupling (in pack 4) which is fixed to the motor with four M3 screws and to the gearbox with two M3 screws (Figure 9). Screw the star-shaped drive fixing firmly to the output of the gearbox with four M4 screws. The now complete drive unit can be fitted from below into the machine...

Gluing the tool arm

Take the nine parts for the tool arm out of their packaging two black side pieces, a white base plate and a white top plate, and three white and two black reinforcing side pieces. As before, clean the parts with a brush. Before putting the parts together, ten M3 nuts should be fitted into the holes provided. It is easiest to put the nuts on the table and push the plastic sheet down on them. The photograph (Figure 3) shows how these are used later to attach the spindle magnet unit in the...

Step Gluing the machine

We start by gluing the white machine base plate to the three side cheeks. These parts are large and thick, so we can use them as a gentle introduction to the technique of gluing a concealed joint. All the other parts are glued in exactly the same way. After this gentle warm-up, we will be able to move on to the rather fiddlier job of gluing the drilling arms. Clear away all the drinks and greasy foods from the working area. Put away everything that is not needed for the gluing operation and...

Preparation

All the components which are to be glued together are either slotted or have milled tongues that fit into the slots. All the parts are supplied perfectly free of dirt and grease, and therefore need not be cleaned. Unnecessary handling of the areas to be joined attracts dirt and grease which make the glue much less effective. After milling a certain amount of swarf and other material may remain on some edges and corners, which must be removed. Vigorous brushing will quickly remove the unwanted...

Table Motor pulse command

1 Z Z Z D T T T Z Z Z Z Z Z Z Z Addressing bit 7, byte 1 '1'. Z (11 bits) 'Time' The time value specifies how long AFTER the execution of the motor pulse command the controller must wait before executing the next instruction. If the value is zero, then the next command (assuming it is also a motor pulse command) is executed immediately and synchronously with the present one. These three bits select the stepper motor drive stage affected by the command. The order runs from Target 1 ('000'), the...

Brawn and brains

At first glance the circuit diagram in Figure 2 may look like an impene trably complex piece of electronics, but on closer inspection we see that the brains of the circuit are actually very simple. The intelligence is concentrated in a type PIC16C64 microcontroller from Microchip, clocked at 20 MHz. This microcontroller boasts the magnificent total of 33 individually addressable I O-ports, but only 2 K of EPROM program memory and 128 bytes of internal SRAM, here used for (among other things)...

Data format

Now that we have explained how the command data are calculated in the PC and transferred over the Centronics interface to be synchronously processed by the controller, we can take a look at to the internal structure of the command data. The two bytes are concatenated to form a word. This word contains a data value, or operand, along with an address which determines how the operand is interpreted in other words, the particular command to be executed. The number of address and data bit is...

Controller functions

We have now described the main functions of the controller accepting the 16-bit wide instructions, storing them in the FIFO, and synchronously executing the commands stored in the FIFO. Of course, the calculation of trajectories is not handled by the microcontroller, since it is not designed for trigonometric calculations and would be too slow. It would also imply programming the dynamic characteristics of the system once and for all into the microcontroller. processed in the PC and then sent...

Offloading the synchronisation problem

We have therefore chosen an alternative approach to driving a stepper motor under Windows. Synchronisation is not left up to Windows software, but rather transferred to a microcontroller. The microcontroller receives a control command (for example for a motor pulse), and rather than executing it immediately, waits for further timing information to indicate when the data are to be processed. In this way, as long as the overall system is fast enough, we can obtain perfectly synchronised results...

Realtime with Windows

How can we control a stepper motor from a PC It goes without saying that we need an output drive circuit capable of supplying the current required by the motor, since none of the PC's interfaces can drive a motor directly. And then, in order to make the motor step smoothly, we need very accurate timing. At first blush it would be ideal if we could somehow connect the output stages directly to the PC and handle practically all the control signals directly as bits from the PC. The circuit would...

Gearing Mechanism

In the opinion of experts in the field there is no simple gearing mechanism that gives such a high ratio apart from a worm drive. It is mathematically impossible to achieve the ratio with two or three gears without using an unreasonably large number of teeth. At least three stages of gearing down are required with many individual arbors that must each have good quality bearings. This difficulty, and the unreasonably large amount of play in such a mechanism (and hence problems with...

Drilling under Software Control

The best thing about PCB layout programs is that they automatically generate lists of coordinates of points where holes are to be drilled. If a computer-controlled drilling machine is used, the circuit board simply needs to be fixed to the table and the machine does the rest. The only intervention required is to change drills, which can however be quite tiresome. The program must be stopped, the drilling head must be moved to a specific position, or at least raised away from the board, in order...

From Idea to Circuit Board

The individual steps in developing an electronic circuit, from the idea through to the populated prototype circuit board, usually follow on from one another more or less smoothly. First of all there is the initial design. Depending on the experience of the designer and on the complexity of the circuit, small parts of the design may first be tried out on prototyping board or by tacking components together. Then the parts are placed on a printed circuit board, leaving space for expansion, power...

Part mechanical construction

M ller (Radix GmbH) www.radixqmbh.de Now we come to the mechanical assembly of the PCB drilling machine. The components come ready-made all that is needed is a little care in fitting them together. The kit of mechanical parts for the PCB drilling machine consists of ready-drilled and machined parts that simply have to be fitted together. All the parts required to build a machine with one tool arm are included in the kit, even down to the necessary screws and glue. Not included,...

All about glue

The degree of rigidity and stability that can be obtained with a glued construction is significantly higher than can be obtained with screws. The assembly is as strong as if it were made from a single piece of material. All joints must be left to dry for at least 24 hours to ensure a rigid construction. Assembly proceeds in two stages gluing and then screwing, and should therefore take at least two days. 'Gluing' is not really the correct term here it would be nearer the mark to say that the...

Part New solutions to old problems

Elektor Electronics is proud to present an unprecedented home construction project a CNC PCB drilling machine which is economical, accurate, quick, and bristling with new ideas. Large-scale electromechanical projects have tended to be the exception rather than the rule in Elektor Electronics but these exceptions have always been well received. Many readers will have fond memories of the Plotter and Plotter Mark 2 projects, which hundreds of constructors across Europe have built and which even...

Table Drilling command

0 T T T 1 1 B B B B B D D D D D Addressing bit 7, byte 1 '0' bits 2 and 3, byte 1 '11'. T (3 bits) 'Target' These three bits select the output stage for the drilling command. The machine can be fitted with up to four arms, and each of these arms has its own drill and a dedicated driver stage on the controller board. The targets are numbered from left to right, starting with Target 1 ('000') at connector K10, where the solenoid for the first arm is connected. The corresponding drill motor is...

Step Fitting the mechanical parts to

Take the pack containing the four cone bearings and the two packs labelled 'Mechanik 1' and 'Mechanik 2' out of the packaging. These comprise a complete set of mechanical parts for one axle (Figure 5). The cone bearings consist of two separate parts, an outer race and an interior part with the rollers. The bearings are rather oily this oil should be cleaned away except on the race and on the inner part, so that only the moving parts are lubricated. Push two of the races into the holes in the...

Boring Story

Next, holes are bored in the circuit board using drills of various diameters. In general, three drills are used the commonest is 0.7 mm or 0.8 mm, used for almost all small components such as resistors, capacitors, ICs it is even suitable for the leads of some electrolytic capacitors. A 0.9 mm or 1 mm drill is used for most connectors, square pins and the larger diodes. Larger connectors, solder pins and similar components require a 1.2 mm or 1.5 mm drill. Usually a mini-drill is used in a...

The strobeedge trick

How can the controller know which of the bytes is the first and which the second Counting is one option, but not a very reliable one a single transmission error and all successive commands will be wrongly interpreted. The error must be detected and the controller reset. Alternatively, the data bytes could include further information to allow the controller to identify which is which. However, this also has its disadvantages. The marker bits naturally reduce the amount of real information...

Using the Centronics interface

Communication with the controller could be carried out over any PC interface. The Centronics and V24 (serial) interfaces are always available, and are particularly suitable candidates. There are certain problems associated with the V24 interface getting the wiring right and arranging handshaking can be full of pitfalls. Matters are also more complicated for the microcontroller, which must first convert the serial bit stream into parallel bytes. And, if the microcontroller does not contain a...

PCB drilling machine

After discussions with several readers during the HobbyTronic Fair in Dortmund, Germany, and several e-mail enquiries and telephone calls, we have decided to describe briefly once more the operation of the PCB drilling machine, along with its advantages and capabilities. Basic features of the PCB drilling machine Our project is a CNC machine which carries out operating commands calculated with the help of a computer. Conventional CNC machines are constructed using linear components, such as...

The drive system how it works

Drilling Machine Drive Unit

When we started looking for a simple design for the drive system to give precisely the high gearing ratio required for our machine, we were met by shaking heads the experts told us that high ratios could only be obtained by using multiple separate stages, each with a small ratio, multiplying together to give the total desired. Using an ordinary planetary drive a practically-realisable gearing stage with a ratio of up to about 7 1 can be built. This is due to the fact that multiple spur wheels...

The first test

The TanBoDrive driver software requires that the drilling machine be fully functional, both electrically and mechanically. The input data in this case drilling data in Excellon format are specially processed and transformed into the required commands, in the form of motion commands and drilling commands, to be sent to the microcontroller. More than this TanBoDrive cannot do. Linear interpolation, as required for interpreting HPGL-format files, is included otherwise the machine could not even...

Polar Coordinates

Here a point on a surface has its position defined not by X- and Y-coordinates as in the Cartesian system, but by a length distance from a fixed point and an angle. Polar and Cartesian coordinates can be inter-converted without loss of information. In the PCB layout, draw a circular pad with diameter exactly 3 mm in an unused area alternatively, use a mounting hole. In the circuit board itself, before exposure, drill a hole with diameter 3.1 mm, in the corresponding place to the pad on the...

Drilling Machine

M ller Radix GmbH www.radixgmbh.de In this final part on the construction of the PCB drilling machine, all its functions are tested and the machine is calibrated. The machine is then ready for its first job. By the time you read this, the first PCB drilling machines have already been delivered and perhaps also assembled. It is therefore high time that our description of the machine be completed. All that remains is the calibration of the machine. The machine must be calibrated...

Part PCB construction

Pcb Construction

M ller Radix GmbH www.radixqmbh.de The controller board contains all the electronics for the plate motor and four drill arms. As a matter of course, the board population is in accordance with the actual number of drill arms you have in use. All the components of the circuit can be built onto a single-sided printed circuit board. The PCB and component layout are shown in Figure 1. The power supply as far as the transformers is also built onto the circuit board it provides a 30 V...

Step Building the drill lift unit

We now turn to the Z-axis drive, i.e. the lift unit for the drill. All the required components are in pack 5. First the drill motor is fixed to the longer of the two black plastic plates from the shaft side using two M3 screws. On the motor side the two long pillars are fixed to the plastic plate with M3 screws. The second black plastic plate is fitted over the motor housing from behind the motor and fixed firmly using the pillars. The two precision machined hardened steel shafts are fitted...

Cartesian coordinates a heresy

Drilling Machine Mechanism

Has anyone every seriously wondered why CNC machines always work using the Cartesian coordinate system Why are X-, Y- and Z-axes always used Why, when such machines are so difficult to build The linear guides must be absolutely parallel, because otherwise the carriage will jam. The axes must be at exactly 90 degrees to one another, or else everything goes askew. The table must be absolutely true and the whole machine must be solidly fixed to a base. These are all disadvantages. But the greatest...