Читать книгу CNC Control Setup for Milling and Turning: - Peter Smid - Страница 12
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The control system is the heart and brain of all CNC machines - it is their main component. In fact, this whole handbook is about the control system of a CNC machine. The abbreviation ‘CNC’ stands for Computer Numerical Control, and is commonly referred to as the control or the control system or the control unit and the even more common expression - CNC Control, in short. Although the expression CNC control does not follow any exact rules of the English language because of literal redundancy (Computer Numerical Control control), it is still a commonly accepted form of expression, at least in informal communications, in some cases including this publication.
Regardless of any specific description applied, the control system of any CNC machine can be a complex entity and often intimidating for new users. There are many aspects to the control system that are used by skilled professionals in different fields. For example, an electronic expert will look for different features of the system than a mechanical expert. Features relating to the CNC programmers and CNC operators will share many features, but each area of interest will always be unique. From a more practical perspective, both CNC operators and CNC programmers look only for those control features that are required in their respective fields.
Looking at a CNC machine (mill, lathe or other), the control system is identified by its visual components, in the form of a large panel, where its most noticeable features are the display screen and a keyboard or a keypad. Various switches, buttons, lights, etc., are also part of the control system. A short summary lists the most important visual features of any control system:
▪Display screen (monitor) with soft keys
▪Power ON/Off switches
▪Keyboard
▪Handle
▪Push buttons - Toggle switches - Rotary switches
▪Confirmation lights
▪Alarms and Errors
▪... any several others
Each of these features is covered in this handbook in sufficient detail. While the overall control system panel may include many overwhelming features (particularly for a beginner), it is easier to understand individual parts by a simple separation into two distinct sections:
▪Control Panel
▪Operation Panel
To make such distinction or such separation, it is important to know some background of CNC machine manufacturing.
CNC machine tools are manufactured by companies that have expertise in building machine tools. Without suggesting any preferences and their origin, well known companies that manufacture CNC machining centers and have a large presence in North America are OKK®, Mori-Seiki®, Matsuura®, Makino®, Haas®, Fadal®, Mitsubishi®, Kitamura®, Okuma®, and others. European and Asian markets will be different in the brand names, but these sample names represent machine tool manufacturers regardless of the actual machine origin.
Except for some rare exceptions (Haas, Fadal, Fagor, etc.), most machine tool builders do not manufacture their own control system (the computer part of the machine) - they concentrate at what they do best, which is building machine tools. On the other hand, each CNC machine tool requires a CNC control system.
Just as there are CNC machine tool manufacturers that do not make their own controls, there are CNC control system manufacturers that do not make their own machine tools (except some minor exceptions). The reasoning is quite simple - ‘we know what we’re good at and specialize in doing it’.
Those machine tool manufacturers that make no control systems of their own do only one thing - they purchase the control system that supports their machines.
That also means there is a field of manufacturing that specializes in design and manufacturing of the computer portion of the CNC machine only - the actual control manufacturer. Names such as Fanuc®, Yasnac®, Mitsubishi®, Siemens®, Heidenhain®, and many others are all part of this large field.
Let’s sort all this out.
As stated earlier, any control system of a CNC machine can be identified by its two main components:
▪Control Panel
▪Operation Panel
For both operators and programmers, these two control system features form the main area of interest.
Control panel represents the computer part of the CNC machine operations. It is mainly used to make changes in the software part of the system whether in the part program itself or in various software settings, such as offsets and parameters.
Operation Panel represents the hardware part of the CNC machine operations. It is mainly used to change various settings and modes, overrides, and allows manual motions of the machine axes.
The distinction of software/hardware as separate entities is rather simplistic, as both are always connected. At the same time the distinction helps to illustrate the many functions offered by any CNC system.
Every CNC system provides a physical area where a number of part programs can be stored for a period of time. This area is called the system memory.
A program that exceeds the memory capacity cannot be loaded to or run from CNC memory. Even a large memory capacity is always limited, but can be increased by hardware updates. For a CNC operator, it is important to know how much memory is remaining before loading a program. Ideally, all memory capacity should be measured in characters of text, both used and remaining.
The latest controls system DO show memory capacity in characters
Unfortunately, many older controls do not have this facility and use one of two other methods:
▪Memory available as number of pages
▪Memory available as meters or feet
In the first case, the number of pages refers to the number of full screen displays of the program. This is a rather hard way to establish the capacity remaining, and requires some practice. The method of measuring memory capacity in meters or feet seems a bit strange at first, until you understand what meters and feet refer to.
Yes, they refer to the equivalent length of paper tape that used to be the original source of program data in the early stages of numerical control. Although NC or CNC machines using a paper tape today are rather rare, the method of memory capacity measurement has prevailed.
Most current CNC programmers and CNC operators are not familiar with paper tape as the data source and probably have never even seen one. The one reason that the paper tape is even mentioned in a modern handbook such as this is not nostalgia. The reason for its inclusion is the fact that there are still remnants of tape references used on even the most modern CNC systems.
Paper tape was a one inch wide tape, made of special paper (or other material) to exact specifications. Across the tape was a set of odd or even number of holes, punched in different configurations, where each set of holes represented a single character, according to EIA or ISO standard. The separation of one set of punched holes from the next was exactly 0.1000 inches (2.54 mm). This dimension - this 0.1000 inches - is the key to understand memory capacity of a control system, identified in feet or meters.
Keep in mind that this standard has been used around the world, although the base unit was an inch - after all, numerical control technology originated in the United States, where imperial measurements have been predominant (although that is now changing as well). Also keep in mind that most current controls are of either Japanese or German origin, two countries where metric system has been standard for centuries.
The following two tables provide conversions of several common memory capacities, as installed in the control system - the first one converts meters to feet:
The second table converts feet to meters:
As you may expect, it is impossible to list all possible options, but a simple calculation or two will provide the answers required.
First, some conversions of various units, in case they are necessary for additional calculations:
| 1 inch | = | 25.4 mm |
| = | 0.0254 m | |
| 1 foot | = | (25.4 × 12 inches) / 1000 |
| = | 0.3048 m | |
| 1 mm | = | 1 inch / 25.4 |
| = | 0.039370 inches | |
| 1 m | = | 1000 mm / 25.4 |
| = | 39.370079 inches | |
| 1 foot | = | 12 inches / 39.370079 |
| = | 0.3048 m | |
| 1 meter | = | 1000 mm / 25.4 / 12 |
| = | 3.28084 feet |
Conversion of METERS to FEET:
Meters are the units of input to be converted into equivalent number of feet:
| Feet | = | Meters / 0.3048 |
Conversion of FEET to METERS:
Feet are the units of input to be converted into equivalent number of meters:
| Meters | = | Feet × 0.3048 |
Conversion of METERS to CHARACTERS:
Meters are the units of input to be converted into equivalent number of characters:
| Characters | = | (Meters × 1000) / 2.54 |
... or ...
| Characters | = | Meters / 0.00254 |
Conversion of FEET to CHARACTERS:
Feet are the units of input to be converted into equivalent number of characters:
| Characters | = | Feet × 120 |
Conversion of CHARACTERS to METERS:
Characters are the units of input to be converted into equivalent number of meters:
| Meters | = | Characters × 0.00254 |
... or ...
| Meters | = | (Characters × 2.54) / 1000 |
Conversion of CHARACTERS to FEET:
Characters are the units of input to be converted into equivalent number of feet:
| Feet | = | Characters /120 |
Program files are always stored as pure text files on computers, in standard ASCII format - that means no formatting is involved - no underlines, no italics, no bold characters, etc. ASCII is an acronym that means American Standard Code for Information Interchange.
When a pure text file is stored, the computer operating system such as Windows™, indicates the number of bytes the file occupies on the hard drive (or disk). Although not exact, this file size can be used as a guide -typically, the number of bytes exceeds the number of characters. For example, a text file that shows 3500 bytes may have only 3000 characters, spaces included. Fanuc controls do not consider spaces as characters -spaces are ignored.
DNC Alternative
Although CNC memory capacity can be expanded by adding more memory chips or boards, an inexpensive alternative is the use a of remote computer that serves as a DNC source unit.
DNC stands for Direct Numerical Control or Distributed Numerical Control. Although there is a certain overlap in using these two terms, direct usually means one Personal Computer to one CNC, whereby distributed usually means one Personal Computer to several CNCs. In both cases, suitable software and cabling is required.
The illustration below shows a typical control panel for a CNC machining center. Turning center control panel will be almost identical. The letter -M in the model identification stands for Milling - a CNC turning center (lathe) will have the letter -T instead (for Turning).
Although the control panel layout and its features will vary from one manufacturer to another and even from one control model to another for the same manufacturer, there are enough similarities to group them and examine each group.
The control system has its own independent power source, therefore it has its own ON-OFF buttons. Even if the CNC machine itself is turned on, it does not mean its control system is under power as well. However, the machine power has to be turned on before the control system can be turned on via Control Panel. The main reason is to separate mechanical, pneumatic and hydraulic elements from the electronic elements.
The OFF button of the Control Panel is usually the first one to use when the machine is powered down. Usually, the Power-Off order is the opposite of the Power-On order. As the exact procedures will vary from machine to machine, always consult the manufacturer’s recommendations and procedures.
The largest area of the Control Panel is the display screen - the monitor of the whole control system.
There are three main elements:
▪Display area
▪Arrow soft keys
▪Selection soft keys
When the power is supplied to the control panel, the display shows its default screen. In order to navigate between many screen pages, the control system offers several soft keys, located just below the display screen (five keys shown in the illustration + two for navigation).
In order to avoid hundreds of buttons and a very large control panel, modern control systems only display features directly related to some main selection group. For example, if you choose the POS selection key, the screen will show only those features that are related to various positions - such as absolute, relative, machine, distance-to-go, etc.
Soft keys always work in conjunction with Selection Keys (described next). The illustration shows the meaning of soft keys when the Offset/Setting selection key is pressed.
Incidently, the meaning of the word soft-key is not related to its physical composition or the feel of one’s finger when the key is pressed. The word ‘soft’ is just a short form of ‘software’ - as in ‘software keys’. The implication is that it is the software of the control system that determines the meaning of each soft key, based on the selection key. That is the main reason why the soft keys are not identified in any way.
Navigation Keys
Regardless of the number of actual soft keys, there are also two arrow keys - one to the left and one to the right of the actual soft keys:
| ▪LEFT arrow key | ... Function Menu selection |
| ▪RIGHT arrow key | ... Operation Menu selection |
In conjunction with each other, these two arrow keys are used to navigate different pages and sub pages of the screen display.
As mentioned in the previous section, the actual functionality of each soft-key is always directly dependent on the currently active Selection Key. In other words, the selection shown on the screen above each soft key will be different for each selection key. The illustration below shows the most common key selections available:
POS Key
POS indicates settings related to various position displays. This is probably the most commonly screen used in part setup. The main modes that can be used are:
| ▪ABS | ... Absolute display |
| ▪REL | ... Relative display |
| ▪ALL | ... All displays |
| ▪MACH | ... Machine position display |
The two main displays - ABS and REL - are used the most. The absolute display is normally used during program processing - it shows the current tool position based on part zero location. The relative display is used mainly during setup, for activities such as setting work offset, tool length offset, and others. In this case, at a certain critical position (commonly at machine zero), the CNC operator sets the relative display to zero and makes the required offset measurement, for example, sets G54 work offset or G43 H.. tool length offset.
Both ABS and REL displays are usually shown in larger form than normally, so they can be seen from a distance during part setup.
MACH selection key shows the current tool position always measured from the machine zero (home position). This display is totally independent from any offset setting or part program data.
If you want to see both ABS and REL position displays, and MACH display as well, on the same screen, just press the ALL selection key. The display of each part is smaller, but all important data is shown on a single screen. In addition to the four modes, the control system also shows some current activities from the part program, such as current spindle speed, cutting feedrate, active program codes, etc.
PROG Key
PROG indicates the program mode. The contents of the screen - what you can actually do - depends on the selection of control mode, located on the operation panel of the control (described in the next chapter):
For the PROG key selection to work, either the MEM (memory) or the EDIT mode has to be selected.
In MEM mode, the currently loaded program can be monitored by viewing it on the screen. Current and next block can also be viewed. No program changes are possible in MEM mode.
If you want to make changes to the current program, you have to choose the EDIT mode from the Operation Panel. As these two modes are separate, there is no possibility of making a mistake, for example, by editing part program currently active.
In the EDIT mode, program can be edited, viewed on the directory screen, program can also be loaded into memory or deleted from the control memory.
Many controls even offer a feature called background edit, which allows programming of the next job, while the current job is running.
OFFSET / SETTING Key
Contrary to some beliefs, this is a dual function key -it does not mean Offset Settings - it means Offset and Settings !
Tool length and cutter radius offset can be set by selecting the OFFSET soft key. Work offset is set by selecting the WORK soft key. In order for either setting to work, the OFFSET / SETTINGS key has to be pressed first.
In this mode, various settings may also be done at the control. The most common setting is the selection of units - metric or imperial (mm or inches). Another setting may relate to mirror image and macros - several others are also available from this screen. Although these settings can be done at the machine, it is always important to follow this recommendation:
Settings that can be done at the control AND in the program, should always be covered by the program
SYSTEM Key
SYSTEM selection key is the entry into the inner workings of the CNC system. There is no harm looking at this display but making any changes is not part of general operator’s duties. Under the SYSTEM key selection, you will find Parameters Setting Screen, Diagnosis Screen, PMC Screen (PMC stands for Programmable Machine Control, which is a version of PLC - Programmable Logical Control). PMC/PLC is used by machine tool manufacturers for many different applications. One of the more common ones is connecting various devices together. For example, a transfer system between two CNC machines uses PMC/PLC, The same applies internally for almost all mechanical functions.
SYSTEM selection key should only be used for viewing various data - changes should always be left to qualified technicians
MESSAGE Key
Typical screens that appear in the Message mode relate to various alarms and operation. They may also show alarm history. Message screen will also appear when a macro program includes message to the operator via a part program.
GRAPH Key
An option on many controls - if available, it shows toolpath motions graphically. The main benefit of this optional feature is that a program can be graphically tested prior to actual machining.
CUSTOM Key
In the majority of CNC applications, the Custom selection key is used by the machine tool manufacturers for some unique activities of their CNC machine. For example, by pressing the Custom key, you may find procedures related to automatic tool and pallet changers,
In CNC programming, the word address refers to any letter used in the part program. For example, rapid motion G00 uses the G-address, tool change command M06 uses the M-address, and spindle speed S1200 (r/min) uses the S-address. These are just some of many addresses that are used in a typical part program.
The control panel keyboard is not just an exclusive address oriented keyboard, as it also includes digits and special symbols. In reality, the control system keyboard is a multifunctional alpha-numerical keyboard, which is actually a description used by some control systems.
Note that the keys containing letters also contain secondary characters. Grouping of the letters is designed to be convenient for CNC program data entry, and does not follow the common QWERTY keyboard layout.
Secondary characters are accessible via the Shift key. Not all secondary characters may be available, even if they appear on the keyboard. A pair of parentheses ( ) is used for inclusion of comments into the program, while square brackets [ ] are used only in macros. Macros also use the # symbol, equal sign =, asterisk * for multiplication, plus sign + for addition. From the numeric pad, macros also use subtraction sign - and forward slash / for divisions. Question mark ?, comma ‘,’, ampersand @, and the ‘at’ symbol ‘&’ are not normally used in part programs. SP is a symbol for ‘space’ to separate words.
As described already, the shift key is used the same way on the control panel as it is used on standard computer keyboard - it selects the secondary character, if available.
Numeric section of the keyboard contains only primary keys - no shift is required - it covers all digits from 0 to 9 as well as the negative sign and the decimal point. There is also a symbol for the forward slash, used as a block skip symbol in CNC programming.
There are three Edit keys on the control panel. They are used to edit programs stored in the CNC memory:
| ▪Alter | ... changes existing program entry |
| ▪Insert | ... adds a new entry into an existing program |
| ▪Delete | ... removes program entry |
Both Page and Cursor keys are navigational keys. They narrow down the available screen selections:
Page refers to a single display of the control screen. For example, a long program may not fit on a single screen and can be viewed only by scrolling from one page to the next, in ascending or descending order. Each time the Page key is pressed, another display screen will appear. Page-Up and Page-Down arrows select the direction of the page scrolling.
Cursor is normally used on the selected page. Its main purpose is to narrow down the selection within a page. Vertical cursor arrows are used to select a particular line displayed on the screen, while horizontal cursor arrows are use to select a particular item with the selected line.
EOB or E-O-B is just a short form for the End-Of-Block character. When entering a part program into the control system in Edit or MDI mode, each program block has to be separated from the next program block. End-Of-Block key is used for that purpose.
CAN is the Cancel key. As the name suggests, this key is used to cancel an erroneous data entry.
INPUT is a special key used for data settings. Unlike the INSERT key, it is not used for program data. Its main use is to set various offsets, settings, parameters, etc.
Do not confuse INPUT with INSERT
INPUT is used for data settings INSERT is used to add program data
Pressing the RESET key, many default conditions are restored. One of the most common use of this key is to cancel alarm or error condition.
Keep in mind that the actual cause of any alarm has to be addressed first, and the problem resolved before the Reset key can become functional.
The HELP key is quite self-explanatory - it provides details relating to various commands - commonly used in MDI mode. Various alarm details, as well as details relating to operation methods and parameter table can be found here.
The control system and its display/keyboard portion is closely connected to the operational features of the CNC machine, the Operation Panel. The next chapter will cover this subject in detail.
