201: Transfer condition. Understanding parameters

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Ami Ruth Stanley
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1 Understanding parameters All CNC users will eventually have to become familiar with parameters. Though they are not even mentioned in most basic CNC courses, and though most CNC people would agree that the control of parameters is more the responsibility of a service or maintenance person than a CNC programmer, setup person, or operator, there are many parameters that affect the way CNC programs are executed. Every CNC person should, at the very least, be aware of their existence. Better yet, they should be on the constant lookout for machine behavior that is affected by parameter settings. Throughout this class, we ll be mentioning times when a parameter may be affecting the manner in which the CNC control behaves relative to a given CNC feature. Unfortunately, parameter numbers vary from one control model to another. It will be up to you to find the parameter/s in question. Generally speaking, those parameters that affect the way program functions behave will be discussed in Fanuc s Operators Manual right in the discussion of the CNC feature. For example, those parameters that are related to cutter radius compensation will be presented during the discussion of how cutter radius compensation is used. There are two basic types of parameters. Like tool offsets, all parameters are numbered. And parameters are always referred to by their numbers. With most controls, there are well over one thousand parameter functions. Parameter number 201 (below), for example, is used to determine program transfer condition. Eight bit binary type Each eight bit parameters can control up to eight individual functions. Each digit of the parameter is called a bit. Bit numbering is a little unusual, and follows binary structure. The right most bit is bit number zero and numbers ascend from right to left. The left most bit is bit number seven. (Note that bit number five is the sixth bit from the right.) The drawing shows an example. 201: Transfer condition NCR ASC SB NCR 0: The EOB code used in output is LF, CR, CR 1: LF only ASC 0: The code used for data output is ISO 1: ASCII SB2 0: The number of stop bits is one 1: two Drawing of eight bit binary parameter

2 Each bit of this parameter type will control an individual function, and contains a zero or a one. Zero is used to represent off, no, or some negative condition. One is used to represent on, yes, or some positive condition. The parameter documentation will commonly use three character abbreviations for each bit name and specify exactly what will happen if the bit is set to a one or a zero. Some of the bits of eight bit binary parameters may not be used. If there is no documentation for them in the Fanuc manual, it is probably because they are unused. In the example above, for instance, bits three through seven are unused. Changing eight bit binary parameters You must be very careful when changing eight bit binary parameters. Again, they re just a string of ones and zeros and not easy to memorize. Always begin by writing down the entire parameter (all seven bits). Then, underneath, rewrite the parameter including your change (commonly only one bit will change). With this technique, you ll always be able to set the parameter back to its original value (you ll remember its original value) should you need to. Whole number type Many parameters need to specify more than but one of two possibilities (0 or 1). They will contain actual values. One turning center parameter, for example, specifies the minimum depth of cut for the G76 threading cycle. Note that, with most controls, parameters do not allow decimal points to be included in the value for the parameter, so a fixed format must be used for decimal entries. If working with a four place fixed decimal format, for example, the value 0050 will be inch. How parameters can affect machine behavior Again, parameters affect hundreds (actually more like thousands) of things about the way a CNC machine behaves. Admittedly, many of these things are not related to machine usage (programming, setup, and operation). Here is a list of but some of the major categories of functions that parameters affect. Reader/puncher interface Axis control Coordinate system Stroke limit Feedrate Acceleration/deceleration Servo CRT/MDI/EDIT Program Pitch error compensation Spindle control Tool offset Canned cycle Rigid tapping Scaling/rotation Uni-direction positioning 2

3 Polar coordinate interpolation Index table indexing Custom macro Skip functions Graphic display Tool life management Look ahead But do note that some of these functions are related to machine usage: Coordinate system Feedrate CRT/MDI/EDIT Program Tool offset Canned cycle Rigid tapping Scaling/rotation Uni-direction positioning Polar coordinate interpolation Custom macro Graphic display Tool life management Machine tool builders strive to initially set parameters properly or at least in a way that makes their machines usable. But it is not uncommon for end users to disagree with the way certain parameters are set. A specific example With machining center controls, a parameter controls the retract amount for the G73 chipbreaking peck drilling cycle. As you know, G73 will break chips at specified peck amounts (specified by the Q word) as it drills holes. Chips are broken by the tool s slight retract from the hole. And again, this retract amount is set by a parameter. An appropriate retract should be just enough to break the chip (from to inch is acceptable). If this parameter is set to too large an amount, cycle time will suffer, since after every retract, the tool must feed back to the point that it is machining. We ve seen machine tool builders initially set this parameter to inch. If the peck drill amount (Q word in G73) is set to 0.1, this actually doubles the length of time it should take to machine a hole! This is but one of the countless times when parameter settings affect the way your machines function. Throughout this course, we ll be exposing you to more. But regardless of how many parameters we describe, you ve got to be prepared for more. Truly, any time you see a machine that is behaving in a manner that you don t like or agree with, you should consider the possibility that a parameter is affecting the function in question. The first place to look will always be in the Fanuc Operators Manual (or your control manufacturer s manual) in the section that describes the function you question. 3

4 It is not unusual for two identical machines with identical controls to behave dramatically differently due to parameter settings. Consider, for example, having two identical machining centers with identical controls that have the G73 retract parameter set differently. Say that one has the parameter appropriately set to inch. The other has the parameter set to inch. If you run the same program on both machines, and assuming you ve used G73 to machine at least some holes, one machine will take (much) longer to execute the program than the other! Importance of backing up parameters Parameters are volatile. Like CNC programs and tool offsets, they are backed up by a battery when the power is turned off. But the day will eventually come when that battery will go dead. Most controls will sound an alarm as the battery starts to deteriorate, but you must be prepared for the worst. If the machine is off for a long period of time with a failing battery (say a two week shutdown), it is possible that you will not get any warning prior to the battery failing. Any data retained by the battery (including parameters) will be lost! All current model controls allow you to back up your parameters using standard distributive numerical control (DNC) devices, using the same techniques you do for transferring CNC programs. Consult your control manufacturer s operation manual to find the procedure to back up parameters. We cannot overstress the importance of maintaining a backup copy of parameters. According to Fanuc USA, the largest single source of machine downtime is when a machine failure occurs that causes parameters to be lost, yet the CNC user has not maintained a backup copy of parameters. Much time is wasted while trial-and-error techniques are used to manually enter parameter data. BE SURE TO BACK UP YOUR PARAMETERS! Also remember to update your backup copy when you make parameter changes. As the CNC user, you - and you alone - are responsible for maintaining the backup copy of your parameters. Changing parameters As stated, most CNC people regard parameters as the responsibility of service or maintenance people. But again, there are many parameters that affect the way that CNC programs behave making them of important concern to CNC programmers, setup people, and operator. Fanuc safeguards parameters from accidental modification. That is, there is a special procedure required to change them. With older controls (like the 6TB and 6MB), an actual toggle switch (labeled pwe for parameter write enable) must be turned on in order to change parameters. This toggle switch is within the (locked) CNC control panel box. So you have to open the door (with a key), find the pwe switch and turn it on. Newer controls allow you to activate the parameter write enable function from the display screen in the SETTING mode. You ll commonly find the pwe function on the last page of the setting display. In the manual data input (MDI) mode, setting pwe to a one (1) will activate the parameter write enable function. As soon as parameter write enable is turned on, the control will go into an alarm state (alarm number 100). The only thing you ll be allowed to do with the control is change 4

5 parameters. After selecting the parameter page (from the alarm page), search to the parameter you wish to change. Type the change from the keyboard and press input and the parameter will change (as stated earlier, be sure you write down the value of any parameter before you change it especially with eight bit binary parameters). Turn off the parameter write enable function (by turning off the switch or by setting pwe on the setting page back to a zero). Finally, press the reset button to clear the alarm. 5

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