machining_center.lyx

CNC 的开放码,EMC2 V2.2.8版

#LyX 1.3 created this file. For more info see http://www.lyx.org/
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\language english
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\layout Chapter

Machining Center Overview
\layout Standard

This section gives a brief description of how a machining center is viewed
 from the input and output ends of the Interpreter.
 It is assumed the reader is already familiar with machining centers.
\layout Standard

Both the RS274/NGC
\begin_inset LatexCommand \index{RS274NGC}

\end_inset 

 input language and the output canonical machining functions have a view
 of (1) mechanical components of a machining center being controlled and
 (2) what activities of the machining center may be controlled, and what
 data is used in control.
 
\layout Standard

The view here includes some items that a given machining center may not
 have, such as a pallet shuttle.
 The RS274/NGC language and canonical machining functions may be used with
 such a machine provided that no NC program used with the controller includes
 commands intended to activate physical capabilities the machine does not
 have.
 For such a machine, it would be useful to modify the Interpreter so it
 will reject input commands and will not produce output canonical function
 calls addressed to non-existent equipment.
 
\layout Section

Mechanical Components
\layout Standard

A machining center has many mechanical components that may be controlled
 or may affect the way in which control is exercised.
 This section describes the subset of those components that interact with
 the Interpreter.
 Mechanical components that do not interact directly with the Interpreter,
 such as the jog buttons, are not described here, even if they affect control.
 
\layout Subsection

Axes
\begin_inset LatexCommand \index{axes}

\end_inset 


\layout Standard

Any machining center has one or more Axes.
 Different types of machining centers have different combinations.
 For instance, a 
\begin_inset Quotes eld
\end_inset 

4-axis milling machine
\begin_inset Quotes erd
\end_inset 

 may have XYZA or XYZB axes.
 A lathe typically has XZ axes.
 A foam-cutting machine may have XYUZ axes.
\layout Standard


\begin_inset Foot
collapsed false

\layout Standard

If the motion of mechanical components is not independent, as with hexapod
 machines, the RS274/NGC language and the canonical machining functions
 will still be usable, as long as the lower levels of control know how to
 control the actual mechanisms to produce the same relative motion of tool
 and workpiece as would be produced by independent axes.
 This is called 
\emph on 
kinematics
\emph default 
.
\end_inset 


\begin_inset Foot
collapsed false

\layout Standard

In EMC, the case of a XYYZ 
\begin_inset Quotes eld
\end_inset 

gantry
\begin_inset Quotes erd
\end_inset 

 machine with two motors for one axis is better handled by kinematics rather
 than by a second linear axis.
\end_inset 


\layout Subsubsection

Primary Linear Axes
\begin_inset LatexCommand \index{axes, primary linear}

\end_inset 


\layout Standard

The X, Y, and Z axes produce linear motion in three mutually orthogonal
 directions.
\layout Subsubsection

Secondary Linear Axes
\begin_inset LatexCommand \index{axes, secondary linear}

\end_inset 


\layout Standard

The U, V, and W axes produce linear motion in three mutually orthogonal
 directions.
 Typically, X and U are parallel, Y and V are parallel, and Z and W are
 parallel.
\layout Subsubsection

Rotational Axes
\begin_inset LatexCommand \index{axes, rotational}

\end_inset 


\layout Standard

The A, B and C axes produce angular motion (rotation).
 Typically, A rotates around a line parallel to X, B rotates around a line
 parallel to Y, and C rotates around a line parallel to Z.
\layout Subsection

Spindle
\begin_inset LatexCommand \index{spindle}

\end_inset 


\layout Standard

A machining center has a spindle which holds one cutting tool, probe, or
 other item.
 The spindle can rotate in either direction, and it can be made to rotate
 at a constant rate, which may be changed.
 Except on machines where the spindle may be moved by moving a rotational
 axis, the axis of the spindle is kept parallel to the Z-axis and is coincident
 with the Z-axis when X and Y are zero.
 The spindle can be stopped in a fixed orientation or stopped without specifying
 orientation.
 
\layout Subsection

Coolant
\begin_inset LatexCommand \index{coolant}

\end_inset 


\layout Standard

A machining center has components to provide mist coolant and/or flood coolant.
\layout Subsection

Pallet Shuttle
\begin_inset LatexCommand \index{pallet shuttle}

\end_inset 


\layout Standard

A machining center has a pallet shuttle system.
 The system has two movable pallets on which workpieces can be fixtured.
 Only one pallet at a time is in position for machining.
 
\layout Subsection

Tool Carousel
\begin_inset LatexCommand \index{tool carousel}

\end_inset 


\layout Standard

A machining center has a tool carousel with slots for tools fixed in tool
 holders.
 
\layout Subsection

Tool Changer
\begin_inset LatexCommand \index{tool changer}

\end_inset 


\layout Standard

A machining center has a mechanism for changing tools (fixed in tool holders)
 between the spindle and the tool carousel.
 
\layout Subsection

Message Display
\layout Standard

A machining center has a device that can display messages.
 
\layout Subsection

Feed
\begin_inset LatexCommand \index{feed override}

\end_inset 

 and Speed
\begin_inset LatexCommand \index{spindle speed override}

\end_inset 

 Override Switches
\begin_inset LatexCommand \label{sub:Feed-and-Speed}

\end_inset 


\layout Standard

A machining center has separate feed and speed override switches, which
 let the operator specify that the actual feed rate or spindle speed used
 in machining should be some percentage of the programmed rate.
 See Section 
\begin_inset LatexCommand \ref{sub:Feed-Interaction}

\end_inset 

.
 
\layout Subsection

Block Delete Switch
\begin_inset LatexCommand \index{optional block delete}

\end_inset 


\begin_inset LatexCommand \label{sub:Block-Delete-Switch}

\end_inset 


\layout Standard

A machining center has a block delete switch.
 See Section 
\begin_inset LatexCommand \ref{sub:Block-Delete-Switch-Interaction}

\end_inset 

.
\layout Subsection

Optional Program Stop
\begin_inset LatexCommand \index{optional program stop}

\end_inset 

 Switch
\begin_inset LatexCommand \label{sub:Optional-Program-Stop}

\end_inset 


\layout Standard

A machining center has an optional program stop switch.
 See Section 
\begin_inset LatexCommand \ref{sub:Optional-Program-Stop-Interaction}

\end_inset 

.
 
\layout Section

Control and Data Components
\layout Subsection

Linear Axes
\layout Standard

The X, Y, and Z axes form a standard right-handed coordinate system of orthogona
l linear axes.
 Positions of the three linear motion mechanisms are expressed using coordinates
 on these axes.
\layout Standard

The U, V and W axes also form a standard right-handed coordinate system.
 X and U are parallel, Y and V are parallel, and Z and W are parallel.
\layout Subsection

Rotational Axes
\layout Standard

The rotational axes are measured in degrees as wrapped linear axes in which
 the direction of positive rotation is counterclockwise when viewed from
 the positive end of the corresponding X, Y, or Z-axis.
 By 
\begin_inset Quotes eld
\end_inset 

wrapped linear axis,
\begin_inset Quotes erd
\end_inset 

 we mean one on which the angular position increases without limit (goes
 towards plus infinity) as the axis turns counterclockwise and deceases
 without limit (goes towards minus infinity) as the axis turns clockwise.
 Wrapped linear axes are used regardless of whether or not there is a mechanical
 limit on rotation.
\layout Standard

Clockwise or counterclockwise is from the point of view of the workpiece.
 If the workpiece is fastened to a turntable which turns on a rotational
 axis, a counterclockwise turn from the point of view of the workpiece is
 accomplished by turning the turntable in a direction that (for most common
 machine configurations) looks clockwise from the point of view of someone
 standing next to the machine.
\begin_inset Foot
collapsed false

\layout Standard

If the parallelism requirement is violated, the system builder will have
 to say how to distinguish clockwise from counterclockwise.
\end_inset 


\layout Subsection

Controlled Point
\begin_inset LatexCommand \label{sub:Controlled-Point}

\end_inset 


\begin_inset LatexCommand \index{controlled point}

\end_inset 


\layout Standard

The controlled point is the point whose position and rate of motion are
 controlled.
 When the tool length offset is zero (the default value), this is a point
 on the spindle axis (often called the gauge point) that is some fixed distance
 beyond the end of the spindle, usually near the end of a tool holder that
 fits into the spindle.
 The location of the controlled point can be moved out along the spindle
 axis by specifying some positive amount for the tool length offset.
 This amount is normally the length of the cutting tool in use, so that
 the controlled point is at the end of the cutting tool.
 On a lathe, tool length offsets can be specified for X and Z axes, and
 the controlled point is either at the tool tip or slightly outside it (where
 the perpendicular, axis-aligned lines touched by the 
\begin_inset Quotes eld
\end_inset 

front
\begin_inset Quotes erd
\end_inset 

 and 
\begin_inset Quotes eld
\end_inset 

side
\begin_inset Quotes erd
\end_inset 

 of the tool intersect).
\layout Subsection

Coordinated Linear Motion
\begin_inset LatexCommand \label{sub:Coordinate-Linear-Motion}

\end_inset 


\layout Standard

To drive a tool along a specified path, a machining center must often coordinate
 the motion of several axes.
 We use the term 
\begin_inset Quotes eld
\end_inset 

coordinated linear motion
\begin_inset Quotes erd
\end_inset 

 to describe the situation in which, nominally, each axis moves at constant
 speed and all axes move from their starting positions to their end positions
 at the same time.
 If only the X, Y, and Z axes (or any one or two of them) move, this produces
 motion in a straight line, hence the word 
\begin_inset Quotes eld
\end_inset 

linear
\begin_inset Quotes erd
\end_inset 

 in the term.
 In actual motions, it is often not possible to maintain constant speed
 because acceleration or deceleration is required at the beginning and/or
 end of the motion.
 It is feasible, however, to control the axes so that, at all times, each
 axis has completed the same fraction of its required motion as the other
 axes.
 This moves the tool along same path, and we also call this kind of motion
 coordinated linear motion.
\layout Standard

Coordinated linear motion can be performed either at the prevailing feed
 rate, or at traverse rate, or it may be synchronized to the spindle rotation.
 If physical limits on axis speed make the desired rate unobtainable, all
 axes are slowed to maintain the desired path.
\layout Subsection

Feed Rate
\begin_inset LatexCommand \index{feed rate}

\end_inset 


\begin_inset LatexCommand \label{sub:Feed-Rate}

\end_inset 


\layout Standard

The rate at which the controlled point or the axes move is nominally a steady
 rate which may be set by the user.
 In the Interpreter, the interpretation of the feed rate is as follows unless
 
\begin_inset Quotes eld
\end_inset 

inverse time feed
\begin_inset Quotes erd
\end_inset 

 or 
\begin_inset Quotes eld
\end_inset 

feed per revolution
\begin_inset Quotes erd
\end_inset 

 modes are being used (see Section 
\begin_inset LatexCommand \ref{sub:G93,-G94:-Set}

\end_inset 

).
\layout Enumerate

If any of XYZ are moving, F is in units per minute in the XYZ cartesian
 system, and all other axes (UVWABC) move so as to start and stop in coordinated
 fashion
\layout Enumerate

Otherwise, if any of UVW are moving, F is in units per minute in the UVW
 cartesian system, and all other axes (ABC) move so as to start and stop
 in coordinated fashion
\layout Enumerate

Otherwise, the move is pure rotary motion and the F word is in rotary units
 in the ABC 
\begin_inset Quotes eld
\end_inset 

pseudo-cartesian
\begin_inset Quotes erd
\end_inset 

 system.
\layout Subsection

Coolant
\begin_inset LatexCommand \index{coolant}

\end_inset 


\layout Standard

Flood coolant and mist coolant may each be turned on independently.
 The RS274/NGC language turns them off together (see Section 
\begin_inset LatexCommand \ref{sub:M7,-M8,-M9:}

\end_inset 

).
\layout Subsection

Dwell
\begin_inset LatexCommand \index{dwell}

\end_inset 


\layout Standard

A machining center may be commanded to dwell (i.e., keep all axes unmoving)
 for a specific amount of time.
 The most common use of dwell is to break and clear chips, so the spindle
 is usually turning during a dwell.
 Regardless of the Path Control Mode (see Section 
\begin_inset LatexCommand \ref{sub:Path-Control-Mode}

\end_inset 

) the machine will stop exactly at the end of the previous programmed move,
 as though it was in exact path mode.
\layout Subsection

Units
\begin_inset LatexCommand \index{units}

\end_inset 


\layout Standard

Units used for distances along the X, Y, and Z axes may be measured in millimete
rs or inches.
 Units for all other quantities involved in machine control cannot be changed.
 Different quantities use different specific units.
 Spindle speed is measured in revolutions per minute.
 The positions of rotational axes are measured in degrees.
 Feed rates are expressed in current length units per minute, or degrees
 per minute, or length units per spindle revolution, as described in Section