Numerical control system providing graphic machining simulation

A numerical control system in which possible interference between tools can be checked on a graphics display unit and corrected, and complex workpiece and cutting path shapes are displayed without interference. In accordance with the invention, actual tool shapes in simplified form are displayed for checking interference. Two display memories are provided so that, while one of the display memories is being used for active display, data can be written into or erased from the other. When the data entry and removal is complete, the display memories are switched over so that the time during which portions of the displayed image disappear from the screen is reduced to a negligible length. The workpiece shape is displayed as a shaded area, and any area in which a tool tip interferes is eliminated during simulated machining of the workpiece.

BACKGROUND OF THE INVENTION 
The present invention relates to an NC (Numerical Control) system, and more 
particularly to a graphics display unit for such an NC system. 
NC systems control the position of a tool with respect to a workpiece 
according to numerical information indicative of the tool position for 
machining the workpiece. Such NC systems can machine workpieces of complex 
shape easily and highly accurately and increase the rate of production. 
Graphics display units associated with the conventional NC systems display 
the current tool position, the machining path of the tool, machining 
information of the workpiece and other parts, for checking a machining 
program and monitoring machining conditions. Such a graphics display unit 
will be described with reference to FIG. 1 of the accompanying drawings. 
In FIG. 1, a tool tip mark 11 at a program original point Q.sub.0 is 
indicative of the position of a tool and can be moved by entering movement 
information to erase a currently displayed tool tip mark 11 and display a 
new tool tip mark 11 at new coordinates. The types of movement between the 
new and old coordinates can be displayed according to the line type 
(cutting feeding is indicated by the solid lines 1 and positioning by the 
dotted lines 2 in FIG. 1). As a result, paths of movement of the tool are 
displayed as shown in FIG. 1 for enabling program checking and machining 
condition monitoring. Denoted at 3 in FIG. 1 is the base line. 
The conventional graphics display unit thus constructed has suffered the 
following disadvantages: 
1) Since the tool tip mark 11 indicative of the current tool position is 
symbolically displayed, it is not possible to determine whether the tool 
tip interferes with a workpiece 10 and holder mechanisms such as a 
tailstock and a chuck (not shown). 
2) With the tool tip mark 11 moved in the foregoing manner, the tool tip 
mark 11 momentarily disappears from the graphics display unit, and appears 
to flicker while it is moving. 
3) The display of a workpiece shape and cutting paths in superposed 
relation allows determination of which portion of the workpiece shape is 
to be machined. When cutting paths become complex, they sometimes are 
displayed as being superposed on themselves, and cannot easily be 
confirmed. 
SUMMARY OF THE INVENTION 
The present invention has been made to overcome the foregoing difficulties. 
It is an object of the present invention to provide a numerical control 
system having the following features: 1) No symbolic display such as the 
tool tip mark 11 is utilized, but an actual tool shape 12a as shown in 
FIG. 2A is displayed in a simplified configuration as shown in FIG. 2B, so 
that any interference with the workpiece (FIG. 1) and the holder 
mechanisms such as the tailstock and the chuck (not shown) can be 
confirmed. 2) Two display memories are used in such a manner that while 
one of the display memories is used for display, data is written into or 
erased from the other display memory. When such data entry and removal is 
completed, the display memories are switched over, so that the time during 
which the tool tip mark or tool shape disappears can be reduced to a 
negligible length, thus providing flicker-free graphics display. 3) The 
workpiece shape is displayed as a shaded image 20 (hereinafter also 
referred to as a "plane image") 20, and any area in which the tool tip 
shape 13 of a tool shape 12b as moved interferes with such plane image is 
eliminated during simulating machining of the workpiece 10 on the graphics 
display unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will hereinafter be described in detail. 
FIG. 4 is a block diagram of an NC system according to the present 
invention. Display data issued from an NC controller 40 are stored through 
a circuit interface 52 into a memory 53 in a graphics display unit 50. The 
graphics display unit 50 has a CPU 51 for processing the displayed data, 
issuing a command to a graphics interface 54, and displaying a graphics 
pattern on a CRT 56 through display memories 55. 
A preferred embodiment of the present invention, as incorporated in a 
lathe, will be described with reference to FIG. 5. 
FIG. 5 is a flowchart of operations of the preferred embodiment of the 
invention, the flowchart including steps 1 through 3. 
Tool shape and tool movement information are entered into an input unit at 
a step 1, and a tool shape 12 is moved according to these data entered in 
the input unit at a step 2. Then, an area in which a tool tip shape 13 
interferes with a work shape is eliminated at a step 3. 
FIGS. 6A, 6B, and 6C are flowcharts of operations of moving the tool shape 
12b. FIG. 6A shows successive steps a through d, FIG. 6B respective 
processes, and FIG. 6C displayed shapes on the CRT 56. More specifically, 
the tool shape 12b is written at a new position in a display memory No. 2 
at a step 1. As shown in FIGS. 2A and 2B illustrative of a lathe tool by 
way of example, the tool shape 12b used is a simplified form converted 
from the actual tool shape 12a. As many tool shapes 12b as there are tool 
types are registered in a tool pattern file so that a desired one can be 
accessed and also displayed on the CRT 56 simply by specifying the 
identification symbol therefor. 
Then, to display a newly written graphics pattern, the display memories are 
switched over at a step b and the display memory No. 1 with no pattern 
being currently displayed is erased at a step c. Thereafter, the names of 
the display memories are changed at a step d. The above steps a through d 
are repeated to move the tool shape. 
The third step shown in FIG. 5 will be described with reference to FIGS. 7A 
and 7B. 
FIG. 7A is a diagram illustrative of simulated workpiece machining, and 
FIG. 7B is an enlarged view of a circled portion in FIG. 7A. As the tool 
tip shape 13 which is a portion of the tool shape 12b moves, there is 
created an area 14 in which the tool tip shape 13 interferes with a 
workpiece shape as displayed. Only the interference area 14 is erased from 
the workpiece shape. The interference area 14 can be specified by four 
points, a tool position P, a cutting point Q, a tool position P', and a 
cutting point Q', the latter two being taken after the tool shape has been 
moved. The cutting point Q is determined by specifying a distance to be 
cut during cutting operation. 
The steps 1 through 3 in FIG. 5 are repeated to move the tool shape 12b 
while machining the shaded image 20 on a simulated basis. 
While in the foregoing embodiment the present invention has been described 
as incorporated in a lathe, the invention is also applicable to a 
two-dimensional display in a graphics display system for a machining 
center. 
With the present invention, as described above, a tool shape and a 
workpiece shape are displayed, and an area in which the tool shape as 
moved with respect to the workpiece shape interferes with the workpiece 
shape is erased. Two display memories are employed in such a manner that 
while one of the display memories is used, data is written into and erased 
from the other display memory, and when such data storage and removal is 
completed, the display memories are switched over. Therefore, any 
interference of the tool with the workpiece and the holder mechanisms can 
be checked, and the workpiece can be machined in a simulated fashion on 
the graphics display unit. The condition of the workpiece being machined 
and its finished shape can be confirmed without having to actually machine 
the workpiece, and any display flicker can completely be eliminated during 
tool shape movement.