Numerically controlled machine tool and method

Details Numerically controlled machine tool and method Numerically controlled machine tool and method

1995-04-27

2001-03-13

Grant, William (Department: 2121)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S056000, C318S569000

Reexamination Certificate

active

06202003

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a numerically controlled machine tool and specifically to a numerically controlled machine tool which allows a machining program to be re-executed easily after it has been stopped and which allows the machining program to be checked easily, thereby speeding up miscellaneous function processing.
2. Description of the Background Art
In recent years, machine tools using computer numerical control apparatuses with built-in computers (numerically controlled machine tools) have found widespread use in machining fields, pushing automation and labor-saving forward in these fields.
A numerically controlled machine tool consists of a computer numerical control apparatus (CNC), a power sequence circuit and a machine tool.
The power sequence circuit, which is provided between the CNC and the machine tool to do a variety of miscellaneous tasks, was ordinarily made of 200 to 300 relay circuits in the conventional art depending on a machine scale. As NC shifted from wiring logic NC to CNC, the mainstream of the power sequence circuit has changed from a relay circuit to a programmable controller (PC) using a microprocessor.
The PC is classified as either a general-purpose PC or a built-in PC dedicated to CNC. While the general-purpose PC is used with a machine tool which has several hundred tools and an auto loader and requires intricate sequences and I/O signals, the built-in PC is functional enough to be used with most machine tools.
The built-in PC for use with a lathe or a compact machining center can exhibit PC functions by utilizing the remaining capacity of a microprocessor for CNC, without an independent microprocessor being specifically prepared for the PC. In this case, the number of parts for use with the PC may be extremely small, whereby the PC achieved is excellent in both reliability and cost.
The built-in PC for use in the CNC, which can be contained in the locker of the CNC, also has an advantage that a space for installation of the PC is not required in the machine.
Data transfer between the built-in PC and the CNC is made by a common bus (or equivalent) without special drivers/receivers being required, whereby the number of I/O points required for the PC is about half that of the general-purpose PC.
Various settings (such as those of timers and counters), status display, alarm message display, etc., related to the PC can be made from the operator panel of the CNC and do not require any other operator panel.
FIG. 26
is a schematic diagram of a CNC machine tool using a CNC having a built-in PC dedicated to an NC, wherein the numeral
10
indicates a CNC and
20
denotes a machine tool. The CNC
10
consists of an NC
1
, a programmable controller (PC)
2
and an input/output circuit
3
, and the NC
1
is made up of a man-machine controller
4
controlled by a man-machine interface between an operator
110
and the CNC machine tool, a miscellaneous command controller
5
for controlling miscellaneous commands such as M, S and T commands, and an axis movement controller
6
for controlling servo axes.
The PC
2
, which stores sequence programs, is a sequence control apparatus having a structure (not shown) similar to that of a computer and consists of a CPU, a program storage device, etc., mainly semiconductor memories such as ROMs and RAMs. The I/O circuit
3
is an interface with the machine, consists of drivers and receivers, and is connected to a machine operation panel
12
, a power circuit
13
, a spindle amplifier
15
, etc., of the machine tool
20
.
The machine tool
20
has an NC operation panel
11
, which acts as the center of a man-machine interface between the operator
110
and the CNC machine tool and which generally consists of a CRT device, a ten-key pad, etc. The data of the NC
1
is displayed on the CRT device and data is entered from the ten-key pad.
The machine operation panel
12
is mainly employed by the operator
110
to manually operate the machine tool, the power circuit
13
controls the actuators, etc., of machine components
14
, the spindle amplifier
15
controls a spindle motor
16
, and a velocity control unit
17
controls a feed motor
18
.
In addition to its essential task, i.e., machining such as cutting and grinding, the machine tool has auxiliary tasks to carry out said machining, for example, workpiece loading/unloading, spindle motor start/stop, cutting oil on/off, and tool selection.
These auxiliary tasks are processed by the PC
2
in response to miscellaneous function signals (M commands), tool select signals (T commands), etc., transmitted from the NC
1
.
FIG. 27
illustrates a miscellaneous function signal interface, wherein any of two-digit BCD code signals (M
11
to M
24
) and a code reading signal (MF) are transmitted from the NC
1
to the PC
2
, this code signal is decoded by the PC
2
, required actuators are driven in a predetermined sequence, and operations commanded are performed.
When the operations are complete, a completion signal (FIN) is sent to the NC
1
. Receiving the FIN signal, the NC
1
switches off the code reading signal MF. Subsequently, the NC
1
switches the completion signal FIN off, then the M code signal off, and the processing progresses to an NC command in a next block. The timing chart of this operation is shown in FIG.
28
.
FIG. 29
is a flowchart showing a sequence of operations from the creation of a machining program to the inspection of a workpiece. While simultaneously looking at a machining drawing
100
, a programmer
101
writes an NC machining program (step
102
). The machining program is written in a general EIA format, a CNC-loaded automatic program often used recently, offline CAM or the like.
103
indicates an NC machining program written as described above.
When the creation of the machining program is complete, the machining program
103
is checked (step
104
). This check can be performed by displaying the locus of a machining path on a screen since many of recent CNCs are capable of graphic display, etc. When the machining program
103
seems to be correct, the machine tool is operated without actual machining being carried out, thereby performing a non-cutting operation in which the machining program is checked while simultaneously the operation of the machine tool is confirmed (step
105
). If cutting seems to be done without fault, trial machining is carried out actually (step
106
). If correct cutting seems to be performed, a regular cutting operation is started (step
107
) and a workpiece is inspected as required (step
108
). If a machining program fault has been found in any stage of steps
104
to
108
, the machining program
103
is corrected (step
109
), and rechecked from the required stage of steps
104
to
108
. In the stage of said steps
105
,
106
and
107
, it may be necessary for the operator
110
to temporarily stop the execution of the machining program and perform a manual operation.
For example, the operator
110
may need to remove chips caught during cutting by performing manual operation, or needs to change a tool broken midway during operation.
FIG. 30
illustrates the internal statuses of the NC
1
and the machine tool
20
at a time when the execution of the machining program has been stopped and interruption made by manual operation, etc.
Concurrently with the analysis of the NC machining program
103
(step
111
), the NC
1
outputs various commands to the machine. In response to the commands, the machine tool
20
performs predetermined operations (step
114
). At this time, status A of the NC
1
matches status A of the machine tool
20
. A status match in this case indicates that the status of the machine tool
20
recognized by the NC
1
matches the actual status of the machine tool
20
, e.g., when the NC
1
recognizes that tool No.
7
is currently fitted to the machine tool
20
, the machine tool
20
is actually fitted with tool No.
7
. Further, the position of each axis of the machine tool
20
recognized by the NC
1
matches the act

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