Abrading – Precision device or process - or with condition responsive... – Condition responsive control for sandblasting
Reexamination Certificate
1999-08-25
2002-04-30
Rachuba, M. (Department: 3724)
Abrading
Precision device or process - or with condition responsive...
Condition responsive control for sandblasting
C451S003000, C451S005000, C451S010000, C451S024000, C451S038000, C083S022000, C083S066000, C083S073000, C083S177000
Reexamination Certificate
active
06379214
ABSTRACT:
TECHNICAL FIELD
This invention relates to apparatus and methods for z-axis control and collision detection and recovery for waterjet and abrasive-jet cutting systems.
BACKGROUND OF THE INVENTION
Waterjet and abrasive-jet cutting systems are used for cutting a wide variety of materials. In a typical waterjet cutting system, a high-pressure fluid (e.g., water) flows through a cutting head having a cutting nozzle that directs a cutting jet onto a workpiece. The cutting nozzle may include a mixing tube for introducing an abrasive into the high-pressure cutting jet to form an abrasive cutting jet. The cutting nozzle may then be controllably moved across the workpiece to cut the workpiece into the desired shape. After the cutting jet (or abrasive cutting jet) passes through the workpiece, the energy of the cutting jet is dissipated and the fluid is collected in a catcher tank for disposal. Waterjet and abrasive jet cutting systems of this type are shown and described, for example, in U.S. Pat. No. 5,643,058 issued to Erichsen et al. and assigned to Flow International Corp. of Kent, Wash., which patent is incorporated herein by reference. The '058 patent corresponds to Flow International's Paser
3
abrasive cutting systems.
FIG. 1
is an isometric view of a waterjet cutting system
10
in accordance with the prior art. The waterjet cutting system
10
includes a cutting head
20
coupled to a mount assembly
30
. The mount assembly
30
is controllably driven by a control gantry
40
having a drive assembly
42
that controllably positions the cutting head
20
throughout an x-y plane that is substantially parallel to a surface
14
of a workpiece
12
. Typically, the drive assembly
42
may include a pair of ball-screw drives oriented along the x and y axes and a pair of electric drive motors. Alternately, the drive assembly
42
may include a five axis motion system. Two-axis and five-axis control gantries are commercially-available as the Bengal 4x4 cutting systems from low International of Kent, Washington.
FIG. 2
is a partial-elevational side view of the cutting head
20
and the mount assembly
30
of the waterjet cutting system
100
of FIG.
1
. The cutting head
20
includes a high-pressure fluid inlet
22
coupled to a high-pressure fluid source
50
, such as a high-pressure or ultra-high pressure pump, by a high-pressure line
23
. In this embodiment, the cutting head
20
includes a nozzle body
24
and a mixing tube
26
terminating in a jet exit port
28
. Although the term “mixing tube” is commonly used to refer to that portion of the cutting head of an abrasive jet cutting system in which abrasive is mixed with a high-pressure fluid jet to form an abrasive cutting jet, in the following discussion, “mixing tube” is used to refer to that portion of the cutting head
20
that is closest to the workpiece
12
, regardless of whether the waterjet cutting system uses an abrasive or non-abrasive cutting jet.
The mount assembly
30
includes a mounting arm
32
having a mounting aperture
34
disposed therethrough. The mounting arm
32
is coupled to a lower portion
44
of the control gantry
40
. The nozzle body
24
of the cutting head
20
is secured within the mounting aperture
34
of the mounting arm
32
.
In operation, high-pressure fluid from the high-pressure fluid source
50
enters the high-pressure fluid inlet
22
, travels through the nozzle body
24
and mixing tube
26
, and exits from the jet exit port
28
toward the workpiece
12
as a cutting jet
16
. The cutting jet
16
pierces the workpiece
12
and performs the desired cutting. Using the control gantry
40
, the cutting head
20
is traversed across the workpiece
12
in the desired direction or pattern.
To maximize the efficiency and quality of the cut, a standoff distance d (
FIG. 2
) between the jet exit port
28
of the mixing tube
26
and the surface
14
of the workpiece
12
must be carefully controlled. If the standoff distance d is to close, the mixing tube
26
can plug during piercing, causing system shutdown and possibly a damaged workpiece
12
. If the distance is too far, the quality and accuracy of the cut suffers.
The mixing tube at
26
is typically fabricated of specially formulated wear-resistant carbides to reduce wear. Particularly for abrasive cutting systems, the mixing tube
26
suffers extreme wear due to its constant contact with high velocity abrasives. Thus, mixing tubes are a relatively expensive component of the cutting head
20
. The specially formulated carbides are also quite brittle, and can easily break if the mixing tube
26
collides with an obstruction during operation of the cutting system
10
, such as fixturing or cut-out portions of the workpiece
12
which have been kicked up during the cutting operation. Accidental breakage of the mixing tube
26
increases operational costs and downtime of the cutting system
10
.
Current collision sensors use a ring sensor disposed about the mixing tube
26
which slides along or slightly above the surface
14
of the workpiece
12
. The ring sensor indicates the relative height of the workpiece. A motorized ball-screw drives the cutting head up and down to maintain the required standoff distance. When the ring collides with a kicked-up part or other obstruction, a detector detects the collision and sends a stop signal to the control gantry to stop the movement of the mixing tube in an attempt to avoid the collision.
A fundamental problem with such collision sensors is that they must have a large enough “safety buffer” between the sensor and a mixing tube to allow the control gantry enough time to stop without damaging the mixing tube. Due to the size and speed of modem cutting systems, the task of stopping the control gantry quickly to avoid a collision is quite difficult. Another problem is that any shifting of the components requires a lengthy re-calibration routine to insure proper standoff distance d. A serious collision can ruin the ring sensor.
One approach has been to simply make the ring larger the allow to control gantry more room to stop. This approach, however, prevents the cutting jet
16
from cutting near obstructions and fixtures commonly found around the edges of the workpiece
12
, thereby wasting material. Enlarging the ring also increases the occurrence of erroneous collision signals which results in unnecessary downtime of the cutting system. Finally, existing ring sensor devices are expensive and are not robust in detecting surface height or collisions when operating the control gantry at high-speed or under dirty conditions.
SUMMARY OF THE INVENTION
This invention relates to apparatus and methods for z-axis control and collision detection and recovery for waterjet and abrasive-jet cutting systems. In one aspect of the invention, an apparatus includes a linear rail, a slide member coupleable to the cutting head and slideably coupled to the linear rail, at least one actuator having a first end coupled to the slide member and a second end fixed with respect to the linear rail, a position sensor coupled to the slide member, and a controller. The actuator provides an adjustable support force that supports the weight of the cutting head, allowing the cutting head to be controllably positioned at a desired height above the workpiece. The actuator may include a pneumatic cylinder, or alternately, a linear motor.
In another aspect, an apparatus according to the invention includes a first mount member coupleable to a controllably positionable mounting surface of the waterjet cutting system, a second mount member coupleable to the cutting head and disengageably coupled to the first mount member, and a sensing circuit having a plurality of first conductive elements disposed on the first mount member and a plurality of second conductive elements disposed on the second mount member. In the event of a collision between the cutting head and an obstruction, the second mount member disengages from the first mount member to prevent breakage of the cutting head. Following the collision, the second mount mem
Chin Daniel
Kern Volker
Pesek Thomas
Sciulli Felice M.
Stewart Jonathan M.
Flow International Corporation
Seed Intellectual Property Law Group PLLC
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