Contactless handling of objects

Details Contactless handling of objects Contactless handling of objects

2001-03-19

2003-08-05

Kramer, Dean J. (Department: 3652)

Handling: hand and hoist-line implements

Utilizing fluid pressure

By positive fluid stream directed against article

Reexamination Certificate

active

06601888

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the use of Bernoulli pickups for the contactless handling of objects. In particular, the present invention relates to the use of such devices in the field of printing and more specifically, to the handling of printing plates.
BACKGROUND OF THE INVENTION
There are many situations in which it is desirable to handle an object while eliminating or minimizing mechanical contact. This is particularly true when the physical condition of the surface of the object is a critical factor in the success or quality of an operation or product. Such situations are common in industries such as commercial printing, printed circuit board manufacture, and micro-lithography, which seek to make highly precise modifications to often delicate and mechanically sensitive surfaces.
In the printing industry, a typical example of a delicate and mechanically sensitive surface is the emulsion-coated imaging surface of a lithographic printing plate. Such plates typically comprise a substrate coated with one or more layers of radiation-sensitive material, frequently referred to as an emulsion. The coating of emulsion, particularly unexposed emulsion, is typically delicate and easily marred by mechanical contact. The marring, in turn, can produce undesirable artifacts in the final printed product. As a consequence, the printing industry is particularly concerned with methods to reduce the possibility of damage-inducing mechanical contact with the imaging surfaces of printing plates.
While damage to the imaging surface of a printing plate can occur at any point in the life of the plate, the surface is particularly vulnerable during operations requiring the movement of an individual plate from one location to another. This is especially true of imaging operations, during which an individual plate must typically be lifted from a stack of plates and then transported to or through the imaging device. This is not a trivial operation, as printing plates, though delicate, also tend to be quite large (50″×60″ is a commonly available size). Mar-free handling of plates is further complicated by the fact that the topmost and therefore most accessible surface presented by a plate or stack of plates is typically the imaging surface, making the most likely candidate for a handling surface also the least desirable one.
PRIOR ART METHODS FOR THE HANDLING OF PRINTING PLATES
In automated or semi-automated systems for handling printing plates, a number of approaches are commonly used. One main approach is to use mechanical methods to transport plates. In order to minimize the possible damage caused by mechanical handling, prior art methods of this type have relied upon mechanisms to either reduce the amount of contact with the imaging surface or to reduce the mechanical impact imposed by such contact.
Methods to reduce contact between transport mechanisms and the imaging surface include employing gravity for at least part of the transport, handling plates by the edges only, or restricting contact as much as possible to the bottom (non-imaging surface) of the plate. Such methods do not completely eliminate the possibility of damage imposed by mechanical contact with plates, as plates may be warped, bent, scratched, or dented by gripping, dropping, or conveying operations. The imaging surface is particularly vulnerable during attempts to remove an individual plate from a stack of plates, given the aforementioned problem that the most accessible surface of a stacked plate is generally an imaging surface. In such situations, not only is the uppermost plate vulnerable to damage from mechanical impact, but also the imaging surface of plate immediately below it.
Methods to reduce the mechanical impact of the gripping and transport mechanisms include padding the plate-contacting portions of the mechanisms with soft or resilient materials, as well as keeping the amount of force used to perform these operations to acceptable minimums. None of these methods, however, eliminate the risks imposed by mechanical handling, as mechanical contact with the plates must still occur.
The other main approach is to use vacuum to move and hold printing plates. This approach is employed because vacuum methods generally do not require extensive mechanical handling of objects to be moved, and because vacuum cups (also referred to as suction cups) are often made of relatively soft and resilient materials in order to enhance the seal they make with a surface. However, picking up a plate using a vacuum still requires mechanical contact in order to establish the necessary seal, and the physical impingement of a vacuum cup can be just as effective in marring an imaging surface as the impact of a careless hand or a mechanical gripper.
Ideally, methods used to lift and transport printing plates should be contactless, eliminating the requirement for mechanical contact with the printing surface. Potential methods of this type include levitation using magnetic fields, electrostatic fields, or air bearings. However, the use of magnetic forces to lift plates imposes a requirement that the plates be susceptible to electromagnetic forces. This is a requirement that is not substantially met by many plate types, particularly those that employ non-metallic substrates such as rubber or polyester. Electrostatic levitation is similarly limited, given the requirement that the plate be able to hold an electrostatic charge. Unwanted electrostatic discharges may also pose a risk to the surface of the plate. Flotation of plates on air bearings, an example of which is disclosed in U.S. Pat. No. 5,798,825, is an attractive method. However, air bearings do not address the problem of lifting a plate from a stack without causing damage to imaging surfaces.
BERNOULLI PICKUPS
Another possible method for the contactless handling of lithographic plates comes from the semiconductor industry. This method, long known in that industry, employs the well-known Bernoulli principle in order to lift and hold delicate objects such as semiconductor wafers. Pickup devices that employ this method are commonly known as Bernoulli pickups.
Bernoulli pickups are essentially pressurized fluid devices that can be used to pick up objects by creating pressure differentials between the surface of an object and a surrounding fluid medium such as air. These manipulators utilize the Bernoulli effect by forcing a fluid, typically a gaseous fluid such as air, to flow under positive pressure between the surface of the pickup device and the object to be lifted. A schematic view of a typical Bernoulli pickup, well known in the prior art, is shown in FIG.
1
. In
FIG. 1
, Bernoulli pickup
1
comprises a pickup head
3
coupled to a positive pressure pickup fluid source
5
. The pickup fluid
7
, typically a gas, flows through pickup head
3
via a shaft
9
, emerging from the pickup head
3
via an orifice
11
. When the pickup head
3
is positioned in close proximity to an object surface
13
, pickup fluid
7
is forced to flow through the space
15
between a pickup face
17
and object surface
13
. Arrows indicate the general direction of flow for pickup fluid
7
.
The flow of pickup fluid
7
out of pickup head
3
toward the outer edges of pickup face
17
creates a low-pressure region
19
(shown schematically in
FIG. 1
) between pickup device
3
and object surface
13
. This low-pressure region
19
is formed in accordance with the Bernoulli principle, as flowing pickup fluid
7
moves through space
15
at a higher velocity than the surrounding fluid medium. Region
19
within space
15
is thus at a lower pressure relative to the surrounding medium. The force resulting from this pressure differential will be normal to object surface
13
. If sufficient to overcome opposing forces (such as gravity) acting on object
21
, this force can be used to lift object
21
. in this disclosure, the force on the object resulting from the action of the Bernoulli effect will be referred to as “Bernoulli lift”.
Note that low-pressure region
19
does not

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