Patent Application
20080173197
The present invention relates to method and apparatus for regenerating the particle-removal capabilities of a contact cleaning roller; more particularly, to method and apparatus for deciding when a contact cleaning roller should be removed from service for regenerative cleaning (renewal); and most particularly, to method and apparatus for optimizing the length of service of a contact cleaning roller between regenerative cleanings thereof.
Methods and apparatus for cleaning sheets, rollers, and web substrates by impingment of a high-tack roller are well known. See, for example, U.S. Pat. Nos. 5,611,281 and 6,196,128, the relevant disclosures of which are incorporated herein by reference. A polymer-covered roller having an electrostatically-active surface or an adhesive surface is known generally in the art as a “contact cleaning” roller (CCR). A CCR functions by having an attraction for particles that is greater than the attraction of the substrate surface along which the roller is rolled, such that particles are transferred from the substrate surface to the surface of the CCR. Over time of use, a CCR becomes progressively loaded with transferred particles and consequently becomes less effective at removing additional particles. At some point in use, it is necessary to regenerate the cleaning surface by removing and discarding the particles, as is well known in the CCR art. Typically, CCRs are provided in pairs such that a second CCR may be engaged with the substrate to continue the particle-removal process while a first clogged CCR is disengaged from the substrate and removed for renewal. For a polymer-covered roller, such renewal typically takes the form of automated washing of a clogged CCR by rotating the roller surface against a web of consumable wetted cloth material, whereby charges binding the particles to the CCR are neutralized and the particles are transferred to the cloth material. For an adhesive tape-covered roller, such renewal takes the form of removal of an outer lap of tape, exposing a fresh convolution.
A problem in the prior CCR art is knowing when to change from one roller to the other. Typically, the first and second CCRs are interchanged on a predetermined schedule. This procedure is undesirable for at least three reasons.
First, if the pre-set service period for each roller is shorter than necessary (in-service roller is still functioning satisfactorily), the roller is cleaned more often than is necessary, resulting in excess use of consumable cleaning cloth or of adhesive tape.
Second, if the pre-set service period for each roller is too long, substrate cleaning will be inferior when the in-service roller becomes clogged but still remains in service.
Third, if an unexpected episode of intense particulate contamination of the substrate is encountered by the roller, or if the distribution of particles on the substrate surface is otherwise not random, the roller may become clogged well ahead of the programmed changeover time.
What is needed in the art is a system (method and apparatus) for determining when a contact cleaning roller reaches an unacceptable level of particle loading and should be removed from service and renewed, based upon an operating characteristic of the roller itself rather than upon a set period of service.
It is a principal object of the present invention to optimize a CCR cleaning cycle and thereby to minimize the expenditure of CCR-renewal materials.
Briefly described, a CCR cleaning system for removing particles from a substrate surface comprises at least one CCR selectively contactable with the substrate surface. The CCR rolls along the surface which typically is drawn past the CCR as a continuous moving web, the CCR being rotatably mounted on a fixed axle of the system. In rolling along the substrate surface, a CCR leaves a residual (“leaving”) static charge on the substrate surface. The level of leaving static charge is sensed by a static-sensing device such as a fieldmeter in known fashion. When a CCR is first placed into service against a substrate, the leaving static charge is high. As the CCR becomes progressively loaded with particles during service, the leaving charge progressively diminishes. The decrease in leaving charge can be correlated experimentally with the particle loading of the CCR. In a first embodiment of the invention, a charge-loss action limit can be set, below which an alarm is sent, for example, to indicate that the roller should be removed from service and renewed by cleaning. In a second embodiment of the invention, the native charge on the web before contact with the contact cleaning roller (“entering charge”) is sensed by a second static-sensing device. The charge differential between the entering charge and leaving charge, which decreases with time of CCR use, is monitored and an alarm limit is set as in the first embodiment.
In a continuous-duty CCR system, first and second interchangeable CCRs are provided.
The present invention will now be described, by way of example, with reference to the accompanying drawings in which:
Referring to
In first embodiment 1, the static level on the surface of leaving portion 24 is measured by a static-measuring means S1. A signal 28 is transmitted to system control means 36, which may be a computer. At the beginning of CCR operation with a fresh CCR in place, a first static level may be measured on leaving portion 24 and stored in memory in control means 36 as a reference static level. Alternatively, a predetermined reference level may be stored in control means 36, which level may be either an average starting value for service of a renewed CCR or a threshold value for terminating service of a clogged CCR. In operation, as cleaning progresses, signal 28 is continuously monitored in control means 36.
In a first method for operating embodiment 1, a difference between the current signal amplitude and either the initial signal amplitude or the predetermined average starting value is continuously calculated. Because CCR 18 becomes progressively loaded, the current signal amplitude progressively decreases, thereby increasing the measured difference from the initial signal or the average starting value. Control means 36 is provided with an alarm limit with respect to the difference which, when reached causes control means 36 to send a control signal 42 to initiate a removal and regeneration cycle for CCR 18.
In a second method for operating embodiment 1, control means 36 is provided with an alarm limit defined by the threshold value for terminating service of a clogged CCR which, when reached, causes control means 36 to send a control signal 42 to initiate a removal and regeneration cycle for CCR 18.
Of course, control signal 42 may be simply an alarm signal that notifies an operator, lights an alarm light or audio annuciator, or otherwise makes known that an action limit has been reached. Any action prompted by control signal 42 is comprehended by the invention.
Preferably, static-measuring means S1 is a fieldmeter. However, other static-measuring means are fully comprehended by the invention, including but not limited to a static bar device (not shown) run from a DC power supply, as is known in the art of static measurement.
A typical DC static-measuring system employs a tandem set of static bars, the two bars being mechanically connected about 1″ apart. One bar emits a positive ion flow and the other bar emits a negative ion flow. A controller is incorporated into the power supply to measure the current flows to each bar. As the demand for positive or negative ion flow changes in response to changes in static charge on the moving web, a device controller sends a signal which can be used to alarm the status.
In operation, a clean CCR produces a large positive ion flow initially, generating a high static charge on the cleaned substrate, and the device output is high. A clogged CCR produces a small positive ion flow, and device output is low.
Referring now to
Referring now to
In this manner, a substrate 12 of indefinite length may be cleaned continuously of particles. Further, because CCR regeneration is carried out based on the actual degree of clogging of the CCRs, the regeneration schedule is optimized and the consumption of cleaning materials in regeneration unit 44 is minimized.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
