In magnetic recording, the recording medium, such as magnetic tape, must be maintained in intimate contact with the surface of the transducer, or "head," during the recording and playback processes. Even the smallest contaminants, such as airborne dust or smoke particles, can be of sufficient size to affect the head-to-tape spacing and to affect noticeably the overall quality of the recording and playback process, if the contaminants find their way into the region between the head and the tape. In addition, traces of the recording medium itself can adhere to the head, thereby building up a contaminant layer of sufficient thickness to cause noticeable deterioration of signal quality. Problems of contamination are especially acute in rotary head apparatus, such as videocassette recorders and camcorders. There is a need for systems to clean the head.
There are several types of known head cleaners, including those which apply solvents by various ribbons or pads, and those which use dry scrubbing materials, carried, for example, on a magnetic recording tape. The term "dry scrubbing" refers to mechanical separation of contaminants from a surface by the action of a rough surface, called the scrubbing surface, sliding in contact with the surface to be cleaned. Roughness of the scrubbing surface can be produced by such methods as attaching particulates to a substrate, providing a fabric layer as the scrubbing surface, or by mechanically embossing a pattern into the scrubbing surface. While abrasive surfaces provide dry scrubbing, it is not necessarily desirable that the dry scrubbing surface be abrasive, because an overly abrasive surface could accelerate wear of the surfaces being cleaned.
Despite the risk of accelerated wear, dry scrubbing materials which accomplish the cleaning operation without solvents have the advantage of greater safety than those which use solvents, since the use of solvents in a household environment, especially where children are present, can involve problems of toxicity, spilling, and irritating vapors.
The risk of accelerated wear due to the use of dry scrubbing materials can be reduced by limiting the abrasiveness of the dry scrubbing material itself. In U.S. Pat. No. 5,012,377, a head cleaning material which is only "mildly abrasive" is disclosed. The cleaning operation is aided by grooves in the surface of the cleaning material, which capture the contaminants removed by the abrasive material and carry them away. Presumably, the grooves may help to reduce head wear during cleaning by allowing the head to be cleaned in a shorter time, thereby limiting the exposure to abrasive materials during cleaning of the head.
Adhesives have also been used as an aid to abrasive cleaning of heads. U.S. Pat. No. 4,408,241 uses a layer having a low level of adhesion, along with a mesh layer. The mesh layer detaches contaminants from the head surface, and the adhesive layer captures them.
A second approach to reduce the risk of head abrasion during cleaning is to limit the exposure of the head to the cleaning material by providing some method for monitoring the progress of the cleaning operation while it is being performed, so that the process can be stopped when an adequate level of cleanliness has been reached. This not only reduces the risk of unnecessary head wear, but also saves the operator time by not performing the cleaning process for a longer time than is necessary. An example of this approach is U.S. Pat. No. 3,978,520, assigned to Minnesota Mining and Manufacturing Company, which achieves dry scrubbing by providing a controlled level of abrasiveness in a recordable magnetic layer. A signal which is sensitive to the cleanliness of the head is prerecorded onto the cleaning tape, so that when a video head, for example, is being cleaned, the operator can monitor the progress of the cleaning by watching the picture displayed by the video apparatus. Once the displayed picture reaches a level of quality corresponding to a clean head, the tape can be stopped and removed from the apparatus. During the cleaning operation, before the head has reached the requisite state of cleanliness, the scrubbing material contacts primarily the contaminant layer, and not the surface of the head itself.
Devices which use parameters other than the quality of the picture seen by the operator as a measure of head cleanliness also are known. U.S. Pat. No. 4,607,297 discloses a rotary head tape recording/playback apparatus having circuitry which enables head clogs to be detected. Likewise, EP 315624 discloses a system involving a tape cassette having a cleaning section, in which the dropout error rate is detected and used as a signal to initiate a cleaning step. However, these systems suffer from the limitation that they are built into the playing/recording apparatus itself, and cannot be used with an existing playing/recording apparatus not equipped with such circuitry.
A recordable head cleaning material for a computer diskette is disclosed in U.S. Pat. No. 4,516,176. Programming instructions are recorded on a diskette to enable the disk drive to perform a cleaning cycle automatically, with minimal involvement from the operator. The cleaning time is preset by programming, and there is no provision for adjusting the cleaning time based upon the cleanliness of the head.
A system for monitoring the progress of a head cleaning process in a floppy disk drive is disclosed in WO 91/02350. A cleaning step and a signal measurement level step are alternated, and comparisons are made between the signal level before the cleaning step and the signal level after the cleaning step. If the cleaning step has produced an improvement, another cleaning step is performed. This cycle is repeated until no further improvement is noted.
A cleaning tape which includes cleaning and polishing segments spliced onto prerecorded diagnostic and instructional segments is disclosed in U.S. Pat. Nos. 4,893,209 and 4,928,189. The disclosed tape does not, however, involve any interaction between the operator and the apparatus during the cleaning process, since there is no provision for monitoring the progress of the head cleaning process, or for the cleaning step to be terminated when the head is clean, since the cleaning portion of the tape is not recordable.
A diagnostic and instructional tape which enables the user to evaluate and adjust electronic functions of a video system, based upon prerecorded test patterns, is disclosed in U.S. Pat. No. 4,724,484. The test patterns disclosed are of the type commonly generated by test pattern generators used by technicians in performing electronic adjustments. While this patent suggests a variety of electronic parameters which might be adjusted or corrected, it does not mention any head cleaning operation, or using any of the test patterns as an indicator of head cleanliness.
While the head is the element of primary concern when considering the cleanliness of a tape recording system, there is also a need to consider other components which contact the tape, since it would be of little benefit to clean the head if contaminants from other parts of the system, such as the capstan and pressure roller (also called a pinch roller), were to be transported to the head region by the tape. In particular, the capstan and tape guides which control the transport of the tape past the head are known to collect contaminants.
U.S. Pat. No. 4,616,283 discloses a cassette having a tape, or "ribbon," as it is called in this patent, for cleaning the head, as well as a pad for cleaning the capstan and pinch roller in a video player/recorder. This patent also discloses a mechanically-operated shutter located in the optical path of the end-of-tape detection system for signalling the player/recorder to continue rotation of the capstan and pinch roller during cleaning. An improved version of this cleaning cassette is disclosed in U.S. Pat. No. 4,941,065. These systems can only clean the capstan if it is located at the backside of the tape.
A limitation of cleaning cassettes which depend upon mechanical brushing or wiping devices is that the design of the recording apparatus can vary widely from one manufacturer to another, and no single known cleaning cassette design can be used for all such apparatus. For example, the cleaning cassettes of U.S. Pat. Nos. 4,616,283 and 4,941,065 cannot clean the capstan if it is located on the front side of the tape. There is a need for a cleaning cassette which can be used with a variety of different apparatus, in particular a variety of different makes and models of videocassette recorders, and which is capable of cleaning not only the head, but also other components of the apparatus which contact the tape.