1. Field of the Invention
This invention relates generally to the field of measurement, and more particularly relates to a method and apparatus for measuring tape usage on standard video tape cassettes.
2. Description of the Prior Art
Recently, the use of home video recording devices has become widespread and very popular. In general, these home video systems utilize cassettes which generally comprise a plasic box containing a magnetic recording tape, with a "supply" reel and a "take-up" reel as is commonly understood in the industry. On a "blank", unused cassette, the tape is all wound onto the supply reel. As actual taping progresses, the tape is unwound from the supply reel as it passes a recording head, and then it winds around the "take-up" reel. There are two popular types of cassettes, or formats, one designated as "VHS" and the other as "BETA". From the users point ov view, the main difference between these two formats is the size and shape of the cassettes.
A typical home user will eventually encounter a situation requiring the determination of how much actual recording time remains on a cassette so that the end of a television program, for example, is not "cut off" because the cassette has reached the end of the tape before the end of the program. And, there has never been a convenient device of method of determine this.
Presently, both types of cassettes have clear plastic windows to allow the user to see the tape build-up on one or both of the reels to determine how much tape has been used already, or conversely, how much tape is still available for taping, but even after seeing the tape on the exposed reel(s), it is difficult to accurately determine how much tape has actually been used, how much is still available for further recording, how much taping time this actually represents.
Another difficulty in determining how much actual taping time remains on a cassette derives from the fact that typical video recording device can be selectively operated at more than one "speed". BETA type machines can be operated at two different speeds, and VHS machines can be operated at three different speeds. Basically, this means that the linear speed of the tape passing the recording head can be faster or slower at the user's selection. Thus, any determination of how much actual taping time is remaining on a cassette is a function of the "speed" that the machine is used at. If a higher speed is used there will be less total recording time available for any given amount of tape, as opposed to uses at a lower speed for the same amount of tape.
Other difficulties in providing such a device and method is the cost of making a device that would retain its measuring integrity after various types of abuse and/or damage.
Until this present invention, there has never been an acceptable device or method available that can inexpensively and accurately make such measurements for both types of formats, at any of the currently used speeds, and which protects and preserves the integrity of the measurements even after abuse, even partial destruction or mutilation of the device as may be encountered in use.