Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Patent
1994-06-23
1995-11-28
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
242DIG1, 318560, 360 85, 360 7802, G05F 110
Patent
active
054711240
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for sensing a position of a mechanism that controls a storage medium such as, for example, magnetic tape recorder preamble of claim 1. The method is especially applicable to magnetic tape devices for analog and/or digital recording of video and/or audio data as well as data recorders which comprise position switches. This is the case, for example, with cassette identification or loading mechanism position acknowledgement (feedback).
With a tape loading mechanism in a magnetic tape recorder having a rotating head drum (cylinder), the tape is drawn out from the cassette by means of the mechanism and wound around the head drum over an angle of approximately 180 degrees. During the eject (unloading) procedure the tape is guided back into the direction of the cassette. Various systems are known for the mechanism such as, for example, the M-loading in the case of VHS and the C-loading for Video 2000. Differing positions are required by both systems for the various operating states such as playback, pause, winding, cassette eject, etc. Each individual position represents a switching status which serves as a feedback for the controlling electronics. Here, indexing (shift) switches are mainly used, or coding switches or separate switches too. The number of feedback lines in conventional devices is about three or four, depending on the complexity of the mechanism.
In practice it has become apparent that the differences between the voltage values assigned to the individual positions are very small, whereby the evaluation becomes unreliable. Greater reliability can be achieved with very accurate resistors and a stabilized voltage at the resistor network and the reference input of the analog-to-digital converter serving for the evaluation. However, the cost of the circuit is, thereby, increased considerably. It is the object of the invention to guarantee a reliable evaluation despite the small differences between the individual determined voltage values and without needing highly accurate resistors and a stabilized voltage at the resistor network and the analog-to-digital converter. Developments of the invention are given in the subclaims.
Therefore, with the method according to the invention, highly accurate resistors or stabilized voltages are replaced by an intentionally introduced calibration procedure. Practically all deviations among the resistor values or the operating voltage are detected and neutralized through this calibration procedure in that the voltage values measured at the respective positions in the calibrating operation are stored and used as desired (target) values during normal operation. Therefore, it is not the theoretically correct desired values which are used for the comparison in the evaluation electronics but, on the contrary, those values are used as desired values which actually occur at the individual positions in practice and which are determined and stored in a calibration procedure. The resistor network can then be realized with conventional, cost-effective resistors having a greater tolerance, while no highly stable voltage is necessary as the operating voltage for the network and the analog-to-digital converter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a simplified circuit diagram for determining the position of a mechanism of a tape recorder;
FIG. 2 is a second embodiment of a circuit for determining the position of a mechanism, used for carrying out an aspect of the invention, that utilizes position switches of a resistor network such as shown in FIG. 1; and
FIG. 3 shows a numerical example for voltage values produced at different positions of the mechanism by the arrangement of FIG. 2.
In FIG. 1 the slider (wiper) contact `A'` is guided by motor M through the linkage line WV over the position transmitter (indicator) B which has three contact paths 1, 2, 3 as well as a contact path 4 clamped to ground. According to the respective position of the sliding contact `A`, the contact paths 1, 2, 4 are connected to the contact path 4. By wiring ea
REFERENCES:
patent: 4470675 (1984-09-01), Di Gianfilippo
patent: 4481551 (1984-11-01), Maeda
patent: 4821182 (1989-04-01), Leininger
Patent Abstracts of Japan, vol. 9, No. 72, 2 Apr. 1985 and Japan Pat. No. 59-203264 (*listed above).
Patent Abstracts of Japan, vol. 8, No. 82, 14 Apr. 1984 and Japan Pat. No. 58-224462 (*listed above).
Kaaden Jurgen
Reiner Gerhard
Deutsche Thomson-Brandt GmbH
Henig Sammy S.
Laks Joseph J.
Masih Karen
Shoop Jr. William M.
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