Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1989-07-11
1991-04-09
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
315151, G01J 132
Patent
active
050067010
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a sensor system for controlling machines, especially sewing machines, with a light barrier comprising a light emitter and a light receiver, the light emitter provided being an incandescent lamp supplied from an energy source, and an evaluating stage of adjustable sensitivity being connected to the light receiver.
Sensor systems of the type presently under consideration are employed, for example, in conjunction with sewing machines in order to recognize the end of seamed material during conductance of sewing operations and to automatically stop the sewing procedure or to execute a predetermined number of residual stitches following the end identification. Additional areas of application of such sensor systems are, inter alia, welding and cutting machines. The sensor system recognizes the beginning and end of the material to be worked on, based on changes of the conditions ambient in the beam path of the light barrier. This involves, for example, in case of a transmitted light barrier the more or less intense reduction in light transmitted from the emitter to the receiver based on the presence or absence of material in the beam path of the light barrier, or changes in the light transmission of the material. In case of reflected light barriers, the sensor means can respond to variations in the reflection properties during passage of the material to be worked upon. Independently of the details of the structure of the arrangement, the sensitivity of the evaluating stage connected to the light receiver is adjusted in dependence on the respective properties of the material involved in such a way that certain edge identification becomes possible; for example when sewing labels onto sewing material, an unequivocal determination can be made whether only the sewing material or the sewing material plus label lies in the beam path.
Under practical conditions, the lifetime of the incandescent lamps provided as the light transmitter is frequently unsatisfactorily brief because the incandescent lamp is under high stress not only in thermal respects but also mechanically, e.g. due to machine vibrations. The replacement of incandescent lamps by light-emitting diodes is impossible because light-emitting diodes do not afford the needed high sensitivity of the sensor system.
The invention is based on the object of providing a sensor system of the type discussed hereinabove wherein the lifetime of the incandescent lamp is prolonged and a saving in energy is obtained at the same time.
This object has been attained according to the invention by regulating the energy source of the incandescent lamp and coupling the energy source with the evaluating stage in such a way that the desired value of the regulated energy source is automatically adjustable in dependence on the sensitivity setting of the evaluating stage.
Thus, in the sensor system according to this invention, the desired value of the energy source, which latter can be designed as a controlled current or voltage source, is not maintained constant but rather is varied depending on the set sensitivity, the arrangement preferably being such that a desired value corresponding to the nominal value of the current of the incandescent lamp is applied to the controlled energy source only in a maximum sensitivity level of the evaluating stage. Consequently, the incandescent lamp is operated with its rated current only in the highest sensitivity stage. In all other cases, a lower current is applied to the incandescent lamp. As was found in voluminous tests, this ensues in a considerable lengthening of the average life expectancy of the incandescent lamp. At the same time, the energy consumption of the sensor system is thereby reduced.
In a further embodiment of the invention, the evaluating stage is associated with a first control member for a stepwise coarse adjustment of sensitivity, and with a second control member for fine adjustment of sensitivity, the desired value setting of the regulated energy source being coupled with the first control member.
The r
REFERENCES:
patent: 3917974 (1975-11-01), Lucchesi et al.
patent: 3919546 (1975-11-01), Lutus
patent: 4272188 (1981-06-01), Lehman et al.
patent: 4649267 (1987-03-01), Ray
Gekeler Manfred W.
Kothe Karl-Peter
Meier Karl-Heinz
Le Que Tan
Nelms David C.
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