GB2308137A - Method for monitoring the detection conditions for controlling a yarn storage feeder - Google Patents

Description

Title: Method for surveying the detection conditions for controlling a yarn feeding device DEscRIPTION The invention relates to a method according to the preamble part of claim 1, as well as a yarn feeding device according to the preamble part of claim 7.

According to a method as known from US 48 65 085 (corresponding to EP-0199059 B1) of this kind the sensor device operates with a first receiver surveying the axial movement of yarn windings on a stationary storing drum, and a second receiver surveilling exclusively the quality of the light transmission. An exitsignal of the second receiver becomes compared with a threshold value in order to gain an additional signal. With the help of this additional signal, the light intensity for both receivers is increased corresponding with a deterioration of the light transmission. Also, an alarm signal for an operator can be generated indicating the need of cleaning the light transmission path by removing contamination disturbing the light transmission.

According to a method as known from US-A-49 63 757 a light source supplies two receivers, one of which exclusively senses the motions of a yarn, the other of which exclusively detects the light transmission equality, in order to maintain the relation between both exit signals of both receivers substantially constant and to compensate for a deterioration of the light transmission guality.

According to a method as known from US-A-39 07 440 phase-offset light pulses for only one receiver are generated by means of two pulsed light sources, only one receiver sensing with the light pulses of one of the light sources a yarn motion. The exit signals originating from the light pulses not used for the detection of the yarn are compared with a nominal signal value in order to maintain a predetermined relation between both signals and to compensate for disturbing influences.

A nethod is known from We95/16628 for controlling the drive motor of a yarn feeding device for a knitting machine. Said yarn feeding device comprises a rotatably driven storing drum, and a stationary sensor device. Circumferentially offset surface areas on the storing surface are simultaneously optoelectronically sensed by means of a plurality of sensors. In case that the yarn is present in the detection-zone, all of the sensors simultaneously generate equal exit-signals. In case of absence of yarn in the detection-zone the sensors to the contrary simultaneously generate different exit signals. By discrimination of the exit signals control signals are derived.

The drive motor is driven as long as the detection zone is free from yarn and unless the yarn again reaches the detection zone.

When replenishing the yarn store on the storing surface, i.e., with driven drive motor, a speed signal for a control circuitry is derived from the exit signal of one of the sensors. A predetermined quality of the light transmission is required for the operation of the sensor device. Contamination and lint, unavoidably occurring when processing yarns, tend to deteriorate the quality of the light transmission with increasing duration of operation. The sensor device then fails. The storing surface becomes empty. This might lead to a fault in the product produced in the textile machine being supplied with yarn by the yarn feeding device. Therefore, it is customary, that an operator cleans the light transmission path within periods based upon experience, e.g. by pressurised air or by sweeping.However, said cleaning steps then are carried out more often than necessary, or a disturbance occurs due to a lack of care of the operator.

It is a task of the invention to create a method of the kind as disclosed above, as well as a yarn feeding device, allowing in a structurally simple way and with simple circuitry-technique to reliably find out and indicate such a deterioration of the detection-conditions which just barely allows a correct operation of the sensor device and which can be removed without damage in the product produced by the textile machine supplied with yarn by the yarn feeding device Said task can be achieved according to the invention with the features of claim 1 and the features of claim 7.

According to the method, the object-exit-signal generated for control purposes is also used to check the quality of the detection conditions, e.g. the quality of the light transmission at the sensor device. This does not need appreciably additional components at the sensor device, or at the storing surface. The decisive detection conditions necessary for the function of the sensor device become examined, e.g. the light transmission quality in the detectionzone, i.e. exactly at a location, where the quality is decisive for the function of the sensor device for controlling, e.g. the drive motor, and not at a location which is distant from the detection zone. The signal level of the exit signal and also of the test signal are changed by a deterioration of the detection condition.The signal level of the test signal then is compared with a threshold value set for a just barely acceptable deterioration of the detection conditions. Finally, the signal level of the test signal falls below said threshold value. This leads to the alarm signal. By means of the alarm signal an operator becomes alarmed just in time, i.e. neither too early nor too late, to clean the operating area of the sensor device, i.e. for example the light transmitting path.

However, the alarm signal suitably also can be used to automatically activate a cleaning device for the sensor device which cleaning device automatically carries out a cleaning step, e.g. by blowing away or sweeping away contamination.

In the yarn feeding device an examination of the detection conditions is made exactly at the location at which the object is detected, i.e. at a location where the quality of the detection condition is of decisive importance for a correct function of the sensor device. Since the object-exit-signal itself, in addition, is used as a basis for the test signal, no additional sensor components or auxiliary means are needed at the storing surface. components, already used for the detection of the object, also are used for the test-routine.

The detection conditions are checked during such operation periods only, and the alarm signal is generated in order to alert the operating personnel to remove the disturbance, during which operation periods the deterioration of the detection condition might disturb the operation of the sensor device.

The examination is not carried out during unimportant time periods, in which the detection condition is of no influence on the operation of the sensor device. The structural features provided are advantageous, with yarn feeding devices, having a storing surface driven by the drive motor rotatably driven storing body) as well as with yarn feeding devices having a stationary storing surface (stationary storing drum and rotatably driven winding-on-element), in order to reliably determine at each such device when a disturbance has to be eliminated.

With the variant of the method according to claim 2, a simple logical evaluation of the occurrence or the non-occurrence of both signals is carried out in order to generate the alarm signal at a correct point in time and on the basis of a correctly determined detecting condition.

According to a method variant as mentioned in claim 3, the test signal, as well as the speed signal for control purposes of the drive motor, are formed out of the object-exit-signal. An examination of the detection conditions is only carried out in case the drive motor must be driven, and when there is danger of emptying the storing surface. Although the alarm signal is generated when the test signal fails to appear, the speed signal still appears for unobstructed use.

with the method variant according to claim 4, comparison of the signals is reliable, because the exit signal and the test signal are both compared with separate threshold values. The higher threshold value is representing a just barely acceptable deterioration of the detection conditions. The exit signal and the test signal are not only occurring synchronously but have the same decisive signal level for comparison with their threshold value. Since the threshold-value for the test signal is higher, the test signal fails to appear as soon as the just barely acceptable deterioration has occurred. The exit signal is still present and can be used in the predetermined way for control purposes. With the failing to appear test signal the alarm signal is generated.The lower threshold value is preferably selected with respect to a worse deterioration of the detection conditions at which a correct operation of the sensor device is no more assured. In the event that the operator has not reacted to the alarm signal, the yarn feeding device, preferably also the textile machine supplied with yarn by said yarn feeding device, can be switched off when the exitspeed signal also fails to appear, in order to avoid emptying of the storing surface.

Alternatively, both signals are compared with the same threshold value according to the method variant of claim 5.

Prior to this comparison, the signal level of the test signal is changed so that upon the comparison of its signal level with the alarm-threshol.d value a precise information is gained indicating the need of the alarm-signal.

The method is particularly useful with opto-electronical and contactless detection in a yarn feeding device comprising an opto-electronic sensor device, according to claims 6 and 9, because there is a well predictable relation between the signal level and the quality of the light transmission.

However, the application of this method and of the structural features for carrying out the method is not limited to an optoelectronical detection, but it is furthermore possible to realise said principle, namely to use an exit signal generated for a predetermined control purpose also for a testing routine, with other contactless detection modes (sound, induction, etc) and even with contacting yarn detection. It is, however, important that the exit signal used for the test routine originates from the detection of the object in the detection zone and shows a well evaluatable signal level which changes with a deterioration of the detection conditions, e.g. by collected dirt, correspondingly. The principle is also useful for yarn feeding devices having a stationary storing surface for the yarn store.The exit signal must not necessarily be a signal chain even, though this might be advantageous in many cases.

With the yarn feeding device according to claim 8, an objectexit signal is used for the testing routine1 which represents the rotational speed of the drum and which occurs exclusively when the drum is driven due to absence of yarn in the detection zone. By means of the test signal the alarm signal can be generated simply and reliably, and exactly at a point in time when the detection condition deterioration reaches a predetermined extent. Of particular usefulness is, that the reliability of operation is only checked when the drive motor is driven for replenishing the yarn store. only then there is considerable risk of emptying the storing surface, because the boundary of the yarn store trails behind the detection zone due to consumption. If the drive motor is not driven, no test routine is carried out.This is then uncritical, because it is a sufficiently big yarn store already on the storing surface, said yarn store reaching into the detection zone. Elimination of the disturbance or cleaning is carried out in the stop intervals of the drive motor so that the yarn feeding device does not have to be switched off, and the production process of the textile machine, which is supplied with yarn by the yarn feeding device, does not have to be interrupted.

In the embodiment of the yarn feeding device according to claim 10, despite the failing to appear of the test signal, the still occurring exit signal is used as a speed signal for controlling. The alarm signal is generated separately. It is useful to use an already provided microprocessor of the control device of the yarn feeding device as the combining-or surveying means for this purpose, because the microprocessor usually has sufficient capacity also for this additional programme routine.

The microprocessor thus only requires a software adaptation.

In the embodiment according to claim 11, the device switches off the yarn feeding device, and, optionally, also the textile machine supplied with yarn from the yarn feeding device, via the switch-off member and as soon as the speed signal also fails to appear, after being compared with the threshold value.

This may happen if, because for other reasons, after occurrence of the alarm signal the disturbance has not been eliminated.

This leads to a dual safety function.

In the embodiment according to claim 12, the voltage transformer produces the same signal level for the exit signal and the test signal. Each comparator compares one signal level with one of two different threshold values. The speed signal then still occurs for control purposes, even when the detection conditions have deteriorated to a just barely acceptable degree. As soon as the test signal fails to appear, the alarm signal will be generated.

In the alternative embodiment according to claim 13, the signal level of the test signal is changed in relation to the signal level of the exit signal already at the voltage divider. The speed signal from the exit signal, for control purposes, can still be derived. With a just barely acceptable deterioration of the detection conditions, the test signal fails to appear and the alarm signal is generated.

In the embodiment according to claim 14, a very reliable, preferably opto-electronical, yarn detection for a precise control of the drive motor is achieved by the plurality of single sensors. However, only the exit signal of one of the single sensors is used for the test routine.

By means of the drawings embodiments of the invention will be described. In the drawings are: Fig l a longitudinal section of a yarn feeding device, Pig 2 a horizontal section in plane 1I-II in Fig 1, Fig 3 a block diagram of a control circuitry Fig 4 a deteil variant of figure 3, and, Fig 5,5A,5B,SC schematic ult-signal diagrams.

A yarn feeding device F according to figure 1, particularly a yarn feeding device for a knitting machine, comprises a housing 13, containing an electrical drive motor 15 for rotatably driving a drum 1 via a shaft 16. Within a holding bracket 13' secured to housing 13 an opto-electronical sensing device 7 is provided containing a plurality of sensors S. Sensor device 7 might be adjusted in a direction parallel to the drum axis.

The sensors S are arranged in circumferential direction of the drum with interspaces, and point towards a detection zone 12 (indicated by a dash-dotted line). Sensor device 7 is connected via control circuitry L to a control device C of drive motor 15. Each of the sensors S may consist of an own light source, e.g. for infra-red light, and of a receiver, e.g.

a photo diode responding to reflected light.

Drum 1 defines a storing surface 2 for a yarn store 5 consisting of windings 6 of a yarn Y which is - for consumption upon demand-withdrawn overhead of drum 1 by the textile machine (not shown), e.g. a knitting machine. Yarn Y is supplied to druid 1 in an upper region of drum 1 in Figure 1 and is wound on by means of the rotation of drum 1. Drive motor 15 is controlled such that it tends to majntain the yarn store 5 in a size with which the yarn store 5 reaches the detection zone 12 despite varying consumption. Ir yarn is present in the detection zone 12, the drive motor 15 is stopped or decelerated. If there is no yarn present in the detection zone 12, the drive motor 15 is driven or accelerated.Via control device C the drive speed of the drive motor 15 is adapted substantially to the yarn consumption.

Drum 1 can be designed as a bar cage with longitudinal bars R separated by interspaces Z. Instead of clear interspaces z also longitudinal grooves could be provided in drum 1, said grooves opening outwardly.

Alternatively, it is possible to use a drum 1 with an even outer surface having surface areas A, B alternating in circumferential direction and having clearly different, e.g.

optical, detection properties. In the shown embodiment bars R and interspaces Z define first and second circumferential sections 8, 9, having said clearly different detection properties for the sensors S of sensor device 7. The surface areas A, B ought to be distributed regularly in circumferential direction. The sensor device 7 of the shown embodiment contains three sensors S which are spaced from each other in circumferential direction such that at least one sensor S is detecting a first circumferential section 8 while at least one other sensor 5 simultaneously is detecting a second circumferential section 9.

In drum 1 a spoke star 19 is provided as an advance element G, The spokes 18 of the spoke star 19 extend through the interspaces Z to a bearing 17 on shaft 16. Said bearing 17 and the spoke star 19 are inclined in relation to the axis 3 of drum 1. Since bearing 17 is mounted on a collar 17a which is hindered to rotate with shaft 16, the spoke star 19 is shifting the yarn store 5 axially in a direction towards detection zone 12, when the drum is rotating. A similar advance effect alternatively could be achieved by a conical design of the drum 1 at the yarn-winding-on side.

The sensors S are commonly provided in a housing 30. Light transparent covering screens 31 or a covering screen common for all sensors S protect the sensors S against direct contamination. On or in front of said covering screens 31 or said common covering screen, and/or in the detection zone 12 of drum 1 lint or contamination may be deposited during operation of the feeding device F.

Figure 3 illustrates schematically in a block diagram a possible embodiment of a control circuitry t for generating drive control signals for drive motor 15 on the basis of the exit signal of sensor device 7 or of the sensors S, respectively.

The sensors S each consist of a sender D7, D8 and D9 and a receiver element TI, T2 and T3, preferably operating with infra-red light. The senders, the receivers and operational amplifiers 20, 21 and 22, co-operating with the receivers, are commonly connected to a source of constant voltage. The received infra-red radiation generates a photo-voltage which influences the voltage at the working resistors. Said voltages are amplified in the operational amplifiers 20, 21 and 22. The exits of the operational amplifiers 20, 21 and 22 are connected via a diode-network with a centrally provided working-resistor 40. The diodes are polarised and inter-connected so that the positive active voltages a::e brought to the upper foot point of and the negative active voltages are brought to the lower foot point of the working resistor 40, respectively.Thus, a maximum differential voltage is generated at working resistor 40. The maximum differential voltage extends between the maximum highest positive voltage and the maximum lowest negative voltage. The positive value is transmitted via an amplifier 38 to a differential amplifier 40, while the negative value is brought to the same differential amplifier 40 via an amplifier 39. The voltage at the exit of the differential amplifier 41 corresponds to the proportional part of the yarn store on the storing surface The voltage at the exit of the differential amplifier 41 is brought via a diode and a resistor-network to a comparator 43. By potentiometer 44 the desired value of the yarn store size can be adjusted.

Comparator 43 supplies the control device of drive motor 15 with two commands: Run or Stop. Detailed information about the design of the circuitry and the function can be found in W095/16628.

The exit signal of one of the sensor elements S (D1, T1) additionally is taken at 14 at the operational amplifier 20 and is brought to a circuit part D as well as to a parallel-circuit part E.

A line 24 connects point 23 with one input of a comparator 26, the other input of which is connected with an adjustable threshold value-member 27. The exit of comparator 26 is connected to a combining - or surveying device V, which, preferably, is integrated in a microprocessor M- Microprocessor N is connected to an alarm-signal-emitter 4 and, optionally, to a switch-off-member 11. The parallel circuit part E branches off at point 23 with a line 25 being connected to one input of a second comparator 28, the other input of which is connected to a second threshold-value-member 29. The exit of the second comparator 28 also is connected to device V.

Threshold-value-member 27 is set for a low threshold value, which, e.g. corresponds with a predetermined signal level.

With a signal level below said threshold value the sensor device 7 would no longer be able to function, e.g. due to deteriorated light transmission quality. Threshold-valuemember 29 is to the contrary set to a higher threshold value representing a just barely acceptable deterioration of the light transmission quality, at which deterioration the sensor device is still able to operate correctly. However, at this condition removing of the contami.nation influencing the light transmission quality is already advisable.

In circuit part D a speed signal is generated on the basis of the exit signal. The speed signal represents the rotational speed of drum 1. The speed signal is provided via the device V of the microprocessor M and can be used for evaluation. The microprocessor compares in an equivalency-logic the occurrence of both signals from comparators 28 and 26. In case both signals become unequal or one of the signals fails to appear, alarm must be initiated.

A test signal is formed synchronously and essentially equal in time-wise relation and with the same signal level as the exit signal. Since threshold-value-member 29 is set to a higher threshold-value than threshold-value-member 27, the test signal fails to appear at the device V as soon as its signal level falls below the threshold-value. By means of the microprocessor X the alarm-signal-emitter 4 is activated in order to, preferably, emit an optical or acoustical signal. If the contamination is not then removed, the microprocessor M may later also activate the switch-off member 11 as soon as also the speed signal fails to appear. The yarn feeding device and the textile machine will then be switched off in order to avoid emptying of the drum 1.

Figure 4 illustrates a variant of the circuit part D and the parallel circuit part E. In line 14 a voltage divider, consisting of resistors 32, 33, 34, is provided At point 35 between resistors 32 and 33 line 24 branches off to one input of comparator 26. At point 37 between the resistors 33 and 34 line 25 branches off to one input of the second comparator 28.

The signal level (voltage level) of the exit signal thus is lower at point 37 (test signal) than at point 35. Each second input of the first and second comparators 26, 28 is connected to a common threshold-value-member 36 set to a pre-determined threshold-value (a reference-voltage). Said threshold value 36 is precisely adjusted to the point at which the contamination reaches a limit at which the contamination is just barely acceptable. When reaching said limit, said threshold value is higher than the signal level of the test signal. By means of the voltage divider 32, 33, 34, comparator 28 "switches" at a higher threshold than comparator 26. In case that the sensor device 27 is contaminated to a just barely acceptable degree, the comparator 28 is no longer able to "switch".By means of the equivalency-examination of the exit voltages of the comparators 26, 28 the microprocessor M determines that an alarm signal has to be emitted. The alarm-signal-emitter is activated.

For a better understanding of the above-mentioned testing routine, Figs 5, SA, 5B and SC are intended. Fig 5 illustrates in a U-t diagram the exit signal 38 in line 14 as it is generated by the sensor S, T1, D1 in dependence on the passing of the circumferential sections 8, 9 or the surface areas A, B, which are different from each other. For both first signal levels the light transmission quality is excellent. Starting with the third signal level in Fig 5, the quality of the light transmission decreases. Within control circuitry L according to Fig 3, exit signal 39 is present, as shown in the diagram of Fig 5A. Threshold value U1 is set at threshold-value-member 27.At the output of comparator 26 occurs a signal train C, while at the output of comparator 28 occurs a signal train C (Fig sic). After point x in time signal train G is no longer present. An examination of equality of the signal trains C, G leads to a logical signal train H according to Fig 5C. At point x in time microprocessor M activates the alarm-signalmember 4.

Threshold U2 represents a just barely acceptable deterioration of the detection conditions, i.e. the light transmission quality, at which the sensor device 7 is able to still correctly operate, as it is shown in Fig 5A, by means of still existing exit signal 39 after point x in time and by signal train C in Fig 5C.

It should be noted that the light transmission quality normally decreases during an essentially longer period of time than can be derived from Figs 5, 5A, 5B, SC. Said figures are schematic with respect to the time-duration and serve only for better understanding.

The diagram according to Fig 5B belongs to the variant according to Fig 4. In Fig 5B, lower part, exit signal 39 is identical to the exit signal 39 of Fig 5A. The threshold value U1 equals the threshold value u1 of Fig 5A. In the upper part of Fig 5B it can be seen that by influence of the voltage divider the signal level of the test signal 40' derived from the exit signal becomes lower than the signal level of the exit signal 39. For test signal 40', the same threshold value Ul is considered as for exit signal 39.The first three signallevels of the test signal 40 are sufficiently high to pass the second comparator 28. The fourth signal level is, however, lower than the threshold value Ul, so that now test signal 40' fails to appear at device V. The alarm signal is generated.

By means of the circuit part D and the parallel circuit part E and their components an anti-valency-checking-device is achieved for evaluating the correspondence between the test signal and the speed signal. Said anti-valency-checking-device can be realised very simply in the microprocessor M by software-adaptation. The examination of the quality of the light transmission is only carried out when the drive motor is driven for replenishing the yarn store, since with stopped drum the sensor device is only detecting the yarn and not the reflecting bars R and cannot reliably judge the quality of the reflection-light-transmission.

The method as explained above can also be used for other physical detecting principles, e.g. when detecting by means of sound, induction, magnetism, capacitance, etc.

Claims (14)

CLAIM

1. A method for surveying the detection-conditions when controlling a yarn-feeding-device, comprising a storing surf ace for a yarn which is stored for feeding purposes in a yarn store consisting of windings, a drive motor for replenishing the yarn store by winding-on yarn, a sensor device directed with at least one sensor onto a detection zone provided in the yarn-feeding-device, and a control circuitry connected to the sensor-device, in which method the sensor is generating an object-exit-signal for control purposes depending on a movement or the presence or absence of an object in the detection-zone, the signal level of which is dependent on the quality of the detection-conditions, and in which at a deterioration of the detection-conditions an alarm-signal can be generated, characterised in that a test-signal is provided on the basis of the object-exit signal substantially synchronously1 that the signal level of the test signal is compared with an alarm-threshold-value representing a just-barely acceptable deterioration of the detection conditions, and that the alarm-signal is generated when the signal level of the test signal falls below the alarm threshold-value.

2. A method as in claim 1, characterised Lfl that the alarm-signal is formed on the basis of the result of a surveillance of the test signal compared with the threshold-value and of the object-exit signal, preferably as soon as the result of the surveillance is failing to appear of the test signal when being compared with the alarm-threshold-value, whilst the object-exit signal is still occurring.

3. fn a method as in claim 1 or 2, characterised in that the storing-surface is rotated by the drive motor during detection of the absence of the yarn in the detection zone surveyed by the sensor-device, and that a speed signal representing the rotational speed of the storing-surface and the test signal are formed from the object-exit signal of the sensor of the sensor device.

4. In a method as in at least one of claims 1 to 3, characterised in that with essentially equal signal levels of the object-exit-signal and the test-signal, the signal level of the test-signal is compared with a higher threshold-value, representing a just barely acceptable deterioration of the detection-conditions, that the signal-level of the object-ex,t-signal or the speed signal, respectively, is compared with a lower threshold value, preferably a threshold value representing a worse no more acceptable deterioration of the detection conditions, that with failing to appear of the test signal the alarm-signal is generated, and that with failing to appear of the object-exit-signal or the speed-signal, respectively, a switch-off-signal (11stop-motion") is generated.

5. In a method as in at least one of claims 1 to 3, characterised in that the test-signal is formed simultaneously with the exit-signal with a signal-level which is lower than the signal level of the exit-signal, and that both signal levels are then compared with the same threshold-value.

6. In a method as in at least one of claims 1 to 5, characterised in that the object or the yarn, respectively, is opto-electronically sensed in the detection zone, and that the alarm-signal is formed when a just barely acceptable deterioration of the quality of the light transmission at the sensor-device occurs.

7. Yarn-feeding-device (F), particularly for knitting machines, comprising a housing (13), a storing-surface t2) for a yarn-store, a controllable drive-motor (15) for driving a winding-on-element for supplying the yarn (Y) to a yarn store consisting of several windings on the storing-surface (2), a stationary signal-generating sensor-device (7) aligned with at least one detection-zone (12) at the storing-surface (2) for sensing the motion or the presence or absence of an object in the detection-zone (12), and a control-circuitry (L) for processing the object-exit-signal of the sensor-device (7), the signal level of the object-exit-signal depending on the detection-conditions at the sensor-device (7), characterised in that in the control-circuitry (L) a parallel-circuit-part ( ) is provided for generating and evaluating a test-signal (20, 20') being essentially synchronously formed from the object-exit-signal (38, 39), and that the control-circuitry (L) is connected to an alarm-signal-emitter (4) which is actuatable at a change of the signal level of the test signal which change represents a just barely acceptable deterioration of the detection-conditions.

8. Yarn feeding device as in claim 7, characterised in that the storing-surface (2) is provided at a drum (1) constituting the winding-on-element and being driveable by the drive-motor (15), that the storing surface (2) has circumferentially disposer surface areas (A, B) with clearly different detection-properties, said surface areas (A, B) defining the object to be sensed with respect to motion by the sensor-device (7) during absence of the yarn (Y) in the detection-zone (12), that by means of the sensor-device (7) an object-exit-signal (38, 39) can be generated during the motion-sensing of the surface areas (A, B), said object-exit-signal representing the rotational speed of the drum (1), that the control circuitry (L) comprises a threshold-value-member (36, 29) for a threshold-value representing a just barely acceptable deterioration of the detection-conditions at the sensor-device (7) and at least one of the surface areas, and that in the control-circuitry (L) means are provided to form the test-signal (20, 20') from the exit signal essentially synchroneously, the test-signal (20, 20') is provided from the exit signal in essentially synchroneously, and that means are provided to compare the signal level of the test-signal with the threshold-value from the threshold-value-member for evaluation.

9. Yarn-feeding-device, as in claim 7, characterised in that the sensor-device (7) is an opto electronical sensor device generating the object-exit signal with a signal-level depending on the light transmission-quality at the sensor-device (7).

10. Yarn-feeding-device, as in claim 7, characterised in that the control-circuitry (L) comprises a circuit part (D) for deriving a speed-signal from the exit signal, that the circuit-part (D) and the parallel circuit-part (E) are commonly connected to a signal processing combining - or surveying-device (V), preferably a microprocessor (M), and that the device (V) is provided with a program-routine within which upon occurrence of the speed signal and failing to appear of the test signal, the alarm-signal-emitter (4) is actuable.

11. Yarn-feeding-device, as in claim 10, characterised in that the combining or surveying-device (V) is connected to a switch-off-member ('sstop-motion") (11) for activation within the program-routine as soon as with driven drive motor (15) also the speed-signal fails to appear.

12. Yarn-feeding-device, as in at least one of claims 7 to 10, characterised in that the circuit-part (D) and the parallel-circuit-part (E) are commonly connected to a voltage-divider, that the curcuit-part (D) is connected to an input of a first comparator (26), the output of which is connected to the device (V), that the other input of the first comparator (26) is connected to a first threshold-value member (27) set for a low threshold-value (U1), preferably a first-reference voltage, and that the parallel-circuit-part (E) is connected to an input of a second comparator (28), the output of which also is connected to the device (V), and the other input of which is connected to a second threshold-value-member (29) set for a higher threshold-value (U2), preferably a second reference voltage.

13. Yarn-feeding-device, as in at least one of claims 7 to 10, characterised in that a voltage-divider (32, 33, 34) for processing the exit-signal is provided, that circuit-part (D) is connected to the voltage-divider upstream a resistor (33) while the parallel-circuit-part (E) is connected to the voltage-divider downstream said resistor (33), that the circuit-path (D) is connected to an input of a first comparator (26), the output of which is connected to the combining - or surveying-device (V), that the parallel-circuit-part (E) is connected to an input of a second comparator (28), the output of which is also connected to the device (V), and that the other inputs of both comparators (26, 28) are connected to a common threshold-value-member (36) set for only one threshold value (Ul), preferably one single reference-voltage.

14. Yarn-feeding-devices as in at least one of claims 7 to 13, characterised in that the sensor-device (7) is provided with a plurality of single sensors (S, T1, T2, T3) which, stationarily are distributed in circumferential and rotational direction of the drum (1), preferably opto electronical sensors, and that the circuit-part (D) and the parallel-circuit-part (E) are connected to only one of the single sensors (S, T1).