Wire presence and identification system

Abstract: A system for detecting the presence of and/or identifying wires (11) at one end of the cable comprises a signal generator (12) for selectively applying an electrical signal to one or more wires at the other end (10a) of the cable. At least one electrode (20) is provided for detecting the electrical signal at the one end (10b) of the cable (10) and electronic circuitry (24 to 32) evaluates the signals coupled to the electrode (20). The signal generator (12) is an ac generator for delivering a ac square-wave signal and the electrode (20) comprises a conductive tube of a predetermined length for inserting a wire (11) at the one end (10b) of the cable. The wire (11) is electrically insulated from the electrode (20) such that the ac signal is capacitively coupled to the electrode (20).

Description: The invention relates to a system for detecting the presence of and/or identifying wires at one end of a cable according to the preamble of claim 1. A system of that kind is known from US-A-4 998 059. A straightforward and long used method for identifying wires of a cable provides for applying a dc or ac signal to one wire or conductor at one end of a cable and to detect the signal on the same wire at the other end of the cable. It is also known to simultaneously apply different signals, for instance signals of different polarity or frequency, to a number of wires at one end of a cable so that the wires can be identified at the other end of the cable by detecting the different signals. When identifying the wires of a cable by means of the signals applied to the wires it is important to establish a good contact with the wires in order to reliably detect the signals. To establish a reliable contact between one or more wires and corresponding electrodes for detecting the signals is particularly difficult if such connections are to be made by an automated assembly process, for instance in a automatic machine for connecting the wires of a cable to a connector. The above-mentioned document, US-A-4 998 059 describes a non-intrusive circuit tracer for positively identifying a conductor at a position remote from a point of injection of a test signal. A tracer signal is alternately injected into two conductors at a rate of alteration which is substantially less than the tracer frequency. For that purpose there is provided a sensor which grasps a cable at a remote point of a bundle of conductors. The conductor is surrounded with enough surface area of a close fitting conductor to cause the injected tracer signal to be capacitively coupled into the probe. Accordingly, the invention is based on solving the problem to provide a system for detecting the presence of and/or identification of wires of a cable which allows a reliable detection and identification in an automatic or semiautomatic manner and by establishing contact with the wires to be detected and identified in a simple and reliable manner. The solution of this problem is characterized in claim 1. Since the connection between the electrode and the wire is made by a capacitive coupling between the wire and the tube walls no metallic contact is required. Accordingly all possible difficulties are avoided which may occur in use of metallic contacts, for instance a high or varying resistance between a conductor and its electrode. For a reliable capacitive "contact" it is merely necessary to introduce a wire into the conductive tube of its electrode. A direct metallic contact in case of a wire without an insulating cover is avoided by the insulating tube of ceramic material closed at the bottom which tube is inserted in the conductive tube of the electrode. Then a wire can symply be pushed down to the bottom of the insulating tube. In this manner a sufficient length of the wire is automatically located in the conductive tube and accordingly a sufficiently strong signal is coupled to the electrode. Further developments of the invention are defined in the subclaims. The ac signal is preferably a square-wave signal having a repetition frequency between 1 kHz and 50 kHz, for instance 5 kHz. In order to facilitate the application of the ac signal from the signal generator to selected wires of the cable a signal routing circuit can be connected between the signal generator and the wires at the other end of the cable, the routing circuit being operable to selectively connect the signal generator to one or more wires. In addition, the signal routing circuit is able to ground all wires which are not connected to the signal generator. In order to detect an ac signal coupled from a wire to its electrode the electronic circuitry comprises for each electrode a series connection of a bandpass filter for pasing only signals having the repetitive frequency of the signal generator, an amplifier and a threshold circuit. The threshold circuit provides an output signal only in case that a wire is inserted in its corresponding electrode and is connected to the signal generator at the other end of the cable. For an automated testing of the wires of a cable, a controller may be provided for receiving, interpreting and displaying the output signals of the threshold circuits and for generating selecting commands for the routing circuit. A further development of the invention is directed to a method for correctly connecting the wires of a cable to contact members of a connector comprising a housing including a guide and locator member and a holding member for the contact members. According to the method, first a predetermined number of wires at one end of the cable are pushed through corresponding individual holes of the guide and locator member. Thereafter the presence of the wires and their correct position in the individual holes of the guide and locator member is detected and identified by means of a system according to the invention. Finally the wires are connected to their associated contact members if the presence and correct position of the wires was verified. For detecting the presence of a predetermined number of wires the signal generator at the other end of the cable is connected to at least one of the wires, and it is checked whether or not an ac signal is capacitively coupled to the electrodes arranged under the holes at the correct positions of the guide and locator member. Thereafter, the individual wires of the predetermined number of wires are identified by connecting the signal generator at the other end of the cable in sequence to the wires one at a time and detecting whether or not a strong ac signal is capacitively coupled to the electrode arranged under the hole at the correct position of the guide and locator member. A preferred embodiment of the invention is described by referring to the drawings in which: Fig. 1 is a block circuit diagram of an embodiment of the invention; Fig. 2 is a cross-sectional view of the electrodes as used for the embodiment of the invention according to figure 1. In fig. 1 there is shown a section of a cable 10 with a number of wires or conductors 11 at both ends of the cable. At one end 10a of the cable 10 a signal generator 12 applies a square-wave signal with a repetition frequency of 5 kHz and a duty cycle of 50 % via a signal router circuit 14 and buffer circuits 16 to selected wires 11. Each wire 11 is connected to a separate buffer circuit which boosts the generator signal before it is injected into the wire. The signal router 14 has the capability either to inject the square-wave signal from signal generator 12 to all wires 11 of cable 10 simultaneously or to inject the signal into only selected ones or only one wire 11. Furthermore the signal router 14 is able to ground all wires 11 into which no square-wave signals are injected. At the other end 10b of cable 10 some of the wires 11 are inserted individually in electrodes 20 arranged in a sensor block 22. Any square-wave signal on wires 11 is capacitively coupled to electrodes 20. This will be described in more detail in connection with fig. 2. The signals coupled to electrodes 20 are applied to active bandpass filters 24 which are tuned to the repetition frequency of signal generator 12, i.e. to 5 kHz in the present example. The square-wave signal of signal generator 12 may have any other repetition frequency between approximately 1 kHz and 50 kHz or even more. Bandpass filters 24 however must be tuned to the respective repetition requency. The output signals of bandpass filtes 24 are each applied to separate amplifiers 26 for amplification of the signals. Amplifiers 26 are followed by individual threshold detectors. The output signal of threshold detectors 28 is a logic signal which is at a first logic state so long as the input signal of the respective threshold detector 28 is below a predetermined threshold and switches to a second logic state if the input signal of the threshold detector is above the predetermined threshold. The predetermined thresholds and the gain of amplifiers 26 are selected in such a manner that the output of each threshold detector 28 is at the first logic state if no signal is coupled to the respective electrode 20, i.e., if no wire 11 is inserted into the electrode 20 or if an inserted wire does not have a sufficiently strong signal on it. If on the other hand a wire couples a sufficiently strong signal to its electrode 20 the output of the respective threshold detector switches to its second logic state. The outputs of threshold detectors 28 are applied to opto-couplers 30 which provide for a potential separation between amplifiers 28 and a controller 32. Controller 32 interprets the output signals of opto-couplers 30 and also generates the commands for controlling signal router 14. Controller 32 includes a program controlled microprocessor (not shown). Fig. 2 shows in greater detail electrodes 20 which are inserted in a sensor block 22. The block forms part of a larger system (not shown) for connecting wires of a cable to a connector. Electrodes 20 each comprise a metal tube 34, for instance a tube made of brass or copper. Inserted in tube 34 is a ceramic tube 36 which is closed at the bottom so that a cavity 38 is formed which is electrically insulated from tube 34. Wires 11 of cable 10 (fig. 1) can be inserted into the cavity 38. If the end of a wire touches the bottom of ceramic tube 36 a predetermined length of wire 11 couples capacitively with tube 34 of electrode 20. In view of the defined lenght of wire 11 introduced into electrode 20 the capacity between a wire 11 and tube 34 is substantially constant so that substantially the same ac signal is coupled to electrode 20 if a wire is fully inserted. Above block 22 there is shown schematically a wire guide and locator member 40 which forms an upper housing half of a connector (not shown) the lower housing half of which holds the contacts (not shown) to which wires 11 are to be connected. The sequence of operations will now be described by referring to fig. 1. All wires 11 at one end 10a of cable 10 are connected to their respective buffer circuits in block 16. At the other end 10b of cable 10 three wires 11 are inserted in corresponding electrodes 20. There is no limitation for the number of electrodes so that there may be more or less than three electrodes for a respective number of wires 11. At first controller 32 commands signal router 14 to apply a 5 kHz square-wave signal via buffer circuits 16 to all wires 11 of cable 10. If a wire 11 is correctly inserted into each electrode 20 an ac square-wave signal will be coupled capacitively to electrode 20 which signal is strong enough to switch the output of threshold detector 30 to its second logic state. In this manner controller 32 detects the presence of wires 11 in electrodes 20. Upon detecting the presence of one or more wires (three in the present case) controller 32 commands signal router 14 to apply the ac square-wave signal to only one wire 11 and to ground all other wires. Accordingly only one wire 11 carries a signal strong enough to switch the output of the appropriate threshold detector 30 associated with electrode 20 into which the respective wire is inserted. In this manner the respective wire can be positively indentified by controller 32. The other wires 11 inserted in electrodes 20 will be similarily identified by applying the ac square-wave signal to the respective wires at end 10a of cable 10. While a grounding of all wires except the one to which the ac square-wave signal is applied will short circuit or at least reduce signals due to a cross-talk between the wires, such grounding may not be necessary in case that the difference in signal strength is sufficient for the wire to which the ac square-wave signal is applied to trigger its threshold detector without affecting the detectors of all the other wires. When connecting wires to the contacts of a connector by means of a system of the present invention two wires 11 are pushed through openings 42 of guide and locator member 40 (fig. 2). The two wires are fully inserted into cavities 38 of electrodes 20. Thereafter the presence of the two wires 11 is detected by means of the circuit arrangement according to fig. 1. Thereafter the correct position of wires 11 in holes 42 of guide and locator member 40 is identified by applying a signal alternately to only one of wires 11. If the positions are correct the two wires can be pulled down and the next two wires can be positioned and checked in the next position of member 40. When all wires have been inserted the machine will cut all wires and connect them to the respective contacts.

Claims: A system for detecting the presence of and/or identifying wires (11) at one end (10b) of a cable (10), the system comprising an ac signal generator (12) for selectively applying an ac signal to one or more wires (11) at the other end (10a) of the cable (10), at least one electrode (20) for detecting the ac signal at the one end (10b) of the cable (10) the ac signal being capacitively coupled to the electrode (20) and electronic circuitry (24 to 32) connected to the electrode (20) for evaluating the signal, characterized in that the electrode (20) comprises a conductive tube (34) of a predetermined length and that an insulating tube (36) of ceramic closed at the bottom to form an electrically insulated cavity (38) for inserting a wire (11) at the one end (10b) of the cable (10), is inserted in the tube (34) such that the wire (11) is electrically insulated from the electrode (20). A system according to claim 1, characterized in that the AC signal is a square-wave signal having a repetition frequency between 1 kHz and 50 kHz. A system according to one of claims 1 to 2, characterized in that a signal routing circuit (14) is connected between the signal generator (12) and the wires (11) at the other end (10a) of the cable (10), the routing circuit (14) being operable to selectively connect the signal generator (12) to one or more wires (11). A system according to claim 3, characterized in that the signal routing circuit (14) grounds all wires (11) which are not connected to the signal generator (12). A system according to one of claims 1 to 4, characterized in that the electronic circuitry comprises for each electrode (20) a series connection of a bandpass filter (24) for passing only signals having the repetition frequency of the signal generator, an amplifier (26) and a threshold circuit (28) providing an output signal only in case that a wire (11) is inserted into its corresponding electrode (20) and is connected to the signal generator (12) at the other end (10a) of the cable (10). A system according to claim 5, characterized by a controller (32) for receiving, interpreting and displaying the output signals of the threshold circuits (28) and for generating selecting commands for the signal routing circuit (14). A method for correctly connecting the wires (11) of a cable (10) to contact members of a connector comprising a housing including a guide and locator member (40) and a holding member for the contact members, the method comprising the steps: a) pushing a predetermined number of wires (11) at one end (10b) of the cable (10) through corresponding individual holes (42) of the guide and locator member, b) detecting the presence of the wires (11) and identifying their correct position in the individual holes (42) of the guide and locator member (40) by means of a system according to one of claims 1 to 6, c) connecting the wires (11) to their associated contact members, if in step b) the presence and correct positions were verified. The method according to claim 7, characterized in that step b) comprises the following steps: i. detecting the presence of the predetermined number of wires (11) by connecting the signal generator (12) at the other end (10a) of the cable (10) to at least one of the wires (11) and checking whether or not an AC signal is capacitively coupled to the electrodes (20) arranged under the holes (42) at the correct positions of the guide and locator member, ii. identifying the individual wires (11) of the predetermined number of wires by connecting the signal generator (12) at the other end (10a) of the cable (10) in sequence to the wires (11) one at a time and detecting whether or not a strong AC signal is capacitively coupled to the electrode (20) arranged under the hole (42) at the correct position of the guide and locator member (40).

Inventors: VAN DESSEL HUGO, VAN DESSEL, HUGO
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1991
Main classification: G01R31
IPC codes: G01R31, H01B13, G01V3, H05K13