Recognition of damage to the jacket of a synthetic fiber cable
Description The invention relates to a device for the recognition of damage to the jacket of a synthetic fiber cable according to the preamble of claim 1. A synthetic fiber cable is a textile product of cable strands of natural or synthetic fibers, manufactured by shaping the cable without twisting, by braiding in two or more stages and / or coating, or by interlacing. The jacket surrounds and protects the cable structure composed of the so-called synthetic fiber cords and, in the case of driven cables, generates the necessary traction capacity. Preferably it is made of an abrasion-resistant plastic and is bonded by adhesion and / or in a positive fit with the outer cord layer. The cable jacket wraps either the cable as a whole or the outer cables of the cable with a plastic jacket, together forming the cable jacket. The cable jacket is subjected to a strong abrasive wear, especially in the cables directed and / or driven by pulleys. With the document EP 0 731 209 Al of the applicant, a synthetic fiber cable with jacket has been disclosed as a support member for elevators. In this drag cable, the sleeve is divided coaxially by colors to recognize its state of wear. With a corresponding wear of the jacket, the color below appears, which indicates the existence of an advanced wear of the cable. This indication of damage has given good results in the event of wear phenomena of the cable, but is only suitable for reliably recognizing local limited damage, for example due to inadvertent contact with sharp edges or the like. Therefore, the invention aims to propose a device for the recognition of damages of a cable jacket, which reliably recognizes the deterioration of said jacket regardless of the cause thereof. This objective is solved by the features indicated in claim 1. The damage recognition according to the invention has different advantages. The controlled breaking element inserted in the cable jacket allows a permanent monitoring of the jacket with measurement technique. To do this, a signal is transmitted through the controlled breaking element along a given cable length. The interruption of this connection means that the cable jacket has been damaged from the outside. Through real-time monitoring, visual control is not necessary until the surveillance apparatus detects a deterioration of the cable jacket. The controlled breaking element may be configured in the form of an electrical conductor, optical conductor or the like. In the choice of the conductive material used, it is essential that it present an alternative bending fatigue resistance that corresponds at least to the strength of the cable structure, to exclude the possibility of a material failure due to the service conditions. For example, the controlled breaking element can be configured as an electrical conductor in the form of a carbon fiber or a metallic wire, through which a control signal is sent. If the connection is interrupted, no signal is transmitted, which can be indicated appropriately. Acting together with a control device, damage to the cable jacket can be detected by the control system and appropriate measures can be taken without delay to ensure a safe elevator service. The transmission element is preferably wound around the entire cable or the cords of the outer layer and covered by the cable jacket preferably applied with the pressurized injection process. Furthermore, in a two-layer cable jacket embodiment, the controlled break member may be disposed on the inner layer of the shirt and covered by the second layer. The controlled breaking element is completely embedded in the cable jacket and the additional transverse forces acting on the synthetic fiber cords when the cable runs on pulleys are avoided. In another preferred embodiment there are several controlled breaking elements embedded in the jacket parallel to the cords and / or around the cable in the longitudinal direction thereof. This embodiment offers the advantage of a surveillance covering a large area of the cable jacket with respect to mechanical damage produced from the outside. The embodiments of the invention in which the conductive element is formed by a high strength material, offer the additional advantage of compacting or reinforcing the cable jacket. In this way, the alternative bending strength and the abrasion behavior of the cable jacket can be improved. The invention is explained in more detail below with reference to an exemplary embodiment and with reference to the accompanying drawings. The figures show: Figure 1, a multilayer aramid fiber cable with a transmission element inserted in the cable jacket and wound helically around the cable. - Figure 2, a schematic of a monitoring circuit for the aramid fiber cable represented in Figure 1. - Figure 3, a circuit diagram of a control circuit. The perspective representation of Figure 1 shows the structure of a cable of aramid fibers 1 with a jacket, consisting of strands of aramid fibers 2 arranged in layers together with filler cords 3 around a core 4. Between a layer of cords 5 and an outer cord layer 6 is provided with an intermediate sleeve 7 which is preferably profiled. The outer cord layer 6 is covered by the cable jacket 8, preferably of polyurethane or polyamide. A copper wire 9 is wound helically around the outer cord layer 6, along the entire cable, for example with a pitch 10 of 1 to 4 turns per 60 mm of cable length. The cable jacket 8 is extruded on the copper wire 9, so that said copper wire 9 is embedded in the material of the jacket and covered by it. When several controlled breaking elements are used, they can in principle be arranged in any way in the cable jacket as long as they establish a signal transmission connection along a given length of cable and that the material of the jacket surrounding them prevent the contact of the controlled breaking elements with each other. Instead of winding it around the cable 1, the copper wire 9 can also be embedded in the cable jacket 8 parallel to the cords of aramid fibers 2 of the outer cord layer 6. However, in a parallel arrangement of this It is convenient to provide multiple copper wires uniformly distributed in the perimeter of the cable 1, so as to achieve a monitoring that covers the largest possible area of the cable jacket 8. In this respect, this arrangement is especially advantageous in the case of a structure of twisted or twisted cable, since, due to the torsion angle, an oblique position of the copper wires 9 - or in general of the transmission elements - with respect to the direction of movement of the driven cable 1 is achieved. Thanks to this oblique position, an object that linearly rubs the driven cable 1, such as a cutting edge, will necessarily separate the copper wires, which will be immediately recognized as damage. Figure 2 shows the measurement technique monitoring of the aramid fiber cable shown in figure 1. To check whether the connection established by the controlled breaking element (s), in this case a copper wire 9, is intact along the length of the cable 1 or along a determined section of the cable, in a control circuit 11 for example an electrical voltage can be applied at both ends of the transmission element. As a voltage source, for example, a battery 12 or voltage generator can be used. With the aid of an ammeter 13 it can be checked whether current flows or not through the copper wire 9. Instead of the ammeter 13 a control lamp can be connected to the electrical circuit which, in case of damage and interruption of the transmission path, turn off or on depending on the type of connection. In addition, damage to the cable jacket 8 can be recognized with the aid of a control connection 21 connected in the monitoring circuit 11. For example, a suitable connection for this purpose has been disclosed with EP 0 731 209 A1. In this known control connection 21, shown in Figure 3, a constant current 15 is applied to the transmission element (s) 9, for which each transmission element 9 represents a resistance R1 to Rn. A low-pass filter 16 filters the incoming pulses and leads them to a threshold value switch 17. The threshold value switch 17 compares the measured voltages. When specific limit values are exceeded, that is to say, due to a breakage of the transmission elements 9, the resistance becomes so great that the admissible voltage value is exceeded. This exceeding of the limit value is stored in a non-volatile memory 18. This memory 18 can be deleted by means of a reset key 19, or the memory transmits its information to a logic 20 connected to the elevator control. Each transmission element 9 is properly wired and constantly checked. As soon as damage appears, the elevator control disconnects the elevator by driving the cabin to the evacuation position and immobilizing it there.