Testing Device for Hydraulic Rope System Tensile Force Equalizing Unit

Rope elevators, also referred to as traction elevators, have a cabin suspended from a system of ropes. The system of ropes consists of at least two load-bearing steel ropes with six strands or, from the point of view of easier bending, and currently more widespread, ropes with eight strands. Lifting or lowering of the car, run between the guides, is ensured by the frictional force of the steel ropes in the grooves of the traction disk of the elevator machinery. As the load-bearing capacity of the elevator increases, the required number of load-bearing ropes also increases, especially in the case where small diameter ropes are used in traction elevators. The actual weight of the car and the weight of the load must be evenly distributed among all supporting ropes that are used in the given layout of the elevator. Currently, several principles are known by which it is possible to detect and also change the values of the instantaneous magnitudes of the tensile forces acting in a system of ropes. The paper describes the principle of operation of hydraulic balancing of tensile forces in the system of supporting ropes, which uses the laws of hydromechanics and knowledge of pressure transfer to any place in the fluid, known as Pascal’s law. Balancing of differently set values of tensile forces in three supporting ropes, to values of the same size, can be simulated on a test device. This presents the correct operation of the hydraulic system and the possibility of balancing tensile forces in the system of supporting ropes described by the principle of hydraulic device.


Introduction
The traction capacity of rope elevators is defined by the fact that it is possible to transfer the force between the support means (steel ropes) and the grooves of the traction disc by friction, see Figure 1. Mobile mechanical [7] and hydraulic [9] tensile force equalizers, which allow to detect and equalize tensile forces in the system of supporting ropes of elevators, are described in [1][2][3][4][5].
The article [1] describes an apparatus that allows an even distribution of the strain into lift carriers, which use springe hinge of carrier ropes.
The methodology described in the article [2] by which it is possible to compare different tensile forces that are caused by the uneven distribution of loads in carrier ropes of lifts. In order to compare the applied tensile forces in a certain number of carrier ropes, it is possible to use the device called "rope hydraulic tension compensator," when, for example, building new elevators, changing carrier ropes during renovations or servicing existing lifts.
The paper [3] describes the basic principles of devices currently in use, the so-called rope tensioners, which allow detecting and adjusting primarily different tensile forces in the hoist ropes to the same value. The paper refers to two, already published design variants of portable rope straighteners, which use foil strain gauges or strain gauge sensors to detect the acting tensile forces [1] in the hoist ropes [2].
A specific design and technical solution of the device for detecting and offsetting tensile forces in the elevator carrier ropes is described in [4,5]. The described device [4] is capable of continuously recording the time course of the in-stantaneous tensile forces, acting on elevator carrier ropes, when one free ends of the carrier ropes are mechanically attached to the openings of the suspension screws, which are mechanically tied to the bearing bracket [5].
The authors of this paper have not been able to find any other references that would describe a device that allows to obtain satisfactory results of balancing the tensile force of ropes.
The above-mentioned design principles of tensile force equalizers in the system of elevator supporting ropes are devices that are installed at the end points of the threaded parts of the suspension bolts, which are threaded through the holes in the supporting brackets. Hexagon nuts are screwed onto the shank of the suspension bolts in the space above the upper surface of the bracket to prevent the threaded parts of the shank bolts from sliding out of the holes in the brackets.
The advantage of mobile equalizers is that, after precise distribution of tensile forces into individual cross-sections of ropes, the equalizers are dismantled from rope suspensions and can be moved to another elevator, where the load is distributed unevenly into supporting ropes.
The device described in [8], developed for balancing tensile forces in a system of supporting ropes, has not found application in traction elevators, and is, therefore, not commonly used for balancing tensions in elevator ropes. However, the application of a hydraulic tensile force compensator in ropes has found application and is commonly used in mining equipment with friction discs.

Testing device designed to equalize tensile forces in ropes
The testing device, see Figure 2 and Figure 3, consists of a welded steel frame structure I, which consists of stands, upper and lower platform; hydraulic unit II with hydraulic cylinders 2.1 to 2.3 [12]; and measuring apparatus III with tension force sensors 12.1 to 12.3 [13]. The upper platform of the frame structure I is welded from nine pieces of TR 4HR 40 × 3, the lower platform is also welded from nine TR 4HR 40 × 3 profiles. The upper and lower platforms are 1.200 mm apart; this distance is defined by stands made of TR 4HR 40 × 3 profiles.
Seven suspension nuts M8 (ČSN 021669) are attached to the profile 1.2 of the upper platform of the steel frame structure I by means of three M8 × 55 screws. Carabiners are threaded into the eyelets of the suspension nuts, which at the same time are also threaded into the eyelets of the suspension bolts. The threaded parts of the suspension  Hanging screws are screwed into each sensor 12, into a hole with an internal thread M8 × 1.25 in their lower faces. The carabiners are threaded through the eyes of the suspension bolts, and the carabiners are also threaded through the rope eyelets. The ends of the six-strand steel ropes 8 are threaded through the cable eyelets of the construction 6 × 19M -WSC [6,11] (of nominal diameter 4 mm, nominal strength of wires 1.77·10 9 Pa, and minimum breaking forces 10.25·10 3 N), which are terminated by eyes by rope clamps. The other ends of the steel ropes 8 are threaded onto carabiners. Rope eyelets are threaded onto the carabiners, which form the eyes of the suspension bolts. The rope 8 is connected to the eye by three rope clamps. To form eyelets at both ends of all three steel ropes 8, three pieces of rope clamps are used (rope clamps 14 reduce the load-bearing capacity of the rope to 50%).
The threaded parts of the suspension bolts are slid into holes ϕ 9 mm in the brackets 17, see view B in Figure 2 shown for the hydraulic cylinder 2.1. To prevent the hinge screw from sliding out of the piston rod bracket 17, a nut 15 is threaded on the threaded part of the hinge screw 11 from the inner underside of the bracket surface 17 and a nut 16 is screwed on. The bracket 17 is mechanically connected to the piston rod of the hydraulic cylinder 2.1 by a pin 20 (ϕ = 16 mm). To prevent the pin 20 from sliding out of the holes in the bracket 17, the pin 20 is fitted on the left and right sides with a washer 19 and a cotter pin 18.
The interconnection of the profile 1.2 of the upper platform of the steel construction I with one of the three hydraulic cylinders 2.1 to 2.3 is secured by the interconnection of machine parts (see central upper view in Figure 2) screw, suspension nut, carabiner, steel rope 8, carabiner, suspension screw, tensile force sensor 12, suspension screw, bracket, pin and piston rod of hydraulic cylinder 2.
The bodies of the hydraulic cylinders 2.1 to 2.3 are mechanically connected by pins 20 to the brackets 17, see view C in Figure 2. M8 × 70 22 screws are threaded through a ϕ 9 mm hole in the brackets 17, their shafts passing through holes in the profile 1.11 of the lower platform of the steel construction I. Washers 15 are threaded on the threaded part of the screws 22 protruding from the lower part of the profile 1.11.
The prestressing of the rope 8, the so-called derivation of a certain magnitude of the tensile force F i [N] in the rope 8, is achieved by tightening the screw against the profile 1.2 of the upper platform, or the screw against the profile 1.11 of the lower platform, of the frame construction I of the test device designed for equalizing tensile forces in the ropes.
If, in the case of "i" identical hydraulic cylinders, the spaces under the pistons are filled with fluid, then at different tensile forces F i [N] in the "i" support ropes (assuming prevention of leakage of hydraulic fluid from the spaces under the hydraulic cylinder pistons), different pressures p i [Pa] are derived in "I" hydraulic cylinders. A higher tensile force in the "i" support rope mechanically transmitted to the piston rod of the hydraulic cylinder exerts a higher pressure in the space under the piston of the body of this hydraulic cylinder than a tensile force of lower magnitude, see (1). If the different "i" pressures under the pistons "i" of the hydraulic cylinders are to be equalized, it is necessary to interconnect the spaces under the pistons, see Figure 5, of all hydraulic cylinders by hydraulic lines, which are a part of the hydraulic unit II, see Figure 4.

Hydraulic unit of testing device designed to equalize tensile forces
The hydraulic unit II, see Figure 4, of the testing device for tensile force in the ropes makes it possible to achieve, in the final state, the setting of equal magnitudes of tensile forces F i [N] in the "i" load-bearing ropes (i.e., the rope system, see Figure 1, which were different in the initial state). The magnitude of the pressure p 0i [Pa] in the i th hydraulic cylinder (where i = 1 to 3) is given by the size of the tensile force F i [N] (must by less than Fmax [N]), which acts in the i th load-bearing rope, see (1): When extending the piston rods from the hydraulic cylinder bodies 2.1 to 2.3, underpressure occurs in the spaces above the pistons of the hydraulic cylinders 2, due to which hydraulic fluid is sucked from the tank of the manual pump 3 through the lines (shown on Figure 5a and Figure 5b in red) and injected above the pistons of the hydraulic cylinders 2.
As the pistons slide into the hydraulic cylinders 2.1 to 2.3, the hydraulic fluid is pushed out of the space above the pistons and taken by the lines to the reservoir of the manual pump 3.

Experimental measurement of tensile forces in ropes
Experimental measurement performed on the testing device (see Figure 8) was undertaken in three separate and independent experiments.   Figure 6. Tensile forces in ropes 8 detected by sensors 12 derived from fluid pressure in hydraulic cylinders 2 *2 see Figure 7. Tensile forces in ropes 8 detected by sensors 12

I. Experimental measurement
With valves 4.1 to 4.3 closed and a gradual tightening of the screws 7 against the suspension nuts 9 in the rope tensile force testing device, see Figure 2, differing tensile forces F i [N] (where i = 1 to 3) were derived in individual cross-sections of the load-bearing ropes 8 [11], see Figure 2. The maximum tensile force F sD [N], which it was possible to generate in the rope, was given by m sD = 250 kg (F sD = 2.45·10 3 N), the load permitted by the tensile force sensor 12 [13].
The    Figure 9, *2 see Figure 10, and Figure 11 Figure 10 and Figure 11    see (4): Under the assumption that the fluid volume in the inlet lines Vp [m 3 ] of the hydraulic unit is equal to the volume of fluid under the piston 2.1 of the hydraulic cylinder V v1 [m 3 ], this means V v1 = Vp = V [m 3 ], relationship (4) can be modified into the form of (5), which is equal to the relationship (2):  (5) and Table 2.  (7) and Table 3.
Under the assumption that the fluid volume in the inlet lines Vp [m 3 ] of the hydraulic unit is equal to the volume of fluid under the piston 2.2 of the hydraulic cylinder V v2 [m 3 ], this means V v2 = Vp = V [m 3 ], relationship (7) can be modified into the form of (8): With a drop in pressure p 02 [Pa] under the piston of cylinder 2.2 to a pressure value of p 2 [Pa], a change in tensile force occurred in rope 8.2, to the value F 2k [N], see (9) and Table 3.  Table 4.
Under the assumption that the fluid volume in the inlet lines Vp [m 3 ] of the hydraulic unit is equal to the volume of fluid under the piston 2.3 of the hydraulic cylinder V v3 [m 3 ], this means V v3 = Vp = V [m 3 ], relationship (10) can be modified into the form of (11): Figure 10 and Figure 11 show the graphical course of the magnitude of the tensile forces in ropes 8i, registered by the tensile force sensor 12i (see Figure 2) in the Dewesoft X2 SP5 software environment.

III. Experimental measurement No. 3
With valves 4.1 to 4.4 closed, the screws 7i were gradually tightened against the nuts 9.1 in the rope tensile force testing device, see Figure 2. By tightening of the screws 7i, tensile forces F i [N] (where i = 1 to 3) were derived in ropes 8i, which were registered by the tensile force sensors 12i.
The magnitudes of tensile forces F i [N] were recorded in Table 5. According to the relationship (1), pressures p 0i [Pa] below the cylinder pistons 2i were calculated. The theoretically calculated pressures p 0i [Pa] were verified with the pressures measured p 5.i [bar] by the pressure gauges 5i.

Conclusion
The paper deals with a test device, the so-called hydraulic rope tensile force equalizer, which can equalize (originally different magnitudes) tensile forces in ropes by changing the fluid pressure in interconnected hydraulic cylinders.
The second section of this paper presents a 2D structural design as well as a 3D model of the test equipment and lists and describes the basic machine components that were used to implement a laboratory model of a hydraulic equalizer of tensile forces in ropes.
Part of the paper is a description of the interconnection of hydraulic elements and a description of the operation of the hydraulic unit, which brings fluid from the tank to these elements under the pistons of hydraulic cylinders.
The main part of the paper is a section in which the procedures of three performed experimental measurements are defined, which were undertaken to verify the correct functionality and simulate the operation of the hydraulic equalizer of tensile forces in ropes.
The possible way of how to achieve uniform load distribution into two or more carrier ropes in the traction lift using a rope hydraulic tension compensator is given in the text of this paper.
If the pressure in the liquid is reached below the pistons of hydraulic cylinders, then the compressive force (proportional to the highest value of all the loads acting on all the springs before installation of tension compensator) acts on the first most compressed spring. Also, for all other springs of all suspension bolts, this pressure force acts when the pressure in the liquid is reached below the pistons of the hydraulic cylinders.
By increasing the applied pressure under the pistons of the hydraulic cylinders above the pressure, all the springs are compressed by the compressive force transmitted by the cylindrical bodies from the hydraulic cylinders.
If a uniform load distribution to all cross-sections of carrier ropes is achieved as described above, all components of the rope hydraulic tension compensator must be removed from the screw hinge of carrier ropes. When disassembling, it is necessary to extend all piston rods from hydraulic cylinders to the maximum possible position. This is ensured by the hydraulic power unit. The lever of the manual hydraulic pump pumps the hydraulic fluid through a line through the open one-and the two-way valve (adjusted to a suitable position) to the quick coupling. A hydraulic hose is connected to the quick coupling, which supplies the liquid above the pistons of hydraulic cylinders. Another hydraulic hose connects the spaces under the pistons of hydraulic cylinders. The fluid from under the pistons of hydraulic cylinders is discharged through the hydraulic hose to the quick coupling. The hydraulic fluid is routed via a pipeline in the hydraulic power unit via a two-way valve (adjusted to a suitable position into the hydraulic pump tank.
In contrast to the known principle of the hydraulic compensator, the described device can be provided with strain gauge load cells that can detect instantaneous tensile forces in carrier cables, record them, and use them for certificate processing purposes.
The described rope hydraulic tension compensator can fully fulfill the function for which it has been designed without the use of strain gauge load cells. If the compensator is not equipped with a strain gauge, then the piston rod of the hydraulic cylinder is connected to the cylindrical body mechanically. The threaded end portion of the shank of bolt is screwed onto the internal thread of the body.
Double-acting hydraulic cylinders, which equalize the initially different tensile forces in the ropes to the same values, are connected via hydraulic pressure hoses to the hydraulic power unit. With the hydraulic power unit, the hydraulic fluid is pumped from the tank through the manual hydraulic pump via suitably open or closed hydraulic valves to the spaces below or above the hydraulic cylinder pistons. In the "under/above the piston" space of cylinders, where the hydraulic fluid pressure is supplied by the hand pump, the piston moves in the cylinder, and the hydraulic fluid from the "below/above the piston" space moves to drain the hydraulic fluid back into the tank.
The device described in this paper, developed for balancing tensile forces in a system of supporting ropes, has not found application in traction elevators and is therefore not commonly used for balancing tensions in elevator ropes. However, the application of a hydraulic tensile force compensator in ropes has found application and is commonly used in mining equipment [13] with friction discs.