A kind of advanced support monorail hydraulic anchor drilling vehicle

Abstract

The invention discloses an advanced support monorail hydraulic anchor drilling vehicle, which relates to the technical field of tunnel excavation machinery, including an anchor drilling vehicle body and an advanced support platform, the anchor drilling vehicle body includes a main frame, an airborne platform and a power station assembly, the power station assembly is installed at the rear end of the main frame, the front end of the main frame is provided with a gantry telescopic beam, the bottom of both ends of the gantry telescopic beam is provided with gantry legs, and the rear end of the main frame is also provided with a main frame rear leg; a translation telescopic arm is installed on the gantry telescopic beam, the translation telescopic arm is connected to a first spiral swing oil cylinder, the first spiral swing oil cylinder is connected to a second spiral swing oil cylinder, and a mounting seat that can be connected to the advanced support platform is installed on the second spiral swing oil cylinder; the airborne platform is installed on the main frame and can move along the main frame, and an anchor drilling machine is installed on the airborne platform. The invention can realize "long excavation and long support", ensure the reliability of tunnel roof support, and improve the safety of the working environment.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel excavation machinery, in particular to an advanced support monorail hydraulic anchor drilling vehicle. Background Art

[0002] At present, the "short excavation and short support" technology is usually used for rapid excavation in coal mines. However, the "short excavation and short support" technology has the following disadvantages:

[0003] 1) "The empty top time is long". The excavation process is to dig first and then support. The net support can only be hung after the excavator stops cutting.

[0004] 2) "Low production efficiency". The integrated digging and anchoring machine, fast digging and anchoring equipment, and the digging and supporting of the head and top plate are integral structures or partially split structures (tunnel boring machine + crawler anchor drilling vehicle). The digging and supporting process is carried out in a front-to-back order. In the integral digging and anchoring structure, cutting stops, the machine-mounted support falls forward, and the steel belt and steel mesh are manually laid on the machine-mounted support, and the support is lifted to support the top plate; in the split structure, the process is divided into front and back, the anchor drilling vehicle and the tunnel boring machine must alternate, the temporary support hangs the steel belt and lays the mesh, the personnel frequently go up and down, and the equipment frequently goes up and down, the empty top time is longer, and there is more time for useless work; the digging and supporting cycle is frequent, the labor intensity is high, the manpower is high, and there is a lot of useless work going up and down, and the production efficiency is low.

[0005] 3) "Short excavation and short support", excavation and support cannot be synchronized, they can only be excavated first and then supported, the anchor row spacing in each cycle can only be single row or 2 rows, and the number of cycles is large! After the excavator stops cutting, the roof is in an empty state for a "long time", which is very dangerous, especially under bad roof conditions, and is always facing collapse, endangering the safety of personnel and equipment. There are great safety hazards in the empty roof, so "short excavation and short support" can only be implemented.

[0006] 4) There are great safety hazards. All the equipment are running on the bottom plate of the tunnel. The equipment are all running on the bottom plate, and the vehicles frequently pass each other. The visibility underground is poor, and there is a risk of equipment collision. The passing of vehicles causes the empty top to last for a long time and the roof collapses. The integral structure of the excavation and anchoring has a large cutting force during excavation and cutting. The cutting arm swings left and right and rises and falls up and down. If the platform supports the roof at this time, the swing of the cutting arm will stir the roof structure, making it easier to damage the roof and accelerate the collapse of the roof.

[0007] Therefore, it is urgent to provide a novel advance support monorail hydraulic anchor drilling vehicle to solve the above-mentioned problems existing in the prior art. Summary of the invention

[0008] The purpose of the present invention is to provide an advanced support monorail hydraulic anchor drilling vehicle to solve the problems existing in the above-mentioned prior art, to achieve "long excavation and long support", to ensure the reliability of tunnel roof support, and to improve the safety of the working environment.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] The present invention provides an advanced support monorail hydraulic anchor drilling vehicle, comprising an anchor drilling vehicle body and an advanced support platform, the anchor drilling vehicle body comprising a main frame, an airborne platform and a power station assembly, the power station assembly being installed at the rear end of the main frame, the front end of the main frame being provided with a gantry telescopic crossbeam, the bottoms of both ends of the gantry telescopic crossbeam being provided with gantry legs, the rear end of the main frame being further provided with a main frame rear leg, the main frame rear leg being capable of supporting a tunnel roof; a translation telescopic arm being installed on the gantry telescopic crossbeam, the translation telescopic arm being connected to a first spiral swinging oil cylinder, the first spiral swinging oil cylinder being connected to a second spiral swinging oil cylinder, the second spiral swinging oil cylinder being provided with a mounting seat capable of being connected to the advanced support platform; the airborne platform being installed on the main frame and capable of moving along the main frame, the anchor drilling rig being installed on the airborne platform.

[0011] Preferably, driven wheels are installed on the main frame and the power station assembly, and the driven wheels can be installed on a track beam, and the track beam is installed on the tunnel roof.

[0012] Preferably, the power station assembly includes a hydraulic system, an electrical system and a drive assembly, and the drive assembly is connected to the main frame; the drive assembly is equipped with drive wheels, and the drive wheels are installed on both sides of the track beam.

[0013] Preferably, a hydraulic lifting hoist is installed on the track beam, and the track beam is equipped with a track derailer.

[0014] Preferably, the airborne platform is connected to the main frame via wing arms, front legs of the airborne platform are installed on both sides of the front end of the airborne platform, and rear legs of the airborne platform are installed on both sides of the rear end of the airborne platform.

[0015] Preferably, an airborne platform telescopic arm is provided on the airborne platform, and the airborne platform telescopic arm is connected to the anchor drilling rig.

[0016] Preferably, the translational telescopic arm is connected to the first end of the first spiral swing cylinder through a four-bar linkage, and the first spiral swing cylinder is horizontally arranged; the second spiral swing cylinder is vertically arranged, and the bottom end of the second spiral swing cylinder is connected to the second end of the first spiral swing cylinder.

[0017] Preferably, a pressure sensor is installed on the top of the second spiral swing cylinder, and the mounting seat is installed on the pressure sensor.

[0018] Preferably, a driver's seat is installed on the gantry telescopic crossbeam.

[0019] Preferably, the advance support platform comprises a crossbeam assembly, a longitudinal beam assembly, a left support frame assembly and a right support frame assembly, and the longitudinal beam assembly, the left support frame assembly and the right support frame assembly are all mounted on the crossbeam assembly.

[0020] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0021] 1) Passing vehicles in the upper and lower spaces of the tunnel to save space and achieve green mining;

[0022] 2) Seamless butt joint, zero head clearance;

[0023] 3) The monorail anchor drilling rig program controls the advance, retreat, lifting and cutting of the tunnel boring machine. The tunnel boring machine is unmanned, has interlocking functions, good safety performance, and realizes intelligent replacement of personnel;

[0024] 4) Parallel operation improves efficiency. When the front part of the tunnel boring machine is cutting, the anchor drilling machine at the rear of the monorail anchor drilling machine will drill the top side anchor bolts and cables later;

[0025] 5) Transport support materials to the working surface.

[0026] 6) The monorail crane auxiliary transportation system is formed in the excavation tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a structural schematic diagram of the advanced support monorail hydraulic anchor drilling vehicle in the present invention;

[0029] Figure 2 A top view of the advanced support monorail hydraulic anchor drilling vehicle of the present invention;

[0030] Figure 3 It is a structural schematic diagram of the anchor drilling vehicle body in the present invention;

[0031] Figure 4 It is a front view of the anchor drilling vehicle body of the present invention;

[0032] Figure 5 It is a top view of the anchor drilling vehicle body of the present invention;

[0033] Figure 6 It is a side view of the anchor drilling vehicle body of the present invention;

[0034] Figure 7 It is a front view of the advanced support platform in the present invention;

[0035] Figure 8 It is a top view of the advanced support platform in the present invention;

[0036] Fig. 9 It is a side view of the advanced support platform in the present invention;

[0037] Fig.10 It is a schematic diagram of the first application example of the advanced support monorail hydraulic anchor drilling vehicle in the present invention;

[0038] Fig.11 It is a schematic diagram of the second application example of the advanced support monorail hydraulic anchor drilling vehicle in the present invention;

[0039] Fig.12 It is a schematic diagram of the third application example of the advanced support monorail hydraulic anchor drilling vehicle in the present invention;

[0040] Fig.13 It is a schematic diagram of the fourth application example of the advanced support monorail hydraulic anchor drilling vehicle in the present invention;

[0041] In the figure: 1-advance support platform, 101-right support frame assembly, 102-beam assembly, 103-longitudinal beam assembly, 104-left support frame assembly, 105-side support leg, 106-side support, 107-side support adjustment cylinder, 2-anchor drilling vehicle body, 201-main frame, 202-airborne platform, 203-airborne platform telescopic arm, 204-airborne platform front support leg, 205-airborne platform rear support leg, 206-gantry telescopic crossbeam, 207-gantry support leg, 208-four-bar linkage, 209-first spiral swing cylinder, 210-second spiral swing cylinder, 211-pressure sensor, 212-mounting seat, 213-anchor drilling rig, 214-main frame rear support leg, 215-wing arm, 216-driver's seat. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The purpose of the present invention is to provide an advanced support monorail hydraulic anchor drilling vehicle to solve the problems existing in the prior art, to achieve "long excavation and long support", to ensure the reliability of tunnel roof support, and to improve the safety of the working environment.

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] like Figure 1-9 As shown, this embodiment provides an advanced support monorail hydraulic anchor drilling vehicle, including an anchor drilling vehicle body 2 and an advanced support platform 1. The anchor drilling vehicle body 2 includes a main frame 201, an onboard platform 202 and a power station assembly. The power station assembly is installed at the rear end of the main frame 201. The front end of the main frame 201 is provided with a gantry telescopic crossbeam 206. The bottom of both ends of the gantry telescopic crossbeam 206 is provided with gantry legs 207. The gantry telescopic crossbeam 206 can control the gantry legs 207 to extend and retract horizontally to adapt to different tunnel sections. The rear of the main frame 201 is provided with a gantry telescopic crossbeam 206. A main frame rear support leg 214 is also provided at the end, and the main frame rear support leg 214 can support the tunnel roof; a translation telescopic arm is installed on the gantry telescopic beam 206, and the translation telescopic arm is connected to a first spiral swing cylinder 209, and the first spiral swing cylinder 209 is connected to a second spiral swing cylinder 210, and the second spiral swing cylinder 210 is installed with a mounting seat that can be connected to the advance support platform 1; the airborne platform 202 is installed on the main frame 201 and can move along the main frame 201, and an anchor drilling rig 213 is installed on the airborne platform 202.

[0046] In this embodiment, driven wheels are installed on both the main frame 201 and the power station assembly. The driven wheels can be snap-fitted and installed on the track beam, and the track beam is installed on the tunnel roof. Two or more groups of driven wheels are arranged on the main frame 201; the power station assembly includes a hydraulic system, an electrical system and a drive assembly. The drive assembly is connected to the main frame 201 as a whole through a connecting rod assembly. One or more groups of drive wheels are installed on the drive assembly, and the drive wheels are installed on both sides of the track beam; the hydraulic system can provide hydraulic pressure to and control each hydraulic component, and the electrical component can supply power to and control each electrical component.

[0047] In this embodiment, a 5-ton hydraulic lifting hoist is installed on the track beam, which can transport materials within 200 meters behind the tunnel boring machine and reduce the labor intensity of workers.

[0048] In this embodiment, the airborne platform 202 is connected to the main frame 201 through the wing arms 215, and the front legs 204 of the airborne platform are installed on both sides of the front end of the airborne platform 202, and the rear legs 205 of the airborne platform are installed on both sides of the rear end of the airborne platform 202. The front legs 204 and the rear legs 205 of the airborne platform can be extended downward to press against the ground to stabilize the fuselage.

[0049] In this embodiment, an airborne platform telescopic arm 203 is provided on the airborne platform 202, and the airborne platform telescopic arm 203 is connected to the anchor drill rig 213 and can be extended forward to drill multiple rows of anchor bolt holes; two anchor drill rigs 213 are provided before and after the loading platform.

[0050] In this embodiment, the translation telescopic arm is connected to a four-bar linkage 208, and the four-bar linkage 208 adopts a translation mechanism. The translation telescopic arm can make the advance support platform 1 move up and down through the four-bar linkage 208, and can make the advance support platform 1 move forward and backward through the translation telescopic arm, so as to meet the undulation of the roof along the coal seam and closely support the roof of the tunnel, and the lifting force is about 6 tons; the first spiral swing cylinder 209 is horizontally arranged, which can make the advance support platform 1 axially deflect on both sides to adapt to different tunnel roofs, and the second spiral swing cylinder 210 is vertically arranged, and the bottom end of the second spiral swing cylinder 210 is connected to the second end of the first spiral swing cylinder 209, which can make the advance support platform 1 rotate horizontally to adjust the relative position of the advance support platform 1.

[0051] In this embodiment, the four-bar linkage 208 includes two groups of connecting rods, each group of connecting rods includes two connecting rods arranged in parallel, one end of one group of connecting rods is rotationally connected to the bottom of the translation telescopic arm, and the other end is connected to the gantry telescopic beam 206, one end of the translation telescopic arm is rotationally connected to the gantry telescopic beam 206, and the other end is rotationally connected to the mounting seat of the first spiral swing cylinder 209, and the first spiral swing cylinder 209 is rotationally installed on the mounting seat; one end of the other group of connecting rods is rotationally connected to the top of the translation telescopic arm, and the other end is rotationally connected to the mounting seat of the first spiral swing cylinder 209.

[0052] In this embodiment, a pressure sensor 211 is installed on the top of the second spiral swing cylinder 210, and the mounting seat 212 is installed on the pressure sensor 211. The pressure sensor 211 can detect the pressure change of the tunnel roof and digitally display the force condition of the platform.

[0053] In this embodiment, a driver's seat 216 is installed on the gantry telescopic beam 206, and the operator can remotely control the cutting of the tunnel boring machine, and the driver has a wide operating field of vision; a water and gas exploration drill arm can also be optionally installed on the gantry telescopic beam 206.

[0054] In this embodiment, the advance support platform 1 includes a cross beam assembly 102, a longitudinal beam assembly 103, a left support frame assembly 104 and a right support frame assembly 101. The longitudinal beam assembly 103, the left support frame assembly 104 and the right support frame assembly 101 are all installed on the cross beam assembly 102. The left support frame assembly 104 and the right support frame assembly 101 are respectively installed on both sides of the cross beam assembly 102. A plurality of longitudinal beam assemblies 103 are installed on the cross beam assembly 102; wherein, the longitudinal beam assembly 103 adopts a telescopic longitudinal beam, and its fixed part can be installed with a support plate as a fixed platform, and its telescopic part can be installed with a support plate as a movable platform when it is extended; and the cross beam assembly 102 can also be telescopic, and the position of the longitudinal beam assembly 103 on the cross beam assembly 102 is adjustable. Alternatively, the specific structure of the advance support platform 1 can be adjusted according to work needs.

[0055] This embodiment is efficient in changing "long-time empty top" to "instant empty top", and changing "short digging and short branch" to "long digging and long branch"; it is also more intelligent, with separation of digging and anchoring, synchronization of digging and supporting, digital signals, data interaction, automatic control, and remote operation.

[0056] The working process of the advance support platform 1 in this embodiment is as follows:

[0057] 1. The roof condition is poor, changing from "1 row" to "2 rows", that is, 1 row of fixed platform, 1 row of movable platform, and two outriggers at the head, the production efficiency is increased by 100%;

[0058] Second, the roof condition is good. The original cutting "2 rows" is changed to "3 rows", that is, 2 rows of fixed platforms and 1 row of movable platforms. Two legs are dropped at the head. If the pressure sensor 211 is stressed, 2 legs under the main beam of the supporting platform are dropped, a total of 4 legs are dropped. If it is not accepted, 2 legs are dropped, and the production efficiency is increased by 50%;

[0059] 3. The top plate condition is good. Originally, it could cut more than "2 rows". After using this folding platform, the fixed platform becomes "3 rows" and the movable platform becomes 2 rows. Depending on the stress condition of the top plate, in addition to the two front legs, the fixed platform is equipped with 2 to 4 legs, which is determined according to the stress condition of the sensor. The production efficiency is increased by 60%.

[0060] The specific application of the advanced support monorail hydraulic anchor drilling vehicle in this embodiment is as follows: Figure 10-13 shown.

[0061] In this embodiment, the reliability of the advance support is ensured. The advance support platform 1 senses the change of the tunnel roof through the pressure sensor 211, and drops the two legs on the fixed platform to automatically support the tunnel roof (apply force). As the tunnel boring machine cuts and advances, the movable platform slides forward as the tunnel boring machine cuts deeper. After the last row of cutting is completed, the tunnel boring machine retreats from the working surface, and the folding platform under the movable platform extends forward 180 degrees, quickly pressing against the roof just cut by the tunnel boring machine, dropping the two front legs, and opening the front guard plate to prevent spalling, thereby improving the safety of the working environment.

[0062] The operation of this embodiment is simple. By starting the sequence keys on the remote control valve group, the airborne platform 202 first slides forward on the main frame 201. After sliding into place, the airborne platform 202 and the front legs 204 and the rear legs 205 of the airborne platform are dropped to stabilize the airborne platform 202 and calibrate the level; secondly, the anchor drill rig 213 slides out from the airborne platform telescopic arm 203 on the airborne platform 202 to the advance support platform 1 and erects the vertical airborne platform 202, and stops when the telescopic arm reaches the first row of anchor operation positions; finally, multiple anchor drill rigs 213 align with the steel belt holes to drill the anchor holes on the first row of top plates, and complete the top plate in the assigned operation area, and the two gangs perform their own anchor and cable operations.

[0063] In this embodiment, the labor intensity of workers is reduced. The track beam is equipped with a rail remover, which enables the equipment to have an automatic rail removal function. The track can be automatically removed and installed with manual assistance. The specific structure of the rail remover is set according to work needs; the track beam is also equipped with a 5-ton hydraulic hoist, and auxiliary materials within 200 meters can be transported to the working surface by themselves;

[0064] This embodiment improves the support efficiency. The anchor drill is designed with a fine-tuning mechanism to accurately and quickly find holes and align them. The anchor machine has a large torque and can automatically lock the anchor tray nuts. The number is large. A double-slide rotation mechanism is designed to achieve 360-degree rotation of the anchor cable vertically on the top and side bottom plates, and can hit the bottom anchor cables on both sides.

[0065] Specifically, the anchor drilling rig includes: a swing seat assembly, a primary slide assembly, a secondary slide assembly, a primary slide compensation cylinder and various pins, etc.;

[0066] The swing seat assembly is installed on the telescopic drilling arm platform, including: a fixed swing seat, a movable swing seat, a swing cylinder, a slider and various pins, etc. By controlling the extension and retraction of the swing cylinder, the movable swing seat can be driven to swing left and right;

[0067] The primary carriage assembly is installed on the swing seat assembly, including: slide rails, cylinder seat, primary carriage propulsion cylinder, propulsion chain assembly, slide plate assembly, slewing drive and various pins, etc. By controlling the extension and retraction of the primary carriage propulsion cylinder, the propulsion chain assembly can be driven to move forward and backward, thereby driving the slewing drive to move forward and backward. The slewing drive is connected to the slewing seat of the secondary carriage assembly. The slewing drive, also called a slewing reducer, can make the secondary carriage assembly rotate 360°.

[0068] The secondary slide assembly is installed on the rotary drive of the primary slide assembly, including: slide rails, return cylinder seat, secondary slide compensation cylinder, propulsion cylinder, propulsion chain assembly, seat plate assembly, propeller assembly, vise assembly, slider and various pins, etc. By controlling the extension and contraction of the propulsion cylinder, the propulsion chain assembly can be driven to move forward and backward, thereby driving the propulsion assembly to move forward and backward. By controlling the extension and contraction of the secondary slide compensation cylinder, the secondary slide assembly can be driven to move forward and backward.

[0069] One end of the first-stage slide compensation cylinder is connected to the hinged seat of the swing seat assembly, and the other end is connected to the cylinder seat of the first-stage slide assembly. By controlling the extension and retraction of the first-stage slide cylinder, the first-stage slide assembly can be driven to move forward and backward.

[0070] The support platform in this embodiment is designed to meet various roof conditions such as slope changes along the coal seam tunnel roof, trapezoidal, arched and rectangular, and the climbing ability reaches ±18 degrees to meet the needs of tunnel slope changes. The support platform is designed with steel belt and steel mesh positioning holes, which can rotate horizontally and fine-tune the steel belt vertically on both sides of the tunnel, with a high degree of automation.

[0071] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An advanced support monorail hydraulic anchor drilling vehicle, characterized in that: The invention comprises an anchor drilling vehicle body and an advance support platform, wherein the anchor drilling vehicle body comprises a main frame, an airborne platform and a power station assembly, wherein the power station assembly is installed at the rear end of the main frame, a gantry telescopic beam is arranged at the front end of the main frame, gantry legs are arranged at the bottom of both ends of the gantry telescopic beam, and a main frame rear leg is also arranged at the rear end of the main frame, and the main frame rear leg can support the tunnel roof; a translation telescopic arm is installed on the gantry telescopic beam, the translation telescopic arm is connected to a first spiral swing oil cylinder, the first spiral swing oil cylinder is connected to a second spiral swing oil cylinder, and a mounting seat that can be connected to the advance support platform is installed on the second spiral swing oil cylinder; the airborne platform is installed on the main frame and can move along the main frame, and an anchor drilling rig is installed on the airborne platform; The airborne platform is connected to the main frame through a wing-type arm, front legs of the airborne platform are installed on both sides of the front end of the airborne platform, and rear legs of the airborne platform are installed on both sides of the rear end of the airborne platform. The airborne platform is provided with an airborne platform telescopic arm, and the airborne platform telescopic arm is connected to the anchor drilling rig; The translation telescopic arm is connected to the first end of the first spiral swing oil cylinder through a four-bar linkage, and the first spiral swing oil cylinder is arranged horizontally; the second spiral swing oil cylinder is arranged vertically, and the bottom end of the second spiral swing oil cylinder is connected to the second end of the first spiral swing oil cylinder; The advanced support platform comprises a crossbeam assembly, a longitudinal beam assembly, a left support frame assembly and a right support frame assembly, and the longitudinal beam assembly, the left support frame assembly and the right support frame assembly are all installed on the crossbeam assembly.

2. The advance support monorail hydraulic anchor drilling vehicle according to claim 1 is characterized in that: The main frame and the power station assembly are both equipped with driven wheels, and the driven wheels can be installed on a track beam, and the track beam is installed on the top plate of the tunnel.

3. The advance support monorail hydraulic anchor drilling vehicle according to claim 2 is characterized in that: The power station assembly includes a hydraulic system, an electrical system and a drive assembly, and the drive assembly is connected to the main frame; the drive assembly is equipped with drive wheels, and the drive wheels are installed on both sides of the track beam.

4. The advance support monorail hydraulic anchor drilling vehicle according to claim 2 is characterized in that: A hydraulic lifting hoist is installed on the track beam, and the track beam is equipped with a track remover.

5. The advance support monorail hydraulic anchor drilling vehicle according to claim 1 is characterized in that: A pressure sensor is installed on the top of the second spiral swing cylinder, and the mounting seat is installed on the pressure sensor.

6. The advance support monorail hydraulic anchor drilling vehicle according to claim 1, characterized in that: A driver's seat is installed on the gantry telescopic crossbeam.

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