DUAL-STATION TWO-LEG LOW-POSITION TOP COAL CAVING HYDRAULIC SUPPORT Technical Field The present utility model relates to a coal mine supporting device, especially to a dual-station 5 two-leg low-position top coal caving hydraulic support. Existing Technologies Support- and shield-type low-position top coal caving hydraulic support is the top coal caving hydraulic support mainly used for fully mechanized caving working face at present. There are mainly two structural forms: four-leg support- and shield-type low-position top coal 0 caving hydraulic support and two-leg support- and shield-type low-position top coal caving hydraulic support. The difference between them is that the former has two rows of legs (four in total), while the latter has only one row of legs (two in total), and forms stable mechanism through the equilibrium jack located between the upper beam and the shield beam. There are at least the following defects existing in four-leg support- and shield-type low-position 5 top coal caving hydraulic support in the prior art: The support has poor adaptability to broken surrounding rock, and the front & back row legs of the support is obviously under uneven distribution of force. Particularly, when top coal is broken, the resultant force application point of the support is generally located forward, with more force applied on the front legs and less force applied on the rear legs, which are even pulled. 0 There are at least the following defects existing in two-leg support- and shield-type low-position top coal caving hydraulic support in the prior art: The cutting off resistance at the rear of upper beam of the support is relatively weak, and has relatively poor adaptability to the top plate of complete top coal. Contents of the Utility Model 25 The object of the present utility model is to provide a dual-station two-leg low-position top coal caving hydraulic support, which has good adaptability to top coal. The object of the present utility model is realized by means of the following technical schemes: The dual-station two-leg low-position top coal caving hydraulic support of the present utility model comprises a base, an upper beam, a shield beam and a double-station equilibrium jack, , 30 characterized in that there are legs between the said base and upper beam, that the said upper beam is hinged with the said shield beam, that one end of the said double-station equilibrium jack is hinged with the said shield beam and the other end is hinged with the said upper beam at the first station and with the said base at the second station, and that hinge points are equipped on the said upper beam and base respectively. 35 According to the technical schemes provided by the present utility model as mentioned above and the description of the present utility model, hinge points are equipped on the said upper beam and base respectively, and one end of the double-station equilibrium jack is hinged with the shield beam; the other end can be hinged with either the upper beam or the base, and hinge points L are equipped on the upper beam and the base respectively. Different structural forms can be selected according to the conditions of top coal, with good adaptability to top coal. Description of Drawings FIG 1 is the structural schematic diagram of the dual-station two-leg low-position top coal caving 5 hydraulic support of the present utility model. Detailed Description of the Preferred Embodiments For the dual-station two-leg low-position top coal caving hydraulic support of the present utility model, the detailed preferred embodiments are shown in FIG 1. The hydraulic support comprises base 7, upper beam 1, shield beam 2 and double-station equilibrium jack 8, wherein leg 9 is 0 arranged between base 7 and upper beam 1, that two legs 9 can be arranged respectively at two sides of longitudinal center plane of upper beam I and base 7, and more legs 9 can also be arranged; upper beam 1 is hinged with shield beam 2, and one end of double-station equilibrium jack 8 is hinged with shield beam 2, and the other end can be hinged with either upper beam 1 at the first station or with base 7 at the second station; hinge points are equipped on upper beam 1 5 and base 7 respectively. Two double-station equilibrium jacks 8 can be arranged respectively at two sides of longitudinal center plane of shield beam 2 and base 7, or at two sides of longitudinal center plane of upper beam 1 and base 7. One double-station equilibrium jack 8 can also be arranged in the longitudinal center plane of 0 shield beam 2 and base 7, or in the longitudinal center plane of upper beam I and shield beam 2. For the dual-station two-leg low-position top coal caving hydraulic support of the present utility model, when double-station equilibrium jack 8 supports on upper beam 1, it is conducive for exploitation of fully mechanized caving working face of broken top coal; when double-station equilibrium jack 8 supports on base 7, it is conducive for exploitation of fully mechanized caving 5 working face of complete top coal. It can adapt to both top plate of complete top coal and top plate of broken top coal, improving the adaptability of the top coal caving support to different surrounding rocks and the support effects of fully mechanized caving working face, as well as meeting the requirements of fully mechanized caving exploitation with high production and high efficiency. 30 Detailed Embodiments: According to FIG 1, the dual-station two-leg low-position top coal caving hydraulic support mainly comprises upper beam 1, shield beam 2, front connecting rod 3, rear connecting rod 4, tail beam and spile coal caving mechanism 5, pusher jack 6, base 7, double-station equilibrium jack 8, leg 9, and face guard device 10, etc. 35 Upper beam 1 and base 6 are hinged and supported by two legs 9, and face guard device 10 is hinged with the front end of upper beam 1, and the rear end is hinged with shield beam 2; upper beam I or base 7 and shield beam 2 are hinged by double-station equilibrium jack 8, and the rear end of shield beam 2 is hinged with the tail beam and the tail beam jack of tail beam and spile coal caving mechanism 5. Front connecting rod 3 and rear connecting rod 4 are hinged between 40 shield beam 2 and base 7, forming stable four-connecting rod mechanism. Pusher jack 6 is arranged at the middle position of base 7. There are only two legs 9 in single row layout, and pedestrian passageways are provided at both front and back of leg 9. Single telescopic leg is employed for leg 9. The regular reliable structure is employed for the socket for hinging leg 9 with upper beam I and base 7, so as to meet the requirements of strengthen design. The overall semi-rigid structure is employed for base 7. Support-moving base lifting device for 5 can be arranged on base 7, so as to lift the front end of the base properly and have the support located on the bottom plate of the bench, or to lift the front end of the base and move it forward smoothly when the base is sunken. Pusher jack 6 is arranged at the middle position of base 7, and either of the following two structures can be employed for it: short pushrod structure of pusher jack installed in regular order 0 and long pushrod structure of pusher jack installed in reverse order. The two ends of pusher jack are connected with front conveyor and base 7 of the support respectively, so as to realize the function of pushing the hydraulic support and the conveyor forward. Face guard device 10, mainly comprising a face guard, a wall-protection jack, the corresponding connecting pieces and accessories, etc., is hinged with the front end of upper beam 1, and can 5 turn 1800 to make flushing and protect the top plate at front of the support. Either overall long upper beam or short upper beam with hinged front beam can be employed for upper beam 1. Upper beam 1 is equipped with movable side protection plate; when the protection plates at two sides of upper beam 1 are used, the plate at one side is fixed, and the one at the other side can be stretched, so as to seal the interstice of the support. The movable side protection 0 plate is hinged with the side pushing jack in beam body through a guide rod, and can realizes stretch through push of side pushing jack. Shield beam 2 is also equipped with movable side protection plate. The movable side protection plate structure of shield beam 2, is as same as that of the upper beam. The main functions of double-station equilibrium jack 8 are to adjust the angle of upper beam, 5 and make the hydraulic support adapting to different top plate conditions of coal through different connection positions as well as ensure reasonable strained condition of the hydraulic support. One or two double-station equilibrium jacks can be arranged according to the requirements. Front connecting rod 3 and rear connecting rod 4 are hinged between shield beam 2 and base 7, 30 forming four-connecting rod mechanism and stable mechanism of the hydraulic support. Wide connecting rod is employed for front connecting rod 3, and narrow connecting rod is employed for rear connecting rod 4. The four-connecting rod mechanism design with wide connecting rod at the front and narrow one at the rear, can increase the anti-torsion ability of the support, and ensure good stability and high reliability of the support, as well as a large equipment installation 35 & maintenance space at the rear of the support. Tail beam and spile coal caving mechanism 5, comprising a tail beam, a spile, a tail beam jack, a spile jack and the corresponding connecting pieces, etc., is mainly aimed to realize low-position top coal caving. The tail beam and the tail beam jack are hinged with shield beam 2 respectively, so that the tail beam can swing up and down; the spile is installed in the tail beam box body 40 through the spile jack, and the spile can be stretched out rearward and taken back from the rear of tail beam by means of the spile jack. The coal caving function can be realized through coordinated operation of the tail beam jack and the spile jack. The tail beam of tail beam and spile coal caving mechanism 5 can also be equipped with movable side protection plate according to the requirements, with plate structure and type similar to that of upper beam I and 15 shield beam 2.
Either large-flow manual control system or electric hydraulic control system can be employed for the dual-station two-leg low-position top coal caving hydraulic support. The support is provided with a spraying system for dust suppression. The foregoing description is just the detailed preferred embodiments to which, however, the 5 protection scope in the present utility model is not limited. Variations or alternatives which can be easily thought of by any technicians familiar with the technical field within the technical scope disclosed in the present utility model, shall be also covered by the protection scope of the present utility model. 0