Of Advancing Material Handling Means Or Roof Support Patents (Class 299/1.7)
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Patent number: 11746655Abstract: The present invention pertains to a method for monitoring operation of a mining machine unit, particularly of a longwall mining system, having a shield unit connected to a material removing unit by means of an actuator for adjusting a distance between the shield unit and the material removing unit, the method comprises the steps of determining a position change of the shield unit during an actuating operation of the actuator; and a step of detecting a malfunction of the mining machine unit based on the determined position change.Type: GrantFiled: March 2, 2020Date of Patent: September 5, 2023Assignee: Caterpillar Inc.Inventors: Euan Kirkhope, Johannes Wesselmann
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Patent number: 11459887Abstract: A system for navigation detection and inclination measurement of advanced hydraulic supports, including a detection device module, a signal transfer transmission module, connected to the detection device module, and used to integrate ultrasonic signals and inclination signals received from all advanced hydraulic supports and then wirelessly transmit all the signals to an analysis and processing module. The analysis and processing module, connected to the signal transfer transmission module, and used to receive the signals from the signal integration and transmission device for analysis, where if an analysis result shows an abnormal situation, an alarm will b e immediately given to a worker. If the analysis result shows a continuous abnormal situation, or a relatively large value indicating the abnormal situation is generated, a command will be immediately sent to make the advanced hydraulic supports stop operating in a current mode.Type: GrantFiled: December 31, 2020Date of Patent: October 4, 2022Assignees: Shandong University of Science and Technology, Tiandi Science & Technology Co., Ltd.Inventors: Yuxia Li, Kun Zhang, Liangsong Huang, Yajun Xu, Ying Ma, Desheng Zhang, Shaoan Sun, Jinpeng Su, Hongyue Chen, Si Wu, Zengkai Liu
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Patent number: 10655467Abstract: A method for implementing a centralized control platform of a hydraulic support on a fully mechanized mining working face in underground coal mines, which is used for safety production in the underground coal mines.Type: GrantFiled: January 12, 2018Date of Patent: May 19, 2020Assignee: Taiyuan University of TechnologyInventors: Muqin Tian, Chunyu Xu, Jiancheng Song, Wen Chai, Long Zhao
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Patent number: 10364676Abstract: Systems and methods are described for monitoring a condition of a mine roof using a longwall mining system. A plurality of powered roof supports is controlled to apply an adjustable support pressure on a mine roof. A condition of the mine roof is monitored based on the adjustable support pressure applied to the roof by a respective actuator of each powered roof support. In some implementations, the condition of the mine roof is monitored by generating and analyzing a graphical pressure map based on the adjustable support pressure applied by each powered roof support and a relative position of a shearer moving across the mine face. In some implementations, roof collapse events are detected based on temporally similar changes in the adjustable support pressure applied by multiple adjacent powered roof supports as indicated by the graphical pressure map.Type: GrantFiled: June 15, 2016Date of Patent: July 30, 2019Assignee: Joy Global Underground Mining LLCInventor: Jason Knuth
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Patent number: 10208592Abstract: A method of controlling a longwall mining system, the longwall mining system including a longwall shearer, a conveyor, and a plurality of roof supports, such that the method includes creating, by a controller, a load profile of the conveyor representing a distribution of mineral along a length of the conveyor, calculating, by the controller, a desired change in the load profile based on the load profile of the conveyor, and controlling, by the controller, the longwall mining system to adjust the distribution of mineral on the conveyor based on the desired change in load profile.Type: GrantFiled: December 2, 2015Date of Patent: February 19, 2019Assignee: Joy Global Underground Mining LLCInventor: Gareth Rimmington
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Publication number: 20150069814Abstract: A face equipment for mechanical extraction in longwall mining, in particular in the underground hard coal mining industry, includes a face conveyor (21) arranged along the coal face, an extraction mechanism (22) that can be moved along the face conveyor (21), and shield support frames (10) fastened at an angle to the face conveyor (21). In order determine the shield height of the extended shield support frame (10) corresponding to the face opening height, a flexible hose level (17) with a liquid-filled hose (18) is installed between the roof canopy (13) and floor skid (11) of individual shield support frames (10), and a pressure sensor (19) is arranged on the skid-side end of the hose (18). An inclination measuring device (25) is arranged on the roof canopy (13), and the pressure sensor (19) and inclination measuring device (25) are connected to an analyzing and control unit.Type: ApplicationFiled: April 2, 2012Publication date: March 12, 2015Applicant: RAG AKTIENGESELLSCHAFTInventors: Martin Junker, Armin Mozar
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FACE EQUIPMENT COMPRISING HOSE LEVELS PLACED BETWEEN THE FACE CONVEYOR AND THE SHIELD SUPPORT FRAMES
Publication number: 20150061352Abstract: A face equipment for mechanical extraction in longwall mining, in particular in the underground hard coal mining industry, includes a face conveyor (17) arranged along the mining wall, an extraction device (18) that can be moved along the face conveyor (17), and shield support frames (10) supported on the face conveyor (17) at an angle thereto. In order to determine the height of the face opening, a flexible hose level (21) with a liquid-filled hose (22) placed between the face conveyor (17) and at least one main component of the shield support frame (10) is installed in the area of the face conveyor (17). A pressure sensor (23, 24, 28) is arranged on at least one end of the hose (22). An inclination measuring device (25, 26) is arranged on the face conveyor (17) and on the main component of the shield support frame (10).Type: ApplicationFiled: April 2, 2012Publication date: March 5, 2015Applicant: RAG AKTIENGESELLSCHAFTInventors: Martin Junker, Armin Mozar -
Patent number: 8960807Abstract: A hydraulic circuit for longwall support for use in underground mining for supporting a longwall by means of a plurality of support shields incorporates a pressure monitoring device in the pressure line between the load maintaining valve and the shield control valve. The pressure monitoring device can be a device for monitoring the piston position of the shield control valve which device signals a deviation of the set position predetermined by the shield control device from the measured actual position of the piston of the shield control valve in the form of a deviation signal. It may also be a pressure sensor which signals the deviation of the set pressure predetermined by the shield control device from the measured actual pressure in the form of a deviation signal. Signaling can be acoustic or optical.Type: GrantFiled: June 18, 2010Date of Patent: February 24, 2015Assignee: Tiefenbach Control Systems GmbHInventors: Wilfried Weigel, Gerhard Wülfing, Peter Rahms
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Patent number: 8876218Abstract: A hydraulic circuit for longwall support for use in underground mining for supporting a longwall by means of a plurality of support shields includes in the annular piston line of each cylinder/piston unit a pressure sensor. The pressure sensor, upon reaching a predetermined maximum pressure activates a pressure deviation signal, causes the entire longwall to be depressurized by means of a longwall shut-off valve. The pressure deviation signal is blocked for one of the hydraulic valves against each triggering signal.Type: GrantFiled: March 15, 2012Date of Patent: November 4, 2014Assignee: Tiefenbach Control Systems GmbHInventors: Wilfried Weigel, Gerhard Wülfing, Peter Rahms
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Patent number: 8777325Abstract: A method and apparatus for determining the position and/or situation of installation components of a mineral mining installation which has as installation components at least one face conveyor for removing mined material, one shield-type support for keeping a face open, pushing devices for pushing the face conveyor and the shield-type support in active operation, an extracting machine which can be moved along the face conveyor, and a drift conveyor, the position and situation of at least one installation component being determined by a measuring system having a detection unit with measurement sensor and the detection unit decoupled from the movement of the extracting machine, can be or is moved to and fro between two points of the guiding system along at least one installation component at the face such as, e.g. the face conveyor, by a separate guiding system 21; a mining installation relating to the same.Type: GrantFiled: June 22, 2010Date of Patent: July 15, 2014Assignee: Caterpillar Global Mining Europe GmbHInventors: Johannes Wesselmann, Marco Ahler, Campbell Morrison
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Patent number: 8770373Abstract: A side shifting conveyor is provided for a surface mining operation. The conveyor generally includes conveyor sections and conveyor translation devices. Each conveyor translation device includes a drive operable to move the associated at least one conveyor section in a direction substantially perpendicular to the conveying direction. The conveyor further includes a controller operatively coupled to each drive for controlling operation of the drive and coordinating movement of the conveyor sections. A method for moving a conveyor in a surface mine generally includes sensing that a surface miner operable to deposit material onto the conveyor sections has moved beyond one of the conveyor sections, fixing a position relative to the surface mine of a conveyor translation device associated with one of the conveyor sections, and operating the conveyor translation device to move one of the conveyor sections in a direction substantially perpendicular to the conveying direction.Type: GrantFiled: April 15, 2011Date of Patent: July 8, 2014Assignee: Joy MM Delaware, Inc.Inventors: Brad Neilson, Michael S. Adamczyk, Joseph J. Zimmerman
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Patent number: 8708421Abstract: Method of automatically producing a defined face opening, in underground coal mining, during longwall mining operations having a face conveyor, a disk shearer loader and a hydraulic shield support. Via at least one inclination sensor on the top canopy of the shield support frame, the inclination of the top canopy relative to the horizontal, in the direction of mining or extraction of the disk shearer loader, is determined to provide angles of the course of an overlying stratum at the shield support frame. A stepping path length of each shield support frame is detected, and therefrom a cutting depth of the disk shearer loader during an extraction run is determined. A cutting height of the disk shearer loader is detected by means of sensors disposed thereon, and a cutting height of the disk shearer loader is adjusted in alignment with the angle of the course of the overlying stratum to produce the defined face opening.Type: GrantFiled: August 20, 2009Date of Patent: April 29, 2014Assignee: RAG AktiengesellschaftInventors: Martin Junker, Armin Mozar
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Patent number: 8672414Abstract: A method for controlling a longwall mining operation, including a face conveyor, at least one extraction machine, and a hydraulic shield support, in underground coal mining. Using inclination sensors disposed on at least three of the four main components of each shield support frame, such as floor skid, gob shield, support connection rods, and gob-side region of the top canopy, the inclination of the shield components relative to horizontal is ascertained in the direction of step. In a computer, the ascertained inclination data is compared with base data stored in the computer that defines the geometrical orientation of the components and their movement during stepping. From the comparison, a respective height of the shield support frame, at the forward end of the top canopy, is calculated as a measure for the face opening.Type: GrantFiled: February 19, 2008Date of Patent: March 18, 2014Assignee: RAG AktiengesellschaftInventors: Martin Junker, Armin Mozar
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Patent number: 8590982Abstract: A longwall mining system includes at least one face end roof support having a longitudinal length, and at least one near end roof support adjacent the face end roof support. The near end roof support has a longitudinal length substantially shorter than the face end roof support longitudinal length. There is also at least one face roof support adjacent the near end roof support, and the face roof support has a longitudinal length substantially shorter than the near end roof support longitudinal length. There is also a forward conveyor extending forward to and attached to the face end roof support, the at least one near end roof support, and the at least one face roof support, and a rearward conveyor extending rearward of and attached to the face end roof support, the at least one near end roof support, and the at least one face roof support.Type: GrantFiled: July 9, 2010Date of Patent: November 26, 2013Assignee: Joy MM Delaware, Inc.Inventor: John Holme
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Patent number: 8567869Abstract: The shield control device of a longwall shield for carrying out the longwall functions of the longwall shield in the longwall face working in a mine is associated with a distributing device upstream of a group of functional elements. Each of the functional elements of the longwall shield is associated with an exclusive address code word, on the call of which the internal connection between the shield control device and the functional elements depends. The distributing device is arranged in close proximity to the functional elements. The functional elements are valves or sensors.Type: GrantFiled: May 9, 2008Date of Patent: October 29, 2013Inventors: Willi Kussel, Peter Rahms
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Patent number: 8567871Abstract: A method for automatically producing a defined face opening in a longwall mining operation, in underground coal mining, having a face conveyor, at least one extraction machine and hydraulic shield support frames. Inclination sensors are disposed on at least three of the four main components of each shield support frame, such as floor skid, gob shield, support connection rods and gob-side area of the top canopy. From ascertained inclination data, by comparison with base data defining a geometrical orientation of the components and a movement thereof during stepping, a respective shield height of the shield support frames perpendicular to a bed thereof is calculated. From further sensors on the extraction machine, a cutting height thereof is acquired as a face opening.Type: GrantFiled: February 19, 2008Date of Patent: October 29, 2013Assignee: RAG AktiegesellschaftInventors: Martin Junker, Armin Mozar
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Patent number: 8567870Abstract: A method for maintaining, in a controlled manner, a top canopy/coal-face distance expedient for rock mechanics, in longwall mining operations in underground coal mining, using a face conveyor, at least one extraction machine, and a hydraulic shield support frame. Inclination sensors are disposed on at least three of the four main components of the shield support frame, including floor skid, gob shield, support connection rods and gob-side area of the top canopy. An inclination of the top canopy and floor skid are ascertained via the sensors. From the ascertained inclination data, in a computer, the effects on a top canopy/coal face distance are determined when changes in an angle of inclination of the top canopy occur. An automatic adjustment of decisive cycle parameters of the shield support frame are carried out, wherein the work cycle comprises retraction, advancement and setting processes.Type: GrantFiled: February 19, 2008Date of Patent: October 29, 2013Assignee: RAG AktiengesselschaftInventors: Martin Junker, Armin Mozar
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Publication number: 20130269453Abstract: A system for determining structural changes in a longwall mine, including a modulator wheel operatively coupled to a longwall mining machine, and a controller in communication with the modulator wheel; wherein the controller determines a movement of the longwall mining machine according to a signal received from the modulator wheel.Type: ApplicationFiled: March 26, 2013Publication date: October 17, 2013Inventor: Cut Coal Technology Holdings Pty Ltd
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Publication number: 20120161493Abstract: Method of automatically producing a defined face opening, in underground coal mining, during longwall mining operations having a face conveyor, a disk shearer loader and a hydraulic shield support. Via at least one inclination sensor on the top canopy of the shield support frame, the inclination of the top canopy relative to the horizontal, in the direction of mining or extraction of the disk shearer loader, is determined to provide angles of the course of an overlying stratum at the shield support frame. A stepping path length of each shield support frame is detected, and therefrom a cutting depth of the disk shearer loader during an extraction run is determined. A cutting height of the disk shearer loader is detected by means of sensors disposed thereon, and a cutting height of the disk shearer loader is adjusted in alignment with the angle of the course of the overlying stratum to produce the defined face opening.Type: ApplicationFiled: August 20, 2009Publication date: June 28, 2012Inventors: Martin Junker, Armin Mozar
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Publication number: 20120104829Abstract: A hydraulic circuit for longwall support for use in underground mining for supporting a longwall by means of a plurality of support shields comprises a pressure monitoring device in the pressure line between the load maintaining valve and the shield control valve. Said pressure monitoring device can be a device for monitoring the piston position of the shield control valve which device signals a deviation of the set position predetermined by the shield control device from the measured actual position of the piston of the shield control valve in the form of a deviation signal. It may also be a pressure sensor which signals the deviation of the set pressure predetermined by the shield control device from the measured actual pressure in the form of a deviation signal. Signaling can be acoustic or optical.Type: ApplicationFiled: June 18, 2010Publication date: May 3, 2012Applicant: Tiefenbach Control Systems GMBHInventors: Wilfried Weigel, Gerhard Wülfing, Peter Rahms
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Publication number: 20120098325Abstract: A method for automated production of a defined face opening in longwall mining operations in underground coal mining, comprising a face conveyor, disk shearer as extraction machine, and hydraulic shield support frame. At least one radar sensor is provided on a main body of the disk shearer. A distance between an upper edge of the main body and an underside of a top canopy of the shield support frame below which the main body travels during extraction work is measured, and is input into a computer as an actual value for a passage height of the disk shearer below the shield support frame. This actual value is compared with a target value and, if a deviation is determined, control commands are generated for adapting a cutting height of at least one of two cutting disks of the disk shearer.Type: ApplicationFiled: June 18, 2010Publication date: April 26, 2012Inventors: Martin Junker, Armin Mozar
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Publication number: 20110254346Abstract: A surface mining system for removing material from a mining face generally includes a conveyor extending substantially parallel to the mining face, a miner supported by and moveable along the conveyor, and a conveyor translation device associated with the conveyor and operable to move the conveyor and the miner toward the mining face. A method for advancing a surface mining longwall system generally includes moving the longwall shearer along a face conveyor, operating load translation devices to move the face conveyor and the longwall shearer toward the mining face, resetting a first group of load translation devices, and then resetting a second group of load translation devices. A load translation device generally includes an actuator, a ground drilling device coupled to and moveable with a portion of the actuator, and a frame coupled to and moveable with another portion of the actuator.Type: ApplicationFiled: April 15, 2011Publication date: October 20, 2011Inventors: Brad Neilson, Michael S. Adamczyk, Peter Dalton, Joseph J. Zimmerman
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Publication number: 20110049964Abstract: A method for controlling a longwall mining operation, including a face conveyor, at least one extraction machine, and a hydraulic shield support, in underground coal mining. Using inclination sensors disposed on at least three of the four main components of each shield support frame, such as floor skid, gob shield, support connection rods, and gob-side region of the top canopy, the inclination of the shield components relative to horizontal is ascertained in the direction of step. In a computer, the ascertained inclination data is compared with base data stored in the computer that defines the geometrical orientation of the components and their movement during stepping. From the comparison, a respective height of the shield support frame, at the forward end of the top canopy, is calculated as a measure for the face opening.Type: ApplicationFiled: February 19, 2008Publication date: March 3, 2011Applicant: RAG AktiengesellschaftInventors: Martin Junker, Armin Mozar
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Publication number: 20100320827Abstract: A method for maintaining, in a controlled manner, a top canopy/coal-face distance expedient for rock mechanics, in longwall mining operations in underground coal mining, using a face conveyor, at least one extraction machine, and a hydraulic shield support frame. Inclination sensors are disposed on at least three of the four main components of the shield support frame, including floor skid, gob shield, support connection rods and gob-side area of the top canopy. An inclination of the top canopy and floor skid are ascertained via the sensors. From the ascertained inclination data, in a computer, the effects on a top canopy/coal face distance are determined when changes in an angle of inclination of the top canopy occur. An automatic adjustment of decisive cycle parameters of the shield support frame are carried out, wherein the work cycle comprises retraction, advancement and setting processes.Type: ApplicationFiled: February 19, 2008Publication date: December 23, 2010Applicant: RAG AktiengesellschaftInventor: Martin Junker
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Patent number: 7549709Abstract: The invention relates to a mining device that is used at the face of a mine, said device comprising a sensor that is mounted on the planer for identifying the rock and transmitting rock data for no more than two measuring points per extraction unit via radio to each extraction control device. The measuring signals of adjacent measuring points are evaluated with respect to the prevalence of rock or coal. Based on said evaluation, the tilting unit that is common to the measuring points is controlled with regard to the raising or lowering of the planer. Each tilting unit is allocated an inclinometer, whose measured value of the inclination of the channel in the transversal direction of the latter is fed to the extraction control device and compared with the tilt signal that is generated by the evaluation. Each inclinometer is equipped with a radio transmitter for the radio transmission of the inclination signals to the assigned extraction control device.Type: GrantFiled: September 14, 2007Date of Patent: June 23, 2009Assignee: Tiefenbach Control Systems GmbHInventor: Willi Kussel
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Patent number: 7494190Abstract: A longwall support in a mine that comprises a plurality of longwall support units. The longwall support units are supported relative to a conveyor by stays that comprise cylinder-piston units. A control system with data acquisition, data storage, and programming is used to adapt the distribution of the staying forces over the length of the longwall, the sum of the staying forces acting upon the length of the longwall (total staying force), and the distribution of the advance forces over the length of the longwall continuously to the desired position of the conveyor. As a result, it is possible to influence the total staying force by the number of the stays with respect to an adjustable maximum, or the total staying force by controlling the longitudinal forces of the individual stays, or the total staying force as a function of at least one of the end positions of the conveyor.Type: GrantFiled: December 11, 2003Date of Patent: February 24, 2009Assignee: Tiefenbach Control Systems GmbHInventor: Willi Kussel
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Patent number: 7478884Abstract: A hydraulic switching mechanism for longwall supports. The present invention provides a hydraulic system that is controlled by its own pressure and may be adaptable to those currently in use so that life-threatening and costly faults cannot occur. With the present invention, the retrofitting of existing systems may be made possible without significant expenditure in modification.Type: GrantFiled: May 25, 2006Date of Patent: January 20, 2009Assignee: Tiefenbach Control Systems GmbHInventor: Willi Kussel
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Patent number: 7455367Abstract: A longwall support control for controlling the movements of longwall support units in the longwall of a mine that includes a central control system and a plurality of control units, of which a separate control unit (mining shield control device) is locally and operationally associated to each longwall support unit. The mining shield control devices connect to the central control system and to one another via two bus lines, through which each of the mining shield control devices can be called up for inputting a control command from the central control system or an adjacent mining shield control device. The identical second bus line (parallel bus) permits retransmitting to the adjacent mining shield control device, incoming signals that do not store a code word assigned to the respectively addressed mining shield control device.Type: GrantFiled: December 11, 2003Date of Patent: November 25, 2008Assignee: Tiefenbach Control Systems GmbHInventors: Ursula Kellermann, Christian Kellermann, Holger Kellermann
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Patent number: 7455368Abstract: A longwall support control for controlling the movements of the longwall support units and the advance heading in the longwall of a mine comprises a plurality of control units, of which a separate mining shield control device is locally and operationally associated to each longwall support unit. Each mining shield control device comprises a multi-channel radio transceiver, such that the mining shield control device is in a simultaneous transmit and receive mode with a decentralized operating device for receiving control signals and for transmitting inspection data. The mining shield control devices may be interconnected and each mining shield control device may include an amplifier.Type: GrantFiled: December 11, 2003Date of Patent: November 25, 2008Assignee: Tiefenbach Control Systems GmbHInventors: Willi Kussel, Peter Rahms
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Patent number: 7416369Abstract: A longwall support control for controlling the movements of longwall support units in the longwall of a mine that includes a central control system and a plurality of control units, of which a separate control unit (mining shield control device) is locally and operationally associated to each longwall support unit. Each mining shield control device comprises a switching element, which permits separating the bus line or lines in the mining shield control device. The mining control devices may also include signal amplifiers. An identical second bus line (parallel bus) permits retransmitting to the adjacent mining shield control device, incoming signals that do not store a code word assigned to the respectively addressed mining shield control device.Type: GrantFiled: December 11, 2003Date of Patent: August 26, 2008Assignee: Tiefenbach Control Systems GmbHInventors: Ursula Kellermann, Christian Kellermann, Holger Kellermann
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Patent number: 7076346Abstract: The present invention relates to an automated continuous haulage apparatus and method designed for use in underground environments. Each mobile bridge carrier (10) contains distance measurement (70) and angular position (74) means for determining the mobile bridge carrier's (10) position and the angular position of attached piggyback conveyors (30). Means for determining the ceiling height (76) are utilized to adjust the height of the piggyback conveyors (30). On each mobile bridge carrier (10), input from the various sensors is received by an electronic controller (80) that calculates the position and orientation of the bridge carrier (10) and attached piggyback conveyors (30). The controller then plans an optimal path of movement for the bridge carrier (10) and computes the rate of movement for each independently operated track assembly on the bridge carrier such that the bridge carrier (10) and piggyback conveyors (30) arrive as close as possible to the planned path.Type: GrantFiled: October 9, 2001Date of Patent: July 11, 2006Assignees: DBT America, Inc., Virginia Tech Intellectual Properties, Inc.Inventors: Robert H. Sturges, Michael Twigger, Amnart Kanarat
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Patent number: 6857705Abstract: A control system for a mining machine which moves in passes across a seam to be mined using absolute coordinates is disclosed. The machine is carried on rail and co-ordinates of the rail are measured along the length of rail. The rail is then moved to a new position for a next pass, and the distance of moving is determined from the co-ordinates previously measured. By knowing the co-ordinates, the rail can be moved to assume a desired profile, so that a desired profile of the seam can be achieved on the next pass. Co-ordinates of the up and down movement of a shearing head can also be measured and stored with the co-ordinates along the rail to provide a profile of the seam being cut, and so that on a next pass the intended position of the shearing head can be predicted and moved accordingly.Type: GrantFiled: April 23, 2001Date of Patent: February 22, 2005Assignee: Commonwealth Scientific and Industrial Research OrganizationInventors: David William Hainsworth, David Charles Reid
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Patent number: 6361119Abstract: A mining control system for adjusting the advance of the working tools of a mining machine with respect to working depth and/or working height connects to a detection device that is for recognizing the rock being mined and is carried along by the mining machine. A central command station connects by radio to the detection device of the mining machine. The mining control system comprises a plurality of radio receivers arranged in spaced relationship along the longwall, as well as a comparator, which is used for comparing the intensity of the radio signals received by the individual radio receivers and for retransmitting only the strongest of the radio signals to the central command station for generating the command signals for controlling the advance of the mining tools. It is also possible to transmit the radio signals received by each radio receiver to adjacent radio receivers. A separate comparator is associated to and controls each radio receiver.Type: GrantFiled: April 17, 2000Date of Patent: March 26, 2002Assignee: Tiefenbach Bergbautechnik GmbHInventor: Willy Kussel