Title:
LEVEL MEANS
United States Patent 3638535


Abstract:
A system for raising and lowering a platen, which is hinged along one edge, by a plurality of rams which have their piston rods pivoted adjacent to the opposite edge of the platen while maintaining the platen in a substantially level condition even if the platen is unequally loaded. The system includes a master ram and a plurality of slave rams. The master ram is operated in response to a command signal which is modulated by an error correcting feedback signal. The feedback signal is generated by an angular position-sensing potentiometer. The slave rams are operated in response to a signal generated in response to transient fluid pressures developed in the master ram so that the slave rams all attain the same pressure as that present in the master ram. A level-comparing device is provided which compares the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand. A signal is generated in response to any difference in the level of the slave rams and this signal is employed to correct and modulate the signal generated in response to pressure in the master ram.



Inventors:
PONTER ROBERT J
Application Number:
05/077057
Publication Date:
02/01/1972
Filing Date:
10/01/1970
Assignee:
RITTER ENGINEERING CO.
Primary Class:
Other Classes:
91/512, 91/522, 91/523
International Classes:
F15B11/22; (IPC1-7): F15B11/22
Field of Search:
91/411R,411B,412 60
View Patent Images:



Primary Examiner:
Geoghegan, Edgar W.
Claims:
What is claimed is

1. A platen raising, lowering, and leveling system comprising a platen, ram means for positioning said platen at a preselected position, said ram means including master ram means and slave ram means, valve means associated with each ram means to admit and exhaust fluid pressure to and from each ram means, control means for each valve means, means to generate one of a multiplicity of command signals to the control means associated with he valve means controlling said master ram means, said control means, in response to a command signal, operating said master ram valve means until said master ram means attains a desired position corresponding to the value of said command signal, position sensing means associated with said platen to determine the actual position of said platen, means responsive to said position-sensing means to generate an error-correcting signal to the control means associated with the valve means controlling said master rams means said associated control means operating its valve to correct any error in the position of the master ram signal-generating means responsive to the pressure in said master ram and adapted to transmit a signal to each other control means as a function of the fluid pressure in the master ram means, each of said other control means operating its valve means in response to said signal so that each slave ram means attains a pressure corresponding to the pressure of said master ram means, means to compare any difference in the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand, means for generating an error-correcting signal as a function of any level differences between said slave rams, and means for feeding the error-correcting signal to said other control means to modulate and correct the signal transmitted to said other control means from the pressure-responsive signal-generating means.

2. A platen raising, lowering, and leveling system comprising an assembly platen and a support platen, said platens being hinged together along one edge, ram means for each platen having piston rods pivoted adjacent the opposite edge of each platen and adapted to pivot each platen between substantially horizontal and substantially vertical positions, said ram means including master ram means and slave ram means, valve means associated with each ram means to admit and exhaust fluid pressure to and from each ram means, control means for each valve means, means to generate one of a multiplicity of command signals to the control means associated with the valve controlling said master ram means, said control means in response to a command signal operating said master ram valve means until said master ram means attains a desired position corresponding to the value of said command signal, position-sensing means associated with each of said platens to determine the actual positions of said platens, means responsive to said position-sensing means to generate an error-correcting signal to the control means associated with the valve controlling said master ram means, said associated control means operating its valve to correct any error in the position of the master ram means, signal-generating means responsive to the pressures in said master ram means and adapted to transmit a signal to each other control means as a function of the fluid pressure in the master ram means, each of said other control means operating its valve means in response to said signal so that each slave ram means attains a pressure corresponding to the pressure of said master ram means, means to compare any differences in the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand, means for generating an error-correcting signal as a function of any level differences between said slave ram means, and means for feeding the error-correcting signal to said other control means to modulate and correct the signal transmitted to said other control means from the pressure-responsive signal-generating means.

3. A platen raising, lowering, and leveling system according to claim 1, wherein said means to compare any differences in the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand comprises a plurality of reservoir means connected together by fluid conduit means, each of said reservoir means having float means contained therein, each of said fluid reservoir means being pivotally connected to the platen adjacent one of the slave ram means, and wherein said means for generating an error-correcting signal as a function of any level differences between said slave ram means comprises rod means connected to each of said float means, coil means surrounding each rod means to generate said error-correcting signal as a function of any differences in level of said float means.

4. A platen raising, lowering, and leveling system according to claim 1, wherein said position-sensing means associated with said platen to determine the actual position of said platen comprises a gear segment fixed to said platen, spur gear means meshing with said segment gear, and wherein said means responsive to said position-sensing means includes an angular motion potentiometer driven by said spur gear which generates said error-correcting signal to the control means associated with the valve controlling said master ram means.

5. A platen raising, lowering, and leveling system comprising a platen, ram means for positioning said platen at a preselected position, said ram means including master ram means and slave ram means, means to admit and exhaust fluid pressure to and from each ram means, means to sense the fluid pressure in said master ram means and to provide that pressure in each of said slave ram means, means to compare any differences in the actual extended level of at least one slave ram on the one hand with the actual extended level of at least one other slave ram on the other hand, and means to correct any level differences between said slave rams.

Description:
This invention relates to platens having a raising and lowering system which maintains the platen in a level condition during such operations. This invention is particularly suitable for use in assembly operations wherein a structural section of an article is assembled in a horizontal position on an assembly platen. The assembly platen is hinged along one edge. After the component is assembled on the platen, a plurality of rams raise the opposite edge of the platen until the platen is in a substantially vertical position. During this operation the article is supported by a support platen which is pivoted to the hinge for the assembly platen. Rams on the opposite edge of the support platen permit the support platen to be lowered as the assembly platen is raised. In this manner, the assembled article is rotated through 90° so that it may be assembled or joined to previously assembled components. This operation is particularly useful in ship-building techniques wherein hull sections are assembled in a vertical position and then raised to a horizontal position so that the assembled hull section may be joined to the mail hull. It should be appreciated that while the hull section is raised to a horizontal position, it is imperative that the platen remain in a level position since any bending stresses in the hull section may cause weld breakage of cracking and may result in an imperfect fit between the hull section and the remainder of the hull.

This invention provides a system which maintains a level platen position during raising and lowering operations even under unequal loading conditions on the rams. According to this invention, a master ram is provided which is raised or lowered in response to a command signal. The command signal to the master ram is modulated and corrected by a feedback signal, which is generated by a position sensor, which may be a potentiometer that generates a linear signal in response to the angular position of the platen. The pressure in the master ram is sensed by a pressure transducer and the pressure transducer generates a signal to a plurality of slave rams. The slave rams are provided with a level-sensing device that compares the level of one or a group of slave rams on the one hand with the level of another or a group of slave rams on the other hand. A signal is generated in response to any difference in level between the slave rams and that signal corrects and modulates the signal generated by the pressure transducer. Thus, any unequal loading on the rams which would tend to generate a false pressure signal is corrected by the signal generated in response to the true level of the slave rams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a platen raising, lowering, and leveling system in accordance with this invention.

FIG. 2 is a diagrammatic illustration of the control system according to this invention.

FIG. 3 is a cross-sectional view of a leveling means employed in conjunction with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, an assembly platen 10 and a support platen 11 are illustrated in FIG. 1. The platens 10 and 11 are identical in construction and for purposes of simplicity and clarity, only the platen 10 will be described in detail. Furthermore, the platens 10 and 11 have identical raising and lowering systems and the system employed in conjunction with the platen 10 will be described in detail.

The platen 10 includes a plurality of support beams 12, 13, 14, 15, 16, 17, 18, 19, 20, and 21. The beams 12 through 21 are hinged at their lower ends to a shaft 22 for pivotal movement from a horizontal position through an angle of 90° to a vertical position. The beams 12 through 21 are joined together by cross beams 23 and carry an assembly platen bed 24.

For each beam 12 to 21, there is provided a ram 25, 26, 27, 28, 29, 30, 31, 32, 33, and 34, respectively. Each ram 25 to 34 has a piston rod 35 which is pivotally connected to a beam 12 to 21 by a pin 36. Each ram 29 has a cylinder base 37 pivoted in a trunnion 38.

Each ram 25 to 34 has a pressure chamber 39 (FIG. 2) which is supplied with fluid from a pressure source 40. Although the pressure source 40 is illustrated in FIG. 2 as separate units, it is to be understood that the source 40 may comprise a single source, such as a pump. The pressure fluid is admitted to and exhausted from each pressure chamber 39 by a line 41, and flow through the line 41 is governed by a four-way, closed center valve 42. Each valve 42 is operated by a control means 43 which operates its valve 42 to exhaust fluid from or to supply fluid to the pressure chamber 39 in response to a particular signal to the control means. Absence of a signal to the control means will maintain the valve 42 in its illustrated closed position. Each control means 43 receives a signal from its own servocontroller 44.

In the illustrated embodiment, the ram 29 comprises a master ram. As was previously indicated, the master ram 29 is pivoted to the beam 16. Also associated with the beam 16 is an angular motion sensor 45 which produces a linear voltage signal as a function of the actual angular position of the beam 16. The angular motion sensor 45 may comprise an angular motion potentiometer having a mechanical input signal which produces a corresponding linear output signal voltage. The mechanical input signal to the angular motion sensor comprises a segment gear 46 mounted on the beam 16 and a pinion gear 47 which engages the segment gear 46. Rotation of the pinion gear 47 produces an output signal from the potentiometer as a linear function of the angular displacement of the pinion gear 47. The output signal generated by the angular motion sensor is transmitted by a lead 48 to the servocontroller 44 associated with the master ram 29.

The valve 42 associated with the master ram 29 is operated in response to a signal generated by a command signal generator 49. The signal generated by the command signal generator is transmitted to the servocontroller and is compared to the signal generated by the angular motion sensor. Thus, the command signal is modulated and corrected by the signal generated by the angular motion sensor. If these signals match and cancel each other, the servocontroller has a zero output to the valve control means 43 and the valve 42 remains in its closed condition. If, however, the command signal exceeds the signal generated by the angular motion sensor, the valve 42 is shifted to admit fluid to the pressure chamber 39. If, on the other hand, the angular motion sensor senses an angular position exceeding that position determined by the command signal generator, a signal is transmitted to the valve control means 43 which shifts the valve 42 to a position which exhausts fluid from the pressure chamber 39. Thus, to raise the assembly platen to a predetermined position, a command signal is generated, and that signal has a value which corresponds to a value which is sufficient to operate the valve 42 so that the ram 29 attains a position corresponding to the predetermined position. Any error in this position is sensed by the angular motion sensor 45 and a signal is transmitted to the servocontroller 44 to correct any such error.

Pressure transducers 51, 52, 53, 54, 55, 56, 57, 58, 59, and 60 are respectively provided on the rams 25 to 34. These pressure transducers are associated with pressure cells which communicate with the pressure chambers 39 and include strain gauges which transmit a signal which is proportional to the amount of pressure in the pressure chambers 39. Signals produced by the pressure transducer 55 associated with the master ram 29 are transmitted by a lead 61 to the servocontrollers 44 other than the servocontroller 44 associated with the master ram 29.

Thus, as the master ram 29 is raised in the previously described manner, the pressure in the master ram 29 increases and the pressure transducer 55 associated with the master ram 29 transmits a command signal to each other servocontroller 44. In response to this command signal, each other controller 44 transmits a signal to each other valve operating means 43 to operate each other valve 42 to match the pressure in the slave rams 25-28 and 30-34 with that pressure obtained in the master ram 29. The pressure transducers 51-54 and 56-60 associated with the slave rams generate an error correcting signal which is fed back into the servocontroller 44 to modulate the signal received from the pressure transducer 55 associated with the master ram 29.

In the illustrated embodiment, the ram 30 is a slave ram with respect to the pressure in the master ram 29. The ram 30 may also serve as a backup ram in the system so that the ram 30 may become the master and the ram 29 may be slaved to the pressure in the ram 30. In this regard, it should be noted that the ram 30 is provided with an angular motion sensor 50 so that the control systems associated with the ram 30 duplicate those associated with the ram 29. To convert the ram 30 to a master ram and the ram 29 to a slave ram, the command signal generator 49 is connected to the servocontroller 44 associated with the ram 30 and disconnected from the servocontroller 44 associated with the ram 29. The signal generated by the pressure transducer 56 is transmitted to the servocontrollers 44 associated with the rams 25-29 and 31-34 and the signal generated by the pressure transducer 55 is transmitted only to the servocontroller 44 associated with the ram 29. These operations may be conveniently performed by suitable switch means (not shown).

As the master ram 29 is raised, the slave rams 25 to 28 and 30 to 34 are raised and the pressure in the slave rams corresponds to the pressure generated in the master ram. However, due to unequal loading conditions which may exist on the assembly platen, the platen may not be level even though equal pressures exist in all of the rams. To compensate for level errors among the slave rams therefor, a leveling means is provided.

The leveling means according to this invention includes level sensors 70, 71, 72, and 73 pivotally connected to the beams 15, 12, 18, and 21, respectively. Since the leveling sensors 70, 71, 72, and 73 are identical, only the sensor 71 will be described in detail.

Referring now to FIG. 3, the leveling sensor 71 includes a reservoir 74 which is in the form of a cup. The top of the reservoir 74 is closed by a neck 75 which is fixed to the open mouth of the reservoir 74 by capscrews 76. The reservoir 74 has a fitting 77 at its lower end and a manifold 78 is threaded into the fitting. The manifold 78 is in fluid communication with corresponding manifolds 79 (FIG. 1) provided on the leveling sensors 70, 72, and 73, respectively. Such fluid communication is provided by a common conduit 80.

The neck portion 75 is provided with an axial bore 81 and a threaded plug 82 having an axial bore 83 is provided at one end of the bore 81. The other end of the bore 81 is closed by a cap 84 and by a plug 85. The cap 84 has a cylindrical projection 86 which is pivotally attached to the beam 12 by a clevis 87 so that the leveling sensor 71 may be maintained in a vertical position by its weight for all platen positions.

A float 88 is provided in the reservoir 74. The float 88 has a weight 89 attached thereto so that the float is maintained in a vertical position. The upper end of the float 88 is provided with an axially projecting rod 90 having a soft iron rod 91 attached to its upper end. The soft iron rod 91 comprises the core of a linear variable differential transformer (LVDT), which includes the core 91 movable within the bore 81. Within the bore 81 and surrounding the core 91 there are provided windings 92 which include two identical secondary windings and a primary winding. As is conventional in linear variable differential transformers, when the core 91 is in a predetermined null position, the voltage output from the secondary windings are the same. When the core 91 is moved from its predetermined null position, however, the voltage output of one of the secondary windings increases and the voltage output of the other secondary windings decreases, depending upon the direction and extent of core movement.

Signals generated by the linear variable differential transformer associated with the leveling sensor 71 are transmitted to the servocontrollers 44 associated with the rams 25 and 26. Similarly, signals generated by the linear variable differential transformer associated with he leveling means 70 are transmitted to the servocontrollers 44 associated with the rams 27 and 28. Signals generated by the linear variable differential transformer associated with the leveling means 72 are transmitted to the servocontrollers 44 associated with the rams 31 and 32 and signals generated by the linear variable differential transformer associated with the leveling means 73 are transmitted to the servocontrollers 44 associated with the rams 33 and 34.

Each reservoir 74 is partially filled with a liquid 93 and the liquid in each reservoir 74 is in communication with the liquid in all other reservoirs through the manifolds 78 and 79 and the conduit 80 provided on the leveling means 70, 71, 72, and 73. When the fluid-connected leveling sensors are level with respect to each other, a float in one leveling sensor is at the same level as the float in the other leveling sensors. Thus, when the leveling sensors 70, 71, 72, and 73 are at the same elevation, the floats 88 in all of the leveling sensors are at the same level and the cores 91 all establish zero outputs for their associated linear variable differential transformers. If, however, a heavier load exists in the area supported by the rams 27 and 28, for example, and the remaining rams and the leveling sensors 71, 72, and 73 are slightly higher than the rams 27 and 28 and their leveling sensor 70 (even though equal pressures exist in all of the rams), the cores 91 in the leveling sensors 71, 72, and 73 will be retracted somewhat from their null position and the core associated with the leveling sensor 70 will be advanced somewhat from its null position. A signal will be transmitted by the linear variable differential transformer associated with the leveling sensors 71, 72, and 73 to the servocontrollers 44 associated with the rams 25, 26, 31, 32, 33, and 34 to modulate the output signal of the servocontrollers 44 to direct the valves 42 to exhaust fluid from the rams 25, 26, 31, 32, 33, and 34. Similarly, the signal generated by the linear variable differential transformer associated with the leveling sensor 70 will generate a signal directing the servocontrollers associated with the rams 27 and 28 to direct the valves 42 to add fluid to the rams 27 and 28 until the linear variable differential transformers again achieve a null position. It should be noted that the signals generated by the linear variable differential transformers override and correct the signal transmitted by the pressure transducer 55.

There is provided on each leveling sensor 70 to 73 a sight glass 100 so that visual observation may be made of the fluid in any sensor. Each sensor 70 to 73 is also provided with an overflow outlet and air vent 101 (FIG. 1) so that in the event that a sensor does not pivot properly, fluid will be dumped through the vent 101 rather than flowing into the primary and secondary coils of the linear variable differential transformers.

It should be appreciated that other linear or angular motion sensors may be employed in conjunction with this invention. For example, the linear motion sensors associated with the leveling sensors may be linear motion variable inductors or linear motion variable capacitors. Furthermore angular motion may be sensed by angular motion variable capacitors, rotary variable differential transformers, variable reluctance angular position transducers, or the like.