Abstract:
A device for transporting fluids, such as viscous adhesives and sealants. The device includes a cylinder which may be filled by a supply line and a movable piston within the cylinder for ejecting the fluid into a discharge line. The piston includes an axial fluid channel and can be moved by way of a piston rod which also includes an axial fluid channel. An inlet valve is positioned between the supply line and the cylinder and may be moved between open and closed positions for releasing or interrupting the supply the fluid from the supply line into the interior of the cylinder. The piston rod includes threading and this threading is engaged with corresponding threading on a rotatable and drivable drive element so that the piston may be moved by rotating the drive element within the cylinder.

Description:
This application claims the priority of German Patent Application No. 29902514.4 filed Feb. 15, 1999, the disclosure of which is hereby fully incorporated by reference herein. 
     1. Field of the Invention 
     The present invention pertains to a device for transporting fluids, especially viscous adhesive or sealing materials, with a supply line which can be connected to a source of fluid, a cylinder which can be filled with fluid by means of the supply line, and a movable piston inside the cylinder for ejecting fluid which is in the cylinder into a discharge line which communicates with the interior of the cylinder. The piston has an axial fluid channel and can be moved by means of a piston rod which has an axial fluid channel, with an inlet valve positioned between the supply line and the cylinder which can optionally be moved to open and closed positions to release or interrupt the supply of fluid from the supply line to the interior of the cylinder. 
     2. Background of the Invention 
     Known devices generally related to the present invention are used in order to transport adhesives or other fluids in measured quantities. One such device is known from the disclosed German patent application DE 42 11 370 A1. In the known transport device, a piston which is connected to a hollow tappet, having an axial channel which is connected to the cavity of the tappet, can be moved by means of a pneumatic or hydraulic drive cylinder inside a transport cylinder in such a way that fluid from the transport cylinder is ejected through the fluid channel formed in the piston and the hollow tappet and into a flexible line. The disadvantages here are the relatively long flow paths of the fluid through the piston, the hollow tappet and the hose. 
     In addition, only a relatively imprecisely measured quantity of fluid can be transported by means of the pneumatic drive cylinder. An additional disadvantage consists in the fact that the known transport device is a relatively large construction due to the pneumatic cylinder which drives the displacement piston. Furthermore, the transport of the fluid is subject to variations, since the gas in the pneumatic cylinder is compressible and there can therefore be variations in pressure in the pneumatic cylinder and uneven movement of the piston. 
     From the public application papers for 20 38 369, a cylinder pump is known which has a piston which can be moved in a cylinder by means of a piston rod, where one end of the piston rod has threading which engages a rotatable threaded sleeve in order to axially move the piston rod and thus the piston. A disadvantage of this device is that so-called dead spaces can occur in the cylinder chamber, in which fluid collects and is not ejected from the cylinder chamber over the period of several strokes of the piston. Furthermore, because of the dead spaces there can be unwanted temperature changes in the fluid, due to the fact that a quantity of fluid which is the first to be drawn into the cylinder cools down within the cylinder, and is not pressed out of the cylinder chamber until the end of the ejection stroke of the piston, whereas fluid which is last drawn into the cylinder is the first to be pressed out of the cylinder chamber again with the help of the piston. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the task of providing a device to transport the fluid which avoids the disadvantages of the state of technology and makes it possible to transport an exactly measured quantity of a fluid, having compact and simple construction, and which in particular makes it possible to transport small quantities of fluid. 
     The invention accomplishes this task by providing the fluid transport device with a threaded piston rod. The threading on the piston rod engages corresponding threading on a drive element which is mounted so that it can rotate and can be propelled in a rotating manner, so that the piston can be moved in a cylinder by means of rotating the drive element. 
     The advantages of the invention consist mainly in the fact that by means of the corresponding threading on the piston rod, which has an axial fluid channel, and the drive element, measured transport of fluid with very exactly adjustable transport flows is realized, and at the same time there is the guarantee that because of the fluid channels formed in both the piston and the piston rod it is possible to fill the interior of the cylinder through these interconnected fluid channels, so that a quantity of fluid which is the first to reach the interior of the cylinder, after flowing through the interior of the cylinder, is the first again to be ejected, without small or even larger quantities of fluid collecting in a dead space in the cylinder and remaining in the cylinder longer than other quantities of fluid (first-in-first-out principle). By means of the combination, in accordance with the invention, of a piston rod which can be propelled with the help of threads, and the piston rod which has a fluid channel and a piston which also has an axial fluid channel, a compact design is realized for the device. 
     In an especially preferred manner, the piston rod is designed as a hollow spindle with male threads, and the drive element is designed as a threaded sleeve with female threads, since in this manner the double function of the piston rod in the form of a hollow spindle which serves on the one hand as the supply line for feeding the fluid into the interior of the cylinder and on the other hand as a means of propulsion for moving or shifting the piston inside the cylinder in order to draw fluid into or press it out of the piston can be realized with an especially compact and simple design. 
     In a manner which is likewise preferred, the implementation variant just described is further advanced by having the threaded sleeve mounted in a fixed location by means of a roller bearing on a housing and propellable by means of an electric motor, and by having gears between the threaded sleeve and the electric motor. The threaded sleeve, which is engaged with the hollow spindle in order to move the threaded sleeve and the piston axially, is thereby permanently and precisely mounted, and because of the gearing it can be driven at relatively low rotational speed, depending on the desired quantity to be transported, so that the piston is shifted in the cylinder at relatively low speed, in order to be able to transport relatively small quantities. At the same time, because of the gears, which preferably provide for a reduction in the speed of the electric motor, when the rotary speed of the drive element is low a relatively high torque is guaranteed in the drive element, so that the piston is moved in the cylinder with a relatively high force, so that variations in transport quantity can largely be avoided even with highly viscous fluids. 
     A gear system of relatively simple and reliable design consists in a gearset with a toothed belt, which works together with a gear wheel which is coupled to the threaded sleeve and another gear wheel which is coupled to the drive shaft of the electric motor. 
     In an especially preferred manner there is provision for the fluid flow path between an end section of the hollow spindle at the opposite end from the piston and the supply line to be interruptible by means of the inlet valve, for the inlet valve to be movable together with the hollow spindle, and for the supply line to be in the form of a flexible hose. The inlet valve is moved to the open position in order to fill the interior of the cylinder, and in this position the piston is shifted in such a way that fluid flows into the interior of the cylinder through the hollow spindle and the fluid channel formed in the piston. After the piston has reached its end position, the inlet valve is closed, and in order to transport fluid the hollow spindle can now be moved together with the piston by rotating the drive element, with the effect that fluid is pressed from the interior of the cylinder into a discharge line, which is preferably connected directly to the cylinder. By means of the flexible hose, the movements of the hollow spindle and the inlet valve can be adjusted relative to a fixed fluid source without problem. 
     In accordance with an additional preferred variant form it is proposed that the hollow spindle be guided at its end opposite the piston, and if appropriate that the inlet valve be guided by means of a linear guide. By having the piston guided axially inside the cylinder, on the one hand, and having the hollow spindle guided by means of a linear guide on the other hand, the elements of the device which can be moved relative to a housing are guided reliably for the back-and-forth movement which is necessary for operation. At the same time, an anti-twist prevention is realized for the hollow spindle and the piston. In a purposeful and robust manner, the linear guide has two guide rods and several guide sleeves which slide on the guide rods. 
     In an additional alternative implementation form of the invention, the inlet valve can be activated pneumatically or magnetically, since for both of these variants only little design effort is necessary. In an especially preferred manner, the discharge line is connected directly to the interior of the cylinder, and connects downstream to the discharge line of a fluid applying device, so that a complete device for transporting and applying a fluid is realized which can be attached to a robot arm, so as to be able, for example, to apply adhesive to motor vehicle parts in the manufacture of automobiles. 
     Since heated adhesives and sealants may be processed in many industrial applications, in accordance with an additional refinement of the invention a heating system is provided to heat the cylinder, so that the adhesive or sealant is kept at a preset temperature, especially during intermittent operation with relatively long interruptions in transport. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below on the basis of a sample implementation of a device for transporting fluids according to the invention, with reference to the accompanying drawings. The illustrations show the following: 
     FIG. 1 illustrates a device in accordance with the invention, in a partially sectional view; 
     FIG. 2 is a side view of the device from FIG. 1; and 
     FIG. 3 is a top view of the device shown in FIGS.  1  and  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The device shown in FIGS. 1 to  3  is used to transport and then to apply viscous adhesive or sealing materials on surfaces of substrates such as body parts of motor vehicles, and consists essentially of a fluid transporting device  2  and a fluid application device  4  which is coupled thereto. The entire device is removably attached by means of an attaching element  6  to a robot arm (not shown) or a jig of a production facility, so that the fluid application device  4 , which has a discharge jet for delivering adhesive or sealant, can be positioned relative to the substrate and possibly moved. The fluid application device  4  also contains an electrically or pneumatically activated application valve (not shown), by means of which the fluid channel formed inside the fluid application device  4  can optionally be opened or interrupted. 
     The fluid transport device  2  has a supply line  10  in the form of a flexible and heatable hose, which can be connected to a fluid source (not shown), a cylinder  14  formed in a metal housing  12 , and a piston  16  which can move in the cylinder  14 . 
     The cylinder  14  formed on the housing  12  has an interior which is limited by a tube-like cylindrical sleeve  18  which is inserted into the housing  12 . Sleeve  18  is made of a wear-resistant metal. The piston  16  is sealed against the inner surface of the cylindrical sleeve  18  by means of appropriate seals. The piston  16  has a fluid channel  20  running in the axial direction, which expands like a funnel in its lower section, so that fluid flows into the interior of the cylinder beneath the piston  16  at a lower speed than the flow speed in the cylindrical section of the fluid channel  20 . The volume of the interior of the cylinder  14  is defined at any given time by the position of the piston  16  within the cylinder  14 . In FIG. 1 the piston  16  is located in its lower stop position, in which the interior space of the cylinder  14  below the piston  16  is minimal. 
     The interior space of the cylinder  14  below the piston  16  communicates directly with a discharge line  22  which is cylindrical in cross section, through which fluid can be introduced into the fluid application device  4 . Inside the fluid application device  4  there is a fluid channel (not shown), which leads from the discharge line  22  to the discharge jet  8 . 
     A piston rod  24  is designed in the form of a hollow spindle  25  with male threading, and has a fluid channel running in the axial direction which communicates with the fluid channel  20  of the piston  16 . At its lower end section on the end toward the piston  16 , the piston rod  24  is solidly connected to the piston  16 . The outside diameter of the piston rod is smaller than the inside diameter of the cylindrical sleeve  18 , so that there is no contact between the piston rod  24  and the cylindrical sleeve  18 . 
     On its upper end section, on the end away from the piston  16 , the piston rod  24  in the form of a hollow spindle  25  is connected to a housing  28 . The housing  28  contains a channel  30 , partially shown, which makes a connection between the supply line  10  in the form of a hose and the fluid channel  26  formed in the hollow spindle  25 . By means of an adapter  40 , there is a connecting channel between the supply line  10  and the channel  30  within the housing  28 . In addition, the housing  28  holds an inlet valve  32 , which is inserted into the channel  30  between the supply line  10  and the end section of the hollow spindle  25 . This inlet valve  32  can be moved optionally to an open or a closed position. The inlet valve  32  makes it possible to interrupt the feeding of fluid from the supply line  10  through the channel  30 , the fluid channel  26  inside the hollow spindle  25 , and through the fluid channel  20  of the piston  16  into the interior of the cylinder  14  beneath the piston  16 . In the open position the fluid channel or fluid flow path described above is released. The inlet valve  32  is activated pneumatically. 
     The housing  28 , which is made of a rigid material, preferably metal, the upper end section of the hollow spindle  25  which is rigidly connected to the housing  28 , and the inlet valve  32  are guided in a straight line by means of a linear guide  34 . The linear guide  34  has two glide rods  36  which are parallel to each other and [at some] spaced apart, and four guide sleeves  38  which slide on the guide rods  36 . Because of the attachment of the hollow spindle  25  to the linear-oriented housing  28 , the hollow spindle  25  together with the guidance implemented inside the cylinder  14  by the piston  16  is centered within the cylinder  14  and can carry out a linear up-and-down movement without being caused to rotate. 
     As FIG. 2 shows, on the end sections of the guide rods  36  there are electric switches  37  and  39  which supply an electrical signal when the upper and lower end positions of the spindle  24  and the piston  16  are reached, in order to switch off the electric motor  46 . These switches  37 ,  39  may switch the electric motor  46  off directly. 
     To move the piston rod  24  in the form of a hollow spindle  25 , together with the piston  16 , up and down, there is a drive  42  element which is mounted on the housing  12  in such a way that it can rotate. This drive element  42  has female threading which engages the male threads of the piston rod  24 , which is in the form of a hollow spindle  25 . The drive element  42  is designed as a threaded sleeve, and is mounted to the housing  12  by means of a roller bearing  44 . By rotating the drive element  42 , and because of the engagement with the hollow spindle  25 , it exerts an axial force on the latter in an upward or downward direction, depending on the direction of rotation, which leads to an upward or downward movement of the piston  16  inside the cylinder  14  and thus either to ejection of fluid from or intake into the interior of the cylinder  14 . 
     The drive element  42  is driven by means of an electric motor  46  and an intermediate gearset  48 . The gearset  48  has a first gear wheel  50  which is coupled to the driveshaft of the electric motor  46 , a second gear wheel  52  which is coaxial to the hollow spindle  25 , and a toothed belt  54  which passes around both gear wheels  50 ,  52 . The gear wheel  52 , which can thus be turned by the electric motor  46 , is coupled to the drive element  42  by means of two connecting disks  56 ,  58 . 
     The electric motor  48  is coupled to a sensor  47  for the angle of rotation, which supplies information about the present angle of rotation, speed of rotation and direction of rotation of the driveshaft of the electric motor and the spindle  25 , and thus about the position, speed and direction of movement of the piston  16 , and ultimately about the quantity of fluid being transported. The rotational angle sensor  47  is of high resolution, so that the information mentioned above is very exact. 
     An electric heater  60  with a resistance heating element is placed around the portion of the housing  12  which forms the cylinder  14 , in order to heat the cylinder  14 . The heater  60  is controlled by a controlling and regulating unit, which is not shown. 
     To fill the interior of the cylinder  14 , the inlet valve  32  is first moved to its open position by means of the controlling and regulating unit. At the same time, the application valve for the fluid application device  4  is moved to the closed position. Immediately thereafter, the electric motor  46  is switched on, so that gear wheel  50  and gear wheel  52  are turned, the latter at a reduced speed which corresponds to the translation ratio compared to gear  50 . Together with gear wheel  52 , the drive element  42  is rotated. Because the female threads of the drive element  42  engage the male threads of the piston rod  24  in the form of a hollow spindle  25 , the piston  16  is moved upward from its lower stop position, shown in FIG. 1, in the direction of its upper stop position. At the same time the hollow spindle  25 , the housing  28 , the inlet valve  32 , the adapter  40  and the lower section of the supply line  10  in the form of a hose are moved upward translationally. During the upward movement, fluid such as adhesive or sealant is transported through the hose, the adapter  40 , the channel  30 , the inlet valve  32 , which is in the open position, through the axial fluid channel  26  formed in the piston rod  24  and the axial fluid channel  20  formed in the piston  16 , into the interior space of the piston  16  beneath the cylinder. 
     When the piston  16  has reached its upper stop position, the drive motor  46  is switched off automatically by activating the electric switch  37 , so that the movement of the piston  16  and the piston rod  24  is interrupted. 
     To transport fluid from the fluid transporting device  2  through the discharge line  22  to the fluid application device  4 , the electric motor  46  is switched on in the direction opposite to the direction for filling the cylinder  14 , so that the drive element  42  is now rotated in the opposite direction by means of the gearset  48 , so that the hollow spindle  25  together with the piston  16  in FIG. 1 is moved downward within the cylinder  14 , so that fluid which is beneath the piston  16  is transported through the discharge line  22  into the fluid application device  4 . The inlet valve  32  is in the closed position while the piston  16  is moving downward. By means of the fluid application device  4 , the adhesive can be applied to a substrate through the discharge jet  8 , possibly by means of pressurized gas. The fluid application device  4  is used either for simple application of fluid, or possibly for applying fluid under the effect of a flow of pressurized gas on the fluid (such as rotary spraying). When the piston  16  reaches its lower stop position, the electric motor  46  is switched off by activating the switch  39 . The fluid transport device  2  is then ready for another filling procedure as described above, to fill the interior of the cylinder  14  with adhesive. 
     The piston rod  24  in the form of a hollow spindle  25  has a dual function. On the one hand, fluid is conducted through the hollow spindle  25  from the supply line  10  into the interior of the cylinder  14 . On the other hand, the hollow spindle  25  serves for propulsion, that is, to shift the piston  16  axially within the cylinder  14 . This gives the device according to the invention a very compact design, and permits precisely measured transport of the fluid. The transport stream can be regulated precisely by adjusting the speed of the electric motor  46 , and depending on the translation ratio of the gearset  48  very slow displacement speeds of the piston  16  can be realized. The dwell time of fluid elements inside the cylinder  14  is very uniform, that is, the first fluid into cylinder  14  is the first fluid out of cylinder  14 . 
     While the present invention has been illustrated by a description of a preferred embodiment and while this embodiment has been described in some detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known.