Patent Publication Number: US-6655472-B1

Title: Device for producing an abrupt feed motion

Description:
The invention is based on a bolt pushing tool with which steel bolts can be inserted in hard material, e.g. concrete for fixing articles. The known bolt pushing tools make use of a propellant charge for producing the feeding or advance force, said charge being ignited and as a result of the explosive gases released a piston is driven. The piston then acts on the head of the bolt and pushes it out of the tool. 
     Numerous tools exist with which clips or nails are driven in. Such tools are known in the form of compressed air tackers or electrical tackers. However, these are not able to produce the characteristic force for bolt pushing tools. 
     The problem of the invention is to further improve a device for producing an abrupt or sudden feed motion with respect to the safety of handling. The device must e.g. be usable as a drive for a bolt pushing tool. 
     For solving this problem the invention proposes a device having the features of claim 1. Further developments of the invention form the subject matter of dependent claims, whose wording like that of the abstract is, by reference, made into part of the content of the description. 
     Whereas in the case of the known bolt pushing tools working always takes place with explosions, the device proposed by the invention can be operated with a motor drive, which has a lower safety risk. In addition, it is no longer necessary for the user to carry with him and store propellant charge magazines. The drive can e.g. be an electric motor, so that the tool can be operated and handled in the same way as a conventional portable drilling machine. The energy can be supplied by a battery. According to the invention the tool uses the motor drive in order to relatively slowly tension the striker spring. The completely tensioned spring is able to produce an adequately powerful feed or advance in order to e.g. drive a bolt with the same action into the substrate as in the case of the existing explosion-operated tools. 
     The feed device, which transfers the force of the relaxing spring, can e.g. have a push rod. This push rod can be guided in a corresponding guide and means can be provided in order to decelerate the end of the movement of the push rod if it has excessive energy. 
     According to a further development of the invention, the device also has a return mechanism for sliding back the feed device from the impact position into the starting position after performing the impact process. This ensures that the device automatically and rapidly returns to its starting position, so that it can be continuously used by a user. As the sliding back of the feed device can be carried out more slowly and with reduced force, the return mechanism can also be operated by the drive. However, it is also possible to give the return mechanism a spring. 
     It is particularly favourable if the spring element of the spring for performing the impact process and/or the spring element of the return spring is a pressurized gas. In this case the actual spring element has a negligibly low weight, so that the spring can very rapidly relax with a high force. 
     It can in particular be provided that the feed device has a piston on which the spring element directly acts. For example the push rod can be connected to a piston or constructed in one piece therewith and then the pressurized gas acts directly thereon. The push rod can also comprise several parts. 
     The piston can in particular be a double-acting piston on which the return spring acts directly. 
     According to a further development of the invention, the proposed device can have an axial piston guide. 
     The trigger for triggering the fitting or installation process can in particular have a valve, on whose operation the pressurized gas commences the impact process. 
     It can in particular be provided that the valve is opened for triggering the impact process. 
     The invention also proposes constructing the valve in such a way that it has a self-reinforcing opening movement. This ensures that the valve opens very rapidly as soon as it is triggered. 
     The invention proposes the spring-loading of the valve in the closed position. On triggering the insertion process it is consequently necessary to firstly overcome the spring tension with which the valve is urged into the closed position. This can be used for making the valve opening process jerky. 
     The trigger for triggering the insertion process can, according to the invention, be designed in such a way that it is triggered by the drive on reaching a specific position, which simplifies the handling of the tool. 
     It can be provided according to the invention that the striker spring is already pretensioned in the starting position of the feed device. 
     According to a further development of the invention the drive is constructed in such a way that during its operation, in order to initiate an impact process, the striker spring further tensions directly prior to triggering. Therefore the spring does not constantly have to be under maximum tension. 
     It is also possible to construct the drive in such a way that following the advance of the feed device the striker spring is temporarily further relaxed to facilitate its sliding back. 
     According to the invention the drive has a tubular element arranged coaxially to the piston guide and displaceable in the longitudinal direction of said piston guide. This makes the construction of the tool compact. Simultaneously the tubular element is guided on the piston guide. 
     For the displacement of the tubular element it is possible to place on an external thread of the bolt guide a rotatable nut, which during its use displaces by means of a bearing the tubular element. 
    
    
     Further features, details and advantages of the invention can be gathered from the following description of a preferred embodiment of the invention and the attached drawings, wherein show: 
     FIG. 1 A longitudinal section through an embodiment of a device proposed by the invention using the example of a bolt pushing tool. 
     FIG. 2 A partial section through the right-hand part of the bolt pushing tool in FIG. 1 in a second embodiment. 
    
    
     FIG. 1 diagrammatically shows a longitudinal section through a bolt pushing tool, which implements the invention. The bolt pushing tool contains an only diagrammatically represented casing  1 . The casing  1  has at its left-hand end in FIG. 1 a bore  2  permitting the introduction of a bolt to be fitted using said tool and from which it can be driven out again. The bore  2  is located in a leg  3  of the casing  1 . In the end of the bore  2  opposite to the left-hand end face  4  is inserted, preferably screwed a piston guide  5 , which is roughly tubular and contains in its interior a cylindrical channel  6  for the bolt to be fitted. On the end of the bolt guide  5  remote from the bore  2  is screwed a piston guide  7 , which contains a cylindrical cavity  8 , which is positioned coaxially to the cylindrical cavity  6  of the bolt guide. 
     The casing  1  contains a substantially cylindrical cavity  9 , which terminates at a certain distance upstream of the web  3 . Between the web  3  and a surface  10  of the casing  1  bounding the cavity  9  is provided a space through which a motor, which is not shown in the drawing and optionally having a trans-mission, can act on the tool. 
     In the cylindrical cavity  8  of the piston guide  7  is longitudinally displaceably guided a piston  11 , which is constructed in one piece at one end of a push rod  12 . The piston contains a groove  13  for housing a seal. With its free end  14  it engages on the shoulder, formed by a constriction, at the end of the piston guide  7 . The free end  15  of the push rod  12  remote from the piston  11  is located in the bolt guide  5  and is intended to act on the head of a bolt to be fitted. 
     In the cylindrical jacket of the piston guide  7  is provided an outwardly leading opening  16 . In the vicinity of said opening on the inside of the cavity  8  is formed an enlargement  17 . 
     A tubular element  18  is longitudinally displaceably mounted on the outside of the piston guide  7 . This tubular element  18  also has openings or perforations  19 , which permit a connection between the cavity  8  within the piston guide  7  and the cavity  9  of the casing  1 . These perforations are present at several points on the circumference of the tubular element  18 . 
     Over part of its length the outside of the bolt guide  5  is provided with an external thread  20 , which is intimated in the drawing. Onto the external thread  20  is screwed a nut  21 , which has a flange  22  located in a radial plane. Between the end face  23  of the flange  22  of the nut  21  facing the tubular element  8  and the latter is inserted a ball bearing  24 . Action can take place from the outside on the nut  21  through the drive in order to rotate or turn the same. During its rotation it simultaneously longitudinally slides the bolt guide  5  and this motion is transferred via the ball bearing  24  to the tubular element  18 . 
     From the side opposite to the web  3  a sleeve  25  is screwed into the cylindrical cavity  9  of the casing  1 . For reasons of simplification the drawing omits the seals between the sleeve  25  and the casing  1 . On its outwardly directed end the said sleeve  25  is closed in sealed manner by a disk  26 . The opposite, inner end of the sleeve  25  is coaxial to the tubular element  18 , which is sealed with the aid of a not shown seal with respect to the inside of the end of the sleeve  25 . Thus, the tubular element  18  is sealed both with respect to the outside of the piston guide  7  and with respect to the inside of the sleeve  25 . As a result the cavity  9  of the casing on the left-hand side of the sleeve  25  in FIG.  1  and the cavity of the sleeve  25  are separated from one another in sealed manner. 
     The disk  28  is centrally provided with a guide sleeve  27  screwed into it and projecting inwards into the sleeve  25  via the disk  26 . On said guide sleeve  27  is displaceably guided a-disk  28  sealed by not shown seals. The maximum displacement of the disk  28  is until it engages on a shoulder  29  on the inside of the sleeve  25 , as shown in FIG.  1 . In the reverse direction the disk  28  can be displaced until its end face  30  engages on the disk  26 . The space between the disk  28  and the disk  26  contains a pressurized gas, which is introduced into the space by means of an inlet  31  equipped with a valve. For simplification reasons the valve is not shown. The pressurized gas urges the disk  28  into the position shown. 
     In the interior of the guide sleeve  27  is displaceably guided a shaft  32  of a release valve  33 . In the position shown the shaft  32  is subject to the action of a compression spring  34 s. Sealing takes place between the shaft  32  and the inside of the guide sleeve  27 . On the shaft  32 , within the space in the sleeve  25 , is located a valve disk  34 , whose external diameter is somewhat smaller than the external diameter of the piston guide  7 , but larger than the opening  35  located in the associated end of the piston guide  7 . The valve  33  closes this opening  35 . Immediately behind the valve disk  34  are provided two disk springs  36 , whose external diameter is larger than the external diameter of the piston guide  7 . 
     The tubular element  18  is not only sealed with respect to the sleeve  25  in the right-hand part in FIG. 1, but also in the area of the surface  10  with respect to the casing  1  with the aid of a thrust ring  37  and with respect to the piston guide  7 . In the vicinity of its outside the tubular element  18  is constructed in such a way that this external and internal sealing action not only occurs in the position shown, but also when the tubular element  18  is moved away from the web  3  in the direction of the disk  26 . 
     The cavity  9  of the casing contains pressurized gas, which is optionally permeated with a specific quantity of oil. The resulting pressure prevails not only outside the tubular element  18  but, due to the perforations  19  and opening  16 , also in the interior of the piston guide  7 . As the diameter of the push rod  12  is smaller than the internal diameter of the piston guide  7 , said pressure is present on the underside  8  of the piston  11  and urges it into the position shown. A connection  39  is provided in the outer wall of the casing  1  for introducing the pressurized gas. 
     The space within the sleeve  25  between the disk  28  and the end of the piston guide  7  is filled with oil. The release valve  33  is closed by the compression spring  34 s. Thus, the oil in the space within the sleeve  25  cannot reach the piston  11 . The position shown in the drawing in which the piston  11  has moved up to the end of the piston guide  7  and the tubular element  18  is moved into the maximum possible position in the opposite direction, represents the starting position. 
     In the starting position shown the space within the sleeve  25  is filled with oil. For initiating a fitting or insertion process the drive is operated, i.e. for example an electric motor is switched on and with the aid of a transmission rotates the nut  21  with respect to the bolt guide  5 . This rotation leads to a simultaneous longitudinal displacement of the tubular element  18 . In the vicinity of its end facing the release valve  33 , the tubular element  18  has a spacer  40 , which contains lateral recesses  41 . The advance of the tubular element  18  into the oil-filled space within the sleeve  25  leads to a tensioning of the gas spring between the disk  28  and the disk  26 . On reaching a given position the terminal edge of the spacer  40  engages on the disk springs  36 . A further movement now leads to a deformation of the disk springs. On reaching a given position the valve disk  34  is raised from the opening  35  of the piston guide  7 . The entire pressure of the oil now acts on the surface of the valve disk  34  and the end face  14  of the piston  11 . As a result the valve is opened in jerky manner and the piston  11  is driven in the direction of the bolt guide  5 . The pressure is so high that the resulting momentum is adequate for fitting the bolt. During this forward movement of the feed device formed by the piston  11  and the push rod  12 , the pressure in the cavity  9  increases relatively slowly due to the larger size of the space. As a result of this pressure increase the piston  11  is subsequently moved back again. In the intermediate period the tubular element  18  has been further displaced, so that the release valve  33  has also somewhat displaced the disk  28 . This leads to a certain increase in the size in the space within the sleeve  25 , so that the return for moving the piston  11  is facilitated. The tubular element  18  then moves in the reverse direction back into the starting position shown. 
     In the case of the embodiment according to FIG. 2 the piston guide is constructed in two parts in the area facing the release valve  43 . Onto the end of an inner tube  44 , in which the piston  11  is guided together with the push rod  12 , is screwed a sleeve element  45 , which in the axial extension of the piston is provided on its outside with a guide shoulder  45  and on the latter, which corresponds to the guide sleeve in the embodiment of FIG. 1, is guided the disk  28 . 
     The sleeve element has radial openings  46 . The piston  11  has two piston sections  11   a ,  11   b , which are separated from one another by a groove  48  for a seal. In the starting position shown the opening  46  is positioned roughly centrally to the piston section  11   b . Beyond the end face  14  of the piston a radially directed, lateral, small opening  49  leads into the bottom of the sleeve  45 . 
     The release valve  43  has a sleeve-like construction and embraces the radial outside of sleeve element  45 , being urged into the closed position by a spring  34   s . The pressure prevailing in the space within the sleeve  25  admittedly passes through the openings  46  to the piston section  11   b , but cannot attain any feed action there, because it does not reach the end face  14  of the piston. As soon as the displacement of the tubular element  18 , whose end face  50  engages on the opposite end face  51  of the release valve  43 , it has been moved to such an extent that the recesses  52  free the radial, small opening  49 , the pressure now also prevails on the end face  14 . The piston is driven forwards and as soon as the seal located in the groove has reached the opening  46 , the piston movement is further accelerated, because now the entire cross-section of the opening  46  is available. 
     EXAMPLE 
     For driving nails into steel a force of approximately four tonnes is required, for concrete approximately two tonnes and for wood approximately one tonne. 
     The piston speed reaches values of 40 to 50 meters per second. 
     The spring tensioning time is approximately 0.1 second, whereas the relaxing of the spring takes place in roughly one millisecond.