Patent Publication Number: US-6342750-B1

Title: Vibration drive for a mold

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a vibration drive for a machine for producing shaped concrete bodies from a mold which is placed on a vibrating table and filled with flowable concrete, more particularly, to such a vibration drive utilizing one or more piezoelectric vibration exciters connecting a vibrating table to the frame of the machine. 
     In such vibration drives, cam and eccentric motors have generally been used in order to cause the vibrating table of the molding machine to vibrate. As a result, the mold which is open at the top and bottom and which is positioned on the vibrating table is similarly caused to vibrate and shaken in order to compact the concrete mass which has been placed in the mold cavities as uniformly as possible. During the shaking process, the opened top of the mold is generally closed using vertically movable pressure plates which move downwardly from overhead into the mold cavities and press on the concrete mass. 
     The disadvantage in such known structures is that the mechanical eccentric motors provide largely uncontrolled shakey movements which can lead to damage and premature wear phenomena of the mold. Therefore, the mold and the vibrating table must be built to be very strong and is thus more complex. In addition, the mold machine and the mold are often not optimally matched to one another with respect to vibration engineering. The same also applies to the concrete mass which has been placed in the mold and which, depending on the type, volume, grain size, moisture content, specific weight and other properties requires different vibration parameters such as vibration frequency, vibration duration, vibration path, vibration direction and others. These discrepancies of matching leads to nonuniform filling of the mold cavities and to nonuniform compaction of the concrete mass within the mold. As a consequence thereof, the finished moldings are of relatively poor quality. Also, the molds which must be made thicker and the relatively heavy vibrating table also require much higher vibration energy. 
     The German published patent application DE OS 38 37 686 discloses a three-dimensional vibration system in which a mold which is filled with a concrete mass is kept in resonant vibration to produce the concrete mold bodies. The mold is supported by bearing springs on the machine frame and is caused to vibrate by means of vibration exciters in the form of eccentric motors. Sensors indicate various parameters such as the stiffness and damping of the bearing springs and the resonant frequency of the vibration system is measured and monitored in a microprocessor. When the resonant frequency is exceeded or not attained, a corresponding correction occurs by changing the bearing spring parameters in order to keep the vibration system at the desired resonant frequency. In this manner, optimum vibration conditions will be created with low input power. 
     This known prior art structure which has not yet been put into practice has the disadvantage that conventional mechanical eccentric motors are always used as the vibration exciters, but they are not especially well-suited to the control of the exciter frequency. The additional construction which is required to control the exciter frequency by changing the bearing spring parameters is very considerable. At the beginning and end of the shaking process the mechanical eccentric motor traverses a rpm. range from zero to maximum and back again. In so doing, the individual components or groups of components are briefly excited to the natural frequency. This results in damage and additional noise. Further, the cycle time of the molding machine is considerably lengthened. 
     SUMMARY OF THE INVENTION 
     It is the principal object of the present invention to provide a novel and improved vibration drive for a machine for producing shaped concrete bodies from a mold. 
     It is another object of the present invention to provide such a vibration drive which can be readily adjusted according to the various requirements of practice in order to ensure optimum vibration behavior of the mold and thus high quality of the final product. 
     The objects of the present invention are achieved and the disadvantages of the prior art as described above are overcome by the vibration drive of the present invention which has at least one piezoelectric vibration exciter with a stationary portion which is connected to the machine frame and a vibrating member which is connected to the vibrating table. 
     In order to directly transmit vibrations, a vibrating member of the vibration exciter is connected to a piezoelement through a transducer which may comprise a hydraulic fluid. The piezoelement is clamped in the stationary portion of the vibration exciter so as to be able to vibrate freely. A first or larger piston is connected to the piezoelement and vibrations are transmitted through a hydraulic fluid to a second or smaller piston which is attached to the vibrating member of the vibration exciter. Downward or return movement of the second piston can be enhanced by a return spring. The piezoelement may be a ceramic. 
     In order to achieve a simple, vertical shaking motion of the mold in one embodiment there is provided one vibration exciter in each of the four corner areas of the rectangular vibrating table and each exciter has a vertical vibration direction. 
     Another modification of the present invention provides for three-dimensional vibration of the mold and different directions of vibration. This is achieved by mounting a vibration exciter in each of the four corner areas of the vibrating table but with the longitudinal or vibration axis of each exciter being at an angle with the vertical which angle is preferably 45 degrees. It is preferable that the vibration exciters are connected by spherical bearings to the vibrating table and/or the machine frame. These spherical bearings preferably consist of ball- and socket joints. 
     A further modification of the present vibration drive can be applied to a molding machine having pressure plates which correspond to the mold cavities and which can be moved vertically by lifting elements from overhead to press on the concrete mane in the mold cavities. To reinforce the vibratory motion one or more vibration exciters may be interconnected between the pressure plate lifting elements and the pressure plates. As a result, an additional vibratory or shaking motion is applied through the pressure plates to the concrete mass and the distribution and compaction of the concrete mass and the mold cavities are significantly improved. 
     In order to obtain optimum vibratory action under different operating conditions, parameters of the vibration drive such as the vibration frequency, vibration duration, vibration path, vibration direction and the number of activated vibration exciters can be varied. This can be accomplished by connecting the vibration exciters to a microprocessor which contains one or more preselectable programs for adjusting the required parameter quantities of the vibration drive. The vibration exciters can be activated or controlled individually or in predetermined groups. 
     The advantages and results achieved with the present vibration drive is that the utilization of the piezoelectric vibration exciters enables one to vary the vibration drive with different operating conditions, depending on the product, and characteristics of the concrete mass to result in a high quality bolded concrete body. The use of the piezoelectric vibration drive as disclosed herein instead of the conventional eccentric motors makes it possible to generate the desired exciter frequency immediately and relatively easily. The energy required to produce vibrations is significantly reduced and the noise of the process is greatly decreased. Further, the vibration metal bearings which are located between the vibrating table and the vibrating frame in a conventional vibratory machine and which absorb a large part of the exciter frequency are eliminated in the present invention. Further, since the vibration exciters of the present invention also support the vibrating table, an empty space is formed underneath the mold which can be used for inserting mold cores or recess bodies into the mold. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     Other objects and advantages of the present invention will be apparent upon reference to the accompanying description when taken in conjunction with the following drawings, which are exemplary, wherein; 
     FIG. 1 is an overall perspective view of a molding machine with a vibration drive for a vertically vibrating mold; 
     FIG. 2 is a front elevational view of the molding machine shown in FIG. 1; 
     FIG. 3 is a longitudinal cross sectional view through a vibration exciter in an enlarged scale; 
     FIG. 4 is an overall perspective view of a molding machine with a vibration drive for a mold which vibrates in three-dimensions; 
     FIG. 5 is a schematic block diagram of the electronic vibration exciter control; 
     FIG. 6 is a front elevational view of the molding machine including another embodiment of the present invention; and 
     FIG. 7 is a sectional view taken along the line VII—VII in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views a specific embodiment and modifications of the present invention will be described in detail. 
     As may be seen in FIG. 1, there is a molding machine indicated generally at  1  for producing concrete mold bodies and having a machine frame  2  with four vertical guide columns  3  which at their top ends are connected to each other by a plate  4 . The mold supporting plate  5  carrying a mold  6  which has mold cavity  7  which are open at their tops and bottoms is supported to move vertically on the guide columns  3 . The mold  6  can be moved up and down in the conventional manner by hydraulic cylinders, which are not shown and can be positioned on a vibrating table  8  or a mold board  8 ′ which is positioned on the vibrating table. On the bottom of the rectangular vibrating table  8  there is connected a vibrating member  9  of a piezoelectric ceramic vibration exciter  10  positioned in each of the four corner areas of the vibrating table. The exciter  10  also has a stationary portion  11  which is connected to the machine frame  2 . After the mold cavity  7  is filled with a suitable concrete mixture, the vibration exciters  10  are activated by the application of an AC voltage and are caused to vibrate back and forth which motion is transferred to the vibrating table  8  and the mold  6  which is positioned upon it. The vibration exciter  10  has a longitudinal axis  12  which is at the same time the direction of vibration of the vibrating member  9  and this longitudinal axis is aligned vertically so that the vibrating table  8  will oscillate up and down relative to the machine frame  2 . The result is a uniform compaction of the concrete mass in each of the mold cavity  7 . 
     Above the mold  6 , a force plate  13  is mounted to move vertically on the guide columns  3  and is driven in the conventional manner by lifting elements which may be hydraulic cylinders (not shown in the drawings). On the bottom of the rectangular force plate  13  in each of its four corners, a stationary portion  11  of the vibration exciter  10  is attached and the vibrating member  9  is connected to a holding plate  14 . On the bottom of the holding plate  14  there are supported several pressure plates  15  which are correspondingly positioned to each of the individual mold cavities  7  of the mold  6 . When the force plate  13  is lowered, the pressure plates  15  are positioned into the mold cavity  7  and press on the concrete masses in each of the cavities. When a voltage is applied to the vibration exciters  10 , the pressure plates  15  will vibrate vertically and these vertical vibrations will be transferred to the concrete masses in each of the mold cavities. In this manner, in addition to the shaking motions of the vibration table  8  an additional vibrating action is exerted by the pressure plates  15  on the concrete masses so that a significantly better distribution and compaction of the concrete mass is achieved in each of the mold cavities. 
     As may be seen in FIG. 3, each vibration exciter  10  has a conventional piezoelement  16  in the form of a ceramic plate which is clamped to vibrate freely in the stationary portion  11  of the exciter. This stationary portion  11  is constructed as a housing for the exciter. An electrical AC voltage can be applied to the ceramic plate  16  as shown in FIG. 3. A piston  17  is securely connected, but is interchangeable, to the piezoelement  16  and the piston  17  is guided to move vertically in a cylindrical space  18  within the stationary housing  11 . The space  18  is filled with a hydraulic fluid. At the upper portion of the cylindrical space  18 , there is a second cylindrical space  18 ′ which has a smaller diameter. In the cylindrical space  18 ′ there is similarly located in the stationary portion or housing  11  a second piston  19  which is also guided to move vertically. The second piston  19  is smaller in diameter than the first piston  17  and is securely connected to the vibrating member  9  of the vibration exciter  10 . 
     Thus, when an AC voltage is applied to the piezoelement  16 , pulses of vertical motion are then transmitted by the piston  17  to the hydraulic fluid and to the second piston  19  and thus to the vibrating member  9 . These pulses are produced by the expansion of the piezoelement  16 . In this manner, a vibrating member  9  and also the vibrating table  8  to which the vibrating member  9  is attached are caused to vibrate vertically. A downward movement of the piston  17  creates a suction force between the piston  17  and the piston  19  and this suction force is supported and assisted by a return spring  20  which acts on the piston  19  in a downward direction. 
     The pistons  17  and  19  interconnected by a hydraulic transducer enables the magnitude of the vibration or distance of the vibration path of the mold to be increased or decreased with respect to the vibration amplitude of the piezoelement  16 , which may be for example, quartz. Since in this embodiment the second piston  19  has a smaller diameter than the piston  17  the magnitude of vibration of the mold is thus increased. 
     In the event the vibration exciter  10  is operated without hydraulic fluid in the cylindrical spaces  18 ,  18 ′ there no longer is a transducer component and there is now a solid connection between the two pistons,  17  and  19 . The vibratory movements of the piezoelement  16  are transmitted in both directions directly to the vibrating member  9 , the return spring  20  can thus be eliminated. 
     FIG. 4 shows a modification of the invention in which the vibration exciters  10  are mounted at angles to the horizontal and to the vertical and not vertically as previously described. This is achieved by providing four brackets  21  mounted on the corner areas of the machine frame  2  and each bracket  21  has an inclined upper end  22  to which the stationary portion  11  of the vibration exciter  10  is attached. The vibrating member  9  of the vibration exciter is connected to corresponding receiving plates  23  on the vibrating table  8 . The top ends  22  of the brackets  21  are angled to such an extent that when the vibration exciter  10  is attached, its longitudinal axis  12  which is at the same time the direction of vibration of the vibrating member  9  is inclined at an angle of 45 degrees to both the vertical and horizontal. When a voltage is supplied to the vibration exciters  10 , the result is a three-dimensional vibration of the vibrating table  8  with a correspondingly intensified vibratory action on the mold  6 . This three-dimensional vibration requires that the stationary portions  11  of the vibration exciters  10  are spherically supported on the brackets  21  and the vibrating members  9  are spherically supported on the receiving plates  23  of the vibrating table  8  in ball-and-socket joints  24 . 
     In the modification as shown in FIG. 4, the arrangement of the vibration exciters  10  between the force plate  13  and the pressure plates  15  is eliminated. As a result, the pressure plates  15  are securely connected to the force plate  13 . 
     FIG. 5 shows schematically an electronic control of the vibration exciters  10 . Frequency controllers  25  which can be activated in a known manner through a microprocessor  26  can be used to change the vibration frequency of the individual vibration exciters  10  which may depend on the type of concrete mix which has been placed in the mold cavity  7 . Various other parameters of the vibration drive including the vibration duration, the vibration path, the vibration direction, and the number of vibration exciters which are activated can be automatically controlled by correspondingly preselectable computer programs which are used in a known manner with the microprocessor  26 . By way of example, an asymmetrical concrete mold body having an angular cross section is to be molded, one side of the mold cavity will have a greater amount of the concrete mix than on the other side. In order to maintain uniform compaction of the concrete mass, a greater vibration energy must be applied to the side of the mold having the larger portion of concrete. This can be achieved by activating only one or both vibration exciters  10  which are on the side of the larger concrete mass in the embodiment as shown in FIG.  4  and by not operating the other vibration exciters or doing so with a smaller vibration frequency. In this manner, the direction and path of vibrations can be changed as may be desired based upon varying conditions encountered with the concrete mass. 
     As a further modification, sensors may be attached to the mold to monitor vibration behavior and the resulting vibration data are recorded and then relayed to the microprocessor to control the vibration exciters. This modification provides a real time capable, adaptive control system which can be adjusted to the respective operating conditions by computer control or in a self-regulating manner. The piezoelectronics can thus be used both as sensors and also as actuators. 
     In another modification the vibration exciters  10  exert a vibratory action on the mold  6  and the mold board  8 ′ as shown in FIGS. 6 and 7. In this modification, the vibrating table  8  comprises three parallel longitudinal beams  27  which are spaced from each other and which form a vibration frame  28 . The vibration frame  28  is securely connected to the vibrating members  9  of the vibration exciters  10  and has three vibrating strips  29  which are attached to the longitudinal beams  27 . The vibrating strips  29  are positioned transversely to the longitudinal beams  27  and are spaced from each other. The tops of the vibrating strips  29  form a common vibration plane  30  which is spaced slightly below a support plane  31  for the molding board  8 ′. 
     The mold board  8 ′ is supported by six support strips  32  which are spaced from each other and which are parallel to the vibrating strips  29 . The support strips  32  are connected by supporting rods  33  to four carrier members  34  of a support frame  35  and which run parallel to the longitudinal beams  27  of the vibration frame  28 . The support frame  35  is spaced below the vibration frame  28  and is attached to the machine frame  2 . In this structure, there is one vibrating strip  29  between each pair of support strips  32  mounted on support rods  33  which extend downwardly through the vibration frame  28 . The longitudinal beams  27  of the vibration frame  28  are located between the carrier members  34  and the support strips  32  which run transversely to the carrier members. The tops of the support strips  32  thus form the support plane  31  for the mold board  8 ′. 
     When the vibration drive is actuated, the vibrating strips  29  are moved up and down by the vibration exciters  10  according to the vibration frequency. The vertical distance between the vibration plane  30  and the support plane  31  is such that the vibrating strips  29  in their uppermost positions contact the bottom of the mold board  8 ′ and thus produce the desired vibratory action on the mold  6 . In a known manner, the distance between the vibration plane  30  and the support plane  31  can be varied by vertical adjustment of the vibrating strips  29  or in some other known manner. This means that at a larger vibration amplitude the distance between the planes  30  and  31  must also be greater. 
     The vibration structure as illustrated in FIGS. 6 and 7 has the advantage that the vibratory action of the vibrating strips  29  will result in better compaction of the concrete mix and reduces the vibration time under particular conditions which may include a low proportion of moisture in the concrete mix. Concrete residue which may escape from the mold or may be formed by spills can drop down unhindered through the lattice construction of the vibration frame  28  and the support frame  31 . As a result, fouling of the molding machine is significantly reduced. 
     Thus it can be seen that the present invention provides a vibration drive for a concrete molding machine which can be readily adjusted for a variety of conditions such as composition of the concrete mix. 
     It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.