Abstract:
A safety device for a press having a head for applying force, a single fixed pressure source for actuating a low force pressure driven actuator and a high force pressure driven actuator for the head, wherein the operation of the head is limited to only with the low force actuator until the head is in a safe position, when the head is determined to be in a safe position the high force actuator&#39;s use is permitted.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of, under Title 35, United States Code, Section 119(e), U.S. Provisional Patent Application No. 61/078,829, filed Jul. 8, 2008. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to a safety device for presses, and more particularly to those used in ultrasonic welding, staking and inserting machines; vibration welding, staking and inserting machines; and hot plate welding, staking and inserting machines. More specifically, this invention relates to a safety device which limits the amount of force exerted by the press until the head has been determined to be in a safe position. 
     BACKGROUND OF THE INVENTION 
     It is common in various areas of manufacture, such as in the case of punches; and hotplate, ultrasonic or vibration welding, staking, inserting and the like, to provide a head that is caused by a press to move, for example up and down, with respect to a workpiece upon which work is to be performed. It is also common for the press, via the head and typically a tool, to exert a great amount of force upon the workpiece, and for it to be necessary for a human operator to be required to manually adjust the position of the workpiece with respect to the head as the head approaches the workpiece in order to achieve proper working alignment. 
     More specifically, ultrasonic welding is a process whereby ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. During this process the work pieces to be welded together are held under pressure between a fixed anvil and a horn which emits the acoustic vibrations. The pressure generated between the anvil and the horn during the welding process can be quite great. A problem exists, however, in that it is often necessary for an operator to be required to manually position the parts for welding, and if the operator&#39;s hand, or more typically one or more of his/her fingers, is caught between the head or anvil and the work piece, the large force exerted by the press can cause severe and permanent damage to the operator. 
     A number of safety devices, such as guards, sensors and the like, have been developed to reduce the occurrence of operator injury. However, all known safety devices have problems of their own, such as interfering with the operator&#39;s manipulation of the workpiece, requiring expensive add-ons to the press and being subject to tampering and/or removal. 
     One such safety device is disclosed in U.S. Pat. No. 6,418,824, which is a hydraulic press that utilizes a single actuator and is powered by a first low pressure source, to move the press safely to a predetermined position without generating enough force to seriously injure or damage any obstructions. Once the piston has reached its predetermined position, a second high pressure source is supplied to the actuator to complete the cycle. However, this system requires the machine to have two separate pressure sources, which adds a great deal of cost and inefficiency to the process. Furthermore, there are risks of these pressure sources being improperly adjusted or possibly switched, which could result in harm to the operator. 
     What is desired, therefore, is a press which provides the safety advantage of a low force and high force mode but only uses a single fixed pressure source. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a press that utilizes a single pressure source yet provides the advantage of a low force safety mode, for positioning a workpiece with respect to the press, and a high force use mode, which is only activated when it is determined that the head of the unit is a safe distance from the part. A safe distance is that which is small enough where an operator&#39;s finger or hand would not fit between the head and the part. 
     One aspect of the invention involves selecting the proper sized low force and high force actuators to supply the desired force for each mode. For instance, if pressure cylinders are used one can either reference a force chart from the cylinders supplier or it can be calculated. The Force (“F”) exerted by the cylinder can roughly be calculated to equal the Area (“A”) of the piston multiplied by the pressure (“p”) used (F=p*A). Where A equals π multiplied by the diameter (“d”) of the piston squared, divided by 4 (A=π*d 2 /4). 
     Therefore, if one wanted to operate a press at a pressure of 100 psi, with the desired low force of 10 lbs and the desired high force of 100 pounds, the low force cylinder would have an A=0.1 in 2  and approximately a d=0.36 in., while the high force cylinder would have an A=1 in 2  and approximately a d=1.13 in. Thus, one would fit the press with cylinders within these specifications. 
     Still another aspect of the invention could be to have a press set up at a specified high to low force ratio of x:1. For example, if one were to have a machine set up as outline above, the force ratio would be 100:10 or a 10:1 ratio. Setting up a machine at such a ratio can allow an operator to know what range of pressure at which one could safely operate that specific machine. For instance if one was to determine that on the press outlined above the minimum operating pressure at which independently both cylinders could efficiently actuated the head of the machine was 25 psi, this would translate into a minimum low force of 2.5 pounds, and a minimum high force of 25 pounds. Now to calculate the high end of the operating range of the machine one would need to determine at what maximum force the head can be actuated without causing severe injuries. If it was determined that the maximum force the head could exert onto someone without causing severe injuries was 22 pounds this would translate into a maximum operating pressure of 220 psi. This is also assuming that the cylinders operating pressure is also in this range. Therefore, the safe operating range of this particular device with these cylinders would be between 25 and 220 psi. The advantage of having an x:1 ratio is a known safe operating range. Therefore, if a different operating pressure was used, due to the need for more force on the application, fluctuations of the existing supply, or any other reason, one would know whether the device was still in a safe operating range. 
     Still another aspect of the invention involves selecting the proper means for determining when the head is in safe proximity to the part or anvil. This can be achieved, for example, by the use of one or more sensors or switches on the horn or actuator. 
     Other aspects, features and advantages according to the present invention will become apparent from the following detailed description of certain advantageous embodiments when read in conjunction with the accompanying drawings in which the same components are identified by the same reference numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of one embodiment of the present invention, which incorporates low and high force actuators, as well as a sensor for determining when it is safe to allow the high force actuator to function. 
         FIG. 2  is a schematic view of another embodiment of the present invention, which further incorporates a High Force Activation Switch. 
         FIG. 3  is a schematic view of another embodiment of the present invention, which further incorporates an adjustable in-line pressure regulator on both the low force and high force actuators. 
         FIG. 4  is a schematic view of yet another embodiment of the present invention, which further incorporates a lever for mechanical advantage while generating high force. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention as shown in  FIG. 1  is a simplified view of an ultrasonic welding machine  1 , which incorporates a low force cylinder  10 , a high force cylinder  20 , and a control unit  40  used to determine when the head  2  of the press is in a safe position by means of a sensor  41 . 
     The basic press as shown has a frame which includes a base  9 , a rear support  8  and an upper arm  7 . Attached to the upper arm  7  are the low force cylinder  10  and high force cylinder  20 . Each cylinder comprises a housing  11  with an internal cylindrical bore  14 . A piston  12  is encased within the cylinder and is tightly sealed against the cylindrical bore  14 . The piston  12  along with the cylindrical bore  14  create a pressure chamber  15 . Attached to the bottom of the piston  12  is a drive rod  13 , the lower end of which is connected to the head  2 . The drive rod transmits the force generated by the cylinder to the head  2 , attached to which is the horn  3 . During operation the parts to be welded together  4 ,  5  are pressed between the horn  3  and the anvil  6  attached to the base. 
     Pressure from the pressure supply  30  is transmitted to the low force cylinder  10  via pipe  31  and to the high force cylinder  20  via a pipe  32 . The pipe for each cylinder also has an inline valve  44  for the low force cylinder  10  and an inline valve  45  for the high force cylinder  20 . These valves are used to regulate when pressure is supplied to their respective cylinder. 
     The press further comprises a control unit  40 , which regulates when pressure from the pressure supply  30  is transmitted to the low force cylinder  10 , the high force cylinder  20 , or both. The control unit  40  determines the position of the head  2  and/or horn  3 , via a sensor  41 . In this particular embodiment, the sensor  41  is a magnetic proximity sensor located on the low force cylinder  10 . The piston  12  of the low force cylinder  10  has a magnet  42 , fixed into a center bore of the piston  12 . It should be noted that this is just one embodiment of the present invention and the sensor can be any type of sensor, including a switch, and the placement of the sensor can be anywhere on the press where it can determine the position of the head  2  and/or horn  3 . 
     The press also has a start switch  43  which can be directly connected to the valve  44  for the low force cylinder  10 , to the control unit  40 , or both. If the start switch  43  is only connected to the control unit  40  then it would be necessary for the control unit  40  to be connected to both the low force cylinder valve  44  and the high force cylinder valve  45 . These are only a few ways in which the unit can be configured and in no way is to limit the amount of configurations. 
     The present configuration in  FIG. 1  has the start switch  43  directly connected to the low force cylinder valve  44  and the control unit  40 . It should be noted that the connection to the control unit  40  is not necessary in this configuration but could be advantageous to tell the control unit  40  that the press is in operation. 
     The operation of the ultrasonic press as disclosed in  FIG. 1  is as follows. The operator of the press positions the first part  4  and second part  5  on top of one another on the anvil  6  in the desired positions. Once the parts are in position the operator activates the start switch  43 , which would open the low force cylinder valve  44  actuating the low force cylinder  10 , which safely lowers the head  2  and horn  3  assembly down onto the parts. Once the horn  3  is determined to be a safe distance to the parts, the magnetic proximity  41  sensor will detect the magnet  42  in the low force cylinder&#39;s piston  12 . The sensor then sends a signal to the control unit  40  which open&#39;s the high force cylinder valve  45 . Once the high force cylinder  20  is engaged the press would have the proper high force needed to complete the ultra sonic welding process. It should be noted that the low force cylinder  10  can continued to be pressurized during the welding process or once the high force cylinder  20  is pressurized the low force cylinder  10  can be unpressurized. 
     In this specific configuration the cylinders are transmitting their force directly to the head  2  through the drive rods  13  and therefore, the force created by each cylinder is transmitted directly to the parts  4 ,  5 . One advantage of this configuration is being able to set up the press at a fixed high force (“HF”) to low force (“LF”) ratio (“HF:LF”) of x:1. The Force (“F”) exerted by a pressure cylinder can roughly be calculated to equal the Area (“A”) of the cylinder&#39;s piston multiplied by the pressure (“p”) used (F=p*A). Where A equals π multiplied by the respective cylinders piston diameter (“d”) squared, divided by 4 (A=π*d 2 /4). If the low force cylinder&#39;s  10  piston  12  diameter is DL and the high force cylinder&#39;s  20  piston diameter is DH then the HF:LF would be p*π*DH 2 /4: p*π*DL 2 /4. Simplifying the equation makes the HF:LF ratio equal to DH 2 :DL 2  or DH 2 /DL 2 :1. The advantage of this is that the operator of the press will be able to easily determine how much force each cylinder is making at a given pressure. For instance if the HF:HL ratio is 10:1 and the operator needed a high force of two hundred pounds for a particular welding application he would in turn also know that the low force cylinder  10  is generating twenty pounds of force. Therefore, the operator would easily be able to change the machine for different welding applications and know if the low force cylinder  10  was in a safe operating range to prevent injuries. It should be noted that for this specific formula to be accurate the low force cylinder  10  is depressurized when the high force cylinder  20  is pressurized. 
       FIG. 2  is similar to the embodiment of  FIG. 1  except it incorporates a high force activation switch  50 . The high force activation switch  50  adds several advantages in safety and usefulness to the present invention. One such advantage is that the full operation of the unit could require the user to hold down the start switch  43  and the high force activation switch  50  with separate hands. This would allow a user to lower the horn  3  onto the parts by depressing the start switch  43  with one hand and still have the second hand free to ensure the parts to be welded stay in the proper position. Once the head is holding the parts into place using the low force cylinder  10  the operator can then take his free hand and depress the high force activation switch  50  starting the welding process. By requiring the user to hold down both the start switch  43  and the high force activation switch  50  with separate hands this ensures that the high force cylinder  20  cannot be activated while the users hand is near the head  3  of the press. 
     Another advantage of the high force activation switch  50  is that it prevents the accidental start of the welding process if the parts are not in the proper alignment. This would happen if the machine was set up to automatically pressurize the high force cylinder  20  as soon as the control unit  40  received a signal from the sensor  41  that the head  2  or horn  3  of the unit was in a safe position. If the parts were not properly aligned under the head  3  but are in such a way that the head  3  is determined to be in a safe position, an injury could occur if, say, the parts were shot out of the press under the force because the head was not pressing flush. By having the high force activation switch  50  present, a user would be able to visually inspect the parts&#39; placement under the head  3  before the high force cylinder  20  is pressurized. 
     The ultrasonic press can also be setup where the start switch  43  and high force activation switch  50  only control the cylinders and a third switch(not shown), which could possibly be in the form of a foot pedal, could be used to start the ultrasonic welding process once the high force cylinder  20  is engaged. These are just but a few ways in which the switches can be set up and in no way is to limit the way in which the press can be set up to operate. 
       FIG. 3  is similar to the embodiment of  FIG. 1  except it incorporates an in-line adjustable pressure regulator  46  on the low force cylinder  10  and an in-line adjustable pressure regulator  47  on the high force cylinder  20 . This configuration adds several advantages in safety and usefulness to the present invention. One such advantage is that for the welding of some parts an operator may want to have the high force cylinder  20  generate less force so as to not damage the parts ( 1 ,  2 ) but at the same time have the low force cylinder  10  still operating at its maximum force to properly hold the parts ( 1 , 2 ) in place. Still yet another advantage of being able to adjust the force that each cylinder generates is that the operator would also be able to lower the force generated by the low force cylinder  10  so he would be able to more easily position the parts ( 1 ,  2 ) before the high force cylinder  20  was activated. 
     It is important to note that it is not necessary to have an in-line adjustable pressure regulator on both the high force cylinder  20  and the low force cylinder  10 . For instance if the low force cylinder  10  is properly sized it will not generate enough force to harm the operator even when connected directly to the pressure supply  30 . Therefore, one might only have an in-line adjustable pressure regulator  47  on the high force cylinder  20 , since the low pressure cylinder  10  is not able to generate enough force to harm the operator even at the maximum pressure supplied by the pressure source  30 . Furthermore, sizing the low force cylinder  10  so that it is unable to generate enough force at the maximum line pressure can be an important safety factor in preventing any accidental injuries caused by any accidental adjustments of the pressure supplied to the low force cylinder  10 . 
       FIG. 4  is similar to the previous two embodiments of the present invention; however, the high force cylinder  20  is moved to a position where it can also use mechanical advantage in applying force. In this embodiment the high force cylinder  20  is positioned behind the rear support  8  on the base  9 . A lever  60  is connected at one end to the drive rod  13  of the high force cylinder  20  by a pin  61  and at the other end to the drive rod  13  of the low force cylinder  10  by a pin  62 . The lever  60  is connected to the rear support  8  via a bearing  62 . The bearing  62  should be in closer proximity to the drive rod  13  of the low force cylinder  10  in order to achieve the desired mechanical advantage. 
     One advantage of this particular embodiment is that both the low force and high force modes are transmitted through one centrally located drive rod  13  on the low force cylinder  10 . The advantage of this is that the press is able to exert a centrally located uniform force across the whole horn  3 , which in turn provides an even welding of the parts. 
     Another advantage of this embodiment is that a lower operating pressure can be used, yet the press will still be able to generate the high force necessary for the welding process. However, since the high force cylinder&#39;s  20  force will be multiplied through the use of the lever  60  and because the lever&#39;s  60  force amplification changes with its angle the HF:LF ratio as described above will no longer be applicable. 
     Variations from the described embodiments can be implemented by one skilled in the art without departing from the scope of the invention as set forth by the following claims.