Abstract:
An integrated vacuum and magnetic gripper includes a rigid housing defining an internal chamber, and a flexible vacuum cup operatively connected thereto. A vacuum cavity is defined by the vacuum cup and a vacuum source is configured to reduce pressure in the vacuum cavity. A permanent magnet is disposed within the rigid housing, and a magnet release mechanism is configured to selectively render the magnet incapable of exerting sufficient force to hold the work piece. A pole plate may be interposed between the internal chamber and vacuum cavity, such that the pole plate forms a portion of the internal chamber and may act to provide friction on the work piece. A method of using the gripped includes operating at high acceleration while the vacuum gripper is monitored as fully operational and operating only at lower acceleration while the vacuum gripper is not fully operational.

Description:
TECHNICAL FIELD 
     This invention relates to devices and methods for lifting and transporting objects in industrial applications, such as for movement through assembly processes. 
     BACKGROUND OF THE INVENTION 
     Industrial manufacturing processes often include repetitive lifting and transportation of work pieces that are too heavy, too large, too fragile, or must be placed with too high precision to be lifted without mechanical assistance. The lifting and transportation of these work pieces may be accomplished manually or through automated means with material handling devices. Gripping devices allow heavy, large, and complex work pieces to be transported through manufacturing processes with increased reliability and efficiency. 
     Vacuum-based grippers require backup mechanical clamps capable of maintaining control of the work piece or work pieces in the event of partial or total loss of vacuum pressure. Furthermore, vacuum grippers are capable of generating gripping force in only a single direction (created by air pressure on the opposite side of the vacuum chamber) and may require redundant gripping mechanisms and/or friction to hold the work piece while rotating or moving along more than one axis. 
     Permanent magnet-based grippers may not require backup mechanical clamps capable of holding the work piece in the event of power loss. However, these grippers often require additional structure to mechanically release the work piece from the gripper and work only on ferrous materials. Additionally, permanent magnet grippers are often incapable of picking up only one work piece from a stack or inventory of work pieces and have difficulty picking up parts of varying shapes. 
     SUMMARY OF THE INVENTION 
     A unique integrated lifting and transport device providing increased flexibility and lower investment costs is provided. The lifting and transport device includes a rigid housing defining an internal chamber. A flexible vacuum cup having an interface end is operatively connected to the rigid housing. The flexible vacuum cup also has a sealing and gripping end opposite the interface end, and a vacuum cavity defined between the gripping end and interface end. 
     A vacuum source is configured to reduce pressure in the vacuum cavity. A permanent magnet is disposed within the internal chamber of the rigid housing, and a magnet release mechanism is configured to selectively render the permanent magnet incapable of exerting sufficient force to hold the work piece. A pole plate may be interposed between the internal chamber and vacuum cavity, such that the pole plate forms a portion of the internal chamber. 
     The pole plate may act as a pressure foot providing friction force for the vacuum gripper. This device includes unique integrated structures for releasing the magnetic gripper, allowing for backup gripping while maintaining an ability to release the work piece, and minimizing damage to the work piece or surrounding equipment. Furthermore, these integrated structures control and direct the magnetic field generated by the magnetic gripper, which provides enhanced flexibility, reliability, and efficiency in the manufacturing processes. 
     A method of using an integrated magnetic and vacuum gripper to lift and move a work piece through a multi-stage manufacturing process is also provided. The method includes lifting and holding the work piece with a lifting and transport device having a vacuum gripper capable of holding the work piece while subjecting the work piece to a high maximum acceleration and speed. The lifting and transport device also has a magnetic gripper capable of holding the work piece while the lifting and transport device subjects the work piece to lower maximum accelerations and speeds. 
     The method further includes monitoring the vacuum gripper to determine if it has sufficient vacuum pressure to hold the work piece while the lifting and transport device subjects the work piece to the high maximum acceleration. The lifting and transport device operates at the high maximum acceleration as long as the vacuum gripper has sufficient vacuum pressure to hold the work piece. The lifting and transport device lifts and holds the work piece with the magnetic gripper and operates at the lower maximum acceleration when the vacuum gripper does not have sufficient vacuum pressure to hold the work piece. The lifting and transport device may continue to operate at the lower maximum acceleration until the multi-stage manufacturing process reaches a predetermined maintenance point or break. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes and embodiments for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross section of one embodiment of an integrated vacuum-magnetic gripper; and 
         FIG. 2  is a flow chart diagram of one embodiment of a method of using an integrated vacuum-magnetic gripper to lift and move a work piece through a multi-stage manufacturing process. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, there is shown in  FIG. 1  a cross sectional view of a portion of one embodiment of an integrated releasable vacuum-magnetic gripper  10  (hereinafter referred to as integrated gripper  10 ). 
     A rigid housing  12  acts as a structural support for the integrated gripper  10 , which has two gripper units: a vacuum gripper  13  and a magnetic gripper  25 . As will be recognized by those having ordinary skill in the art, rigid housing  12  may be constructed of panels or sheets on a frame, or may be a unitary or integral structure. 
     Attached to the rigid housing  12  is a vacuum cup  14  which acts as the primary gripping device and flexible seal for the vacuum gripper  13  of integrated gripper  10 . The vacuum cup  14  forms a vacuum cavity  16  which can be evacuated of air by a vacuum source  22 . This creates a relative vacuum in vacuum cavity  16 , which lifts a work piece  30  (by the relative force created by atmospheric air pressure opposite the work piece  30  from the vacuum), which is in contact with a gripping lip or gripping end  18 . 
     Vacuum cup  14  may be constructed of a molded elastomer. The gripping end  18  may be molded integrally as a flexible annular lip capable of providing a pressure seal on the surface of the work piece  30 . Those having ordinary skill in the art will recognize other materials and various shapes capable of holding a vacuum and sealing along gripping end  18  that may be used for construction of the vacuum cup  14 , and will further recognize that gripping end  18  could be made of a different, or differently-treated, material than the remainder of vacuum cup  14 . 
     The vacuum source  22  could be attached directly to the vacuum cup  14 , or create the vacuum through a central channel  24  in the rigid housing  12  (as shown in the embodiment of  FIG. 1 ). As will be recognized by those having ordinary skill in the art, some embodiments of the vacuum cup  14  may incorporate multiple vacuum chambers  16 , each in communication with the vacuum source  22 , to maintain multiple sources of vacuum pressure. 
     A vacuum sensor  23  may be included in the rigid housing  12 , located directly in the central channel  24  (as shown in  FIG. 1 ), or elsewhere in the vacuum generation system (which includes vacuum source  22 ). One advantage to having the vacuum sensor  23  in the rigid housing  12  or central channel  24  is that it could detect vacuum cup  14  sealing issues, cup rips or damage; or upstream leaks, hose kinks and other issues with the transmission of vacuum pressure from the vacuum source  22  to the rigid housing  12  and vacuum chamber  16 . 
     The vacuum cup  14  attaches to the rigid housing  12  via a hub or interface end  20 . To facilitate maintenance, repair, and flexible operation of the integrated gripper  10 , the interface end  20  is configured to be attached, removed, and reattached to the rigid housing without damaging the vacuum cup  14 . As will be recognized by those having ordinary skill in the art, the same or similar interface end  20  could be incorporated into differently-shaped vacuum cups  14 , allowing multi-functionality in the vacuum cup design while retaining the same rigid housing  12 . 
     Within the rigid housing  12  is a magnetic field source  26 , which may be a single magnet or an array of magnets, and acts as the primary gripping device for the magnetic gripper  25 . In the embodiment shown in  FIG. 1 , magnetic field source  26  is an array of two permanent magnets supported by a plate  27 . However, as will be recognized by those having ordinary skill in the art, magnetic field source  26  could be a larger array of permanent magnets, or an array of both permanent and electromagnets. 
     The magnetic field source  26  and plate  27  separate the interior of the rigid housing  12  into two chambers, a magnetic chamber  34  and a spring chamber  36 . A vent mechanism  44  may be used to regulate pressure in the spring chamber  36 . 
     In operation, the integrated gripper  10  may be attached to a robot (not shown) or another multi-dimensional actuator (not shown), by mounting the rigid housing  12 . The robot or other end effector would be capable of moving the integrated gripper  10  and the work piece  30  through a manufacturing process or processes. In such an application, the magnetic gripper  25  may function as either (or both) a primary or a backup gripper. Furthermore, multiple integrated grippers  10  may be attached to a robot or array of end effectors to handle multiple work pieces  30  or operate together to handle a large, complex-shaped work piece  30 . 
     While the integrated gripper  10  is functioning normally, the vacuum gripper  13  carries the whole load of work piece  30  while the integrated gripper  10  moves at full speed through the manufacturing process. However, if there is a loss of vacuum pressure—caused by damage to the vacuum cup  14  or a power failure in the vacuum source  22 , et cetera—the magnetic field source  26  can engage the work piece  30 , such that the work piece  30  is carried by the magnetic gripper  25 . 
     Both the vacuum and magnetic gripper  13  and  25  can be operated independently or in tandem to control the work piece. In the case of tandem operation, the magnetic gripping function ( 25 ) acts as a back-up part retention reserve system in case the vacuum is lost at any time during the lifting and transport sequence. In the case of a pause, activity break, or other extended shut down of the lifting and transport sequence, the magnetic retention system ( 25 ) would statically maintain control of the work piece  30  without the sustained energy requirements to generate a continuous vacuum pressure, thus providing a relative energy savings. 
     Engagement of the magnetic field source  26  can be triggered in myriad ways. One mechanism to engage the magnetic field source  26  is a spring  28 , which biases the magnetic field source  26  towards the work piece  30 . In such an embodiment, the magnetic gripper  25  is both a primary and backup gripper and operates in tandem with the vacuum gripper  13 ; it provides gripping force whenever the work piece  30  is engaged with the vacuum cup  14 , but also continues to grip work piece  30  if vacuum pressure is lost. 
     To release the work piece  30 , both the vacuum and magnetic gripping mechanisms  13  and  25  need to be released. Selective release of the vacuum gripper  13  occurs simply by turning off the vacuum source  22  or otherwise removing or venting the vacuum inside of vacuum cavity  16 . Alternatively, the external vacuum generation system (including vacuum source  22 ) can provide this function, including the temporary application of positive pressure to the vacuum cavity  16  to assist in quickly reliving the vacuum and providing a part “blow-off” function. 
     To selectively release the magnetic gripper  25 , myriad options are available. One method of releasing the magnetic gripper  25  involves physically moving the magnetic field source  26  away from the work piece  30  (rightward, as viewed in  FIG. 1 ). This movement can be accomplished by a physical actuator (not shown) or by introducing compressed air from a pressure source  32  into the magnetic chamber  34 . Increased pressure in the magnetic chamber  34  biases the magnetic field source  26  away from the work piece  30 . 
     Gas exchange, and therefore pressure regulation, between pressure source  32  and magnetic chamber  34  is maintained by regulator mechanism  33 . As will be recognized by those having ordinary skill in the art, some embodiments of regulator mechanism  33  could also control pressure in the spring chamber  36 . Alternative methods of rendering the magnetic field source  26  incapable of exerting sufficient force to hold the work piece  30 , and thereby releasing the work piece  30 , are discussed below. 
     Combination of both the vacuum gripper  13  and magnetic gripper  25  in the integrated gripper  25  may allow the integrated gripper  10  to operate without backup mechanical clamps. Furthermore, magnetic gripper  25  is capable of holding the work piece  30  indefinitely during power outages or other loss of vacuum function. 
     Attached to, or forming a portion of, the rigid housing  12  is a pole plate  38 . This integrated pole plate  38  sits between the magnetic chamber  34  and the vacuum cavity  16  and serves several functions in the integrated gripper  10 . Pole plate  38  focuses and conducts the magnetic field produced by magnetic field source  26 , which results in a magnetic gripping force that is more precise and less likely to damage the work piece  30 . 
     In the embodiment shown in  FIG. 1 , pole plate  38  is generally disc shaped and vacuum cup  14  generally conical. However, those having ordinary skill in the art will recognize that the shape of the vacuum cup  14  and either the pole plate  38  or associated area of rigid housing  12  may be modified for specific applications to accommodate different shapes and sizes of the work piece  30 . 
     Vacuum grippers can provide force along only one axis (running left to right in  FIG. 1 ). Therefore, in order to restrict lateral movement and rotation, the vacuum gripper  13  must use friction to restrain the work piece  30  while the integrated gripper is using primarily vacuum pressure to hold work piece  30 . 
     The friction force is provided by a pressure foot in the integrated gripper  10 . In this embodiment, pole plate  38  acts as the pressure foot for the vacuum cup  14 . Other embodiments may incorporate a friction surface  39 —such as thin webbing or other friction-inducing surfaces and structures—molded into the center of the vacuum cup  14  in close contact with the underlying pole plate. 
     The friction surface  39  of pressure foot (such as pole plate  38 ) may also have a layer of thin, high friction material such as an elastomer. This area may also be slightly relived with shallow grooves in a cross or other pattern that allows the vacuum access to the interface between the pressure foot and the work piece  30 . This area could also be optimized to minimize the gap between the pole plate  38  and the part for the most effective magnetic circuit. 
     The embodiment of an integrated gripper  10  shown in  FIG. 1  further includes an electromagnet  40  within the rigid housing  12 . The electromagnet  40  can be selectively energized to assist the magnetic field source  26  in gripping the work piece  30 . In one embodiment, the electromagnet  40  can also be selectively energized to neutralize or reverse the magnetic field produced by the magnetic field source  26 . Such an embodiment would allow the magnetic gripper  25  to release the work piece  30  without the need to physically move the magnetic field source  26  away from the work piece  30 . 
     Some applications may require the integrated gripper  10  to pick up and move a thin, ferrous work piece  30 , such as sheet metal, from a stack without removing more than one work piece from the stack. One embodiment of the integrated gripper  10  could first use the vacuum gripper  13  to lift a single work piece  30  without engaging any of the remaining sheets. Magnetic gripper  25  could then engage the work piece  30  once it has cleared the stack. 
     In the embodiment shown in  FIG. 1 , the integrated gripper  10  includes a part sensor  42 . Integration of a part sensor allows an operator or a control system overseeing the manufacturing process to know whether or not the work piece  30  is, in fact, engaged with the integrated gripper  10 . The integrated part sensor  42  assists with system timing and monitoring, and lets the system determine whether or not backup systems—such as the magnetic gripper  25 —need to be engaged and selective action to be taken to slow or stop the operation. 
     Those having ordinary skill in the art will recognize many possible methods of sensing engagement of the work piece  30 . One embodiment of an integrated part sensor  42  that can be incorporated into the integrated gripper  10  is an inductive proximity switch. A ferrous work piece  30  will cause a voltage change in a coil on the inductive proximity switch of the integrated part sensor  42 , and this voltage change will alert the control system that the work piece  30  is near. 
     An alternative integrated part sensor  42  is a Hall Effect sensor, which is a magnetic sensor that senses changes in the magnetic field caused by engagement of the work piece  30 . Those skilled in the art will recognize other part sensors, such as, without limitation, optical sensors detecting the presence and distance of objects in relation to the gripping end  18 . The integrated part sensor  42  could be located outside of the rigid housing  12 , allowing maximum flexibility of placement; or inside of rigid housing  12 , allowing the integrated part sensor  42  to be fully enclosed and protected from damage or interference. 
     A method of lifting and moving the work piece  30  through a multi-stage manufacturing process is also provided. The integrated gripper  10  is configured to hold the work piece  30  with two different levels of force: the vacuum gripping function (supplied by the vacuum gripper  13 ) is capable of holding the work piece  30  under high acceleration (high loads), and the magnetic gripping function (supplied by the magnetic gripper  25 ) is capable of holding the work piece  30  only at lower levels of acceleration and speed. 
       FIG. 2  shows an embodiment of a method  100  of using an integrated gripper  10  to lift and move the work piece  30  through a multi-stage manufacturing process. The method  100  may, but need not be, used in conjunction with the structure and components of integrated gripper  10 . For descriptive purposes, the method  100  is described with respect and reference to integrated gripper  10 . The method  100  begins at start process  102 , where the vacuum source  22  begins removing air from vacuum chamber  16  and the integrated gripper  10  moves to pick up the work piece  30  using only the vacuum gripper  13 . 
     At decision step  104 , the part sensor  42  checks to see that the work piece  30  is, in fact, engaged. If no work piece is engaged, the system will stop for a pause  105  and then check again, until a work piece  30  is engaged. Often, there is no point in continuing the manufacturing process without a work piece. If the work piece  30  is engaged with the integrated gripper  10 , decision step  106  will determine whether or not the vacuum is operating properly by sensing the relative vacuum being maintained in the vacuum chamber  16 . If the vacuum gripper  13  has sufficient vacuum pressure to hold the work piece  30  at a predetermined level of force, method  100  moves to high speed operation  108 . 
     While the vacuum gripper  13  is fully operational, the method  100  can move the integrated gripper  10  and work piece  30  through the manufacturing process at maximum speeds and acceleration. After method  100  completes its current step in the manufacturing process at high speed operation  108 , decision step  110  will determine whether a further step remains in the manufacturing process or whether the process is complete (a finished work piece  30 ). If further steps are involved in the manufacturing process, method  100  will again verify engagement of the work piece in decision  104  and repeat steps  106 - 110  until no manufacturing steps remain. 
     Once the manufacturing process is complete, an end process  112  will run. In the end process  112 , the work piece  30  might be deposited in an inventory or moved to a transfer point for another manufacturing or assembly process. After releasing the work piece  30 , the method  100  will move the integrated gripper  10  into position for its next cycle  114 , which may be: a repeat of the method  100 , a break for the end of one labor shift and beginning of another labor shift, a break for routine maintenance and inspection, or reconfiguration for a different work piece or different manufacturing process. 
     During each step in the manufacturing process, method  100  will perform decision step  106  to ensure that the vacuum gripper  13  is fully operational. Whenever the system determines that the there is a problem with vacuum gripper  13 —due to loss of power to vacuum source  22  or some other failure that causes vacuum chamber  16  to lose its proper vacuum pressure—magnetic gripper  25  will automatically engage in step  116 . The system will also slow to a low speed operation  118 . 
     Steps  116  and  118  ensure that the work piece  30  is properly held by the integrated gripper  10  while still allowing the manufacturing process to continue (at reduced speed and efficiency) until it is feasible to halt the process to repair or replace the integrated gripper  10 . In this embodiment, reducing the manufacturing process to low speed operation is necessary because the vacuum gripper  25  is not capable of reliably holding the work piece  30  under the greater loads incurred during high speed operation  108 . By using the magnetic gripper  25  as a backup mechanism, the integrated gripper  10  does not require backup mechanical clamps. This can greatly facilitate the flexibility of particular gripping end effectors in grasping many different shaped and sized parts within a certain range, since the limiting nature of the application of fixed mechanical clamping is no longer required. 
     After switching to low speed operation  118 , method  100  continues much as if the vacuum were operational. In decision step  120  (like decision step  110 ) the system determines whether further manufacturing steps are necessary or if the system can proceed to end process  122  (which, except for the lowered speed, is identical to end process  112 ). 
     Once the manufacturing process has ended (and work piece  30  deposited, as described above) following a failure of the vacuum gripper  13 , the system alerts the controller of the manufacturing process in step  124  and enters a maintenance break  126 . This maintenance break  126  may be scheduled to coincide with labor shift change, an inspection and maintenance break, or a break to reconfigure the integrated gripper  10  for a different work piece  30 . 
     During the maintenance break  126 , workers can assess the reasons for failure of the vacuum gripper  13  and either make necessary repairs or replace the integrated gripper  10 . Once the vacuum gripper  13  has been tested and is again operational, the integrated gripper  10  may be moved into position for the next cycle  114 . 
     Those having ordinary skill in the art will recognize alternative embodiments and variations to the method  100  described above. One alternative uses both the vacuum and magnetic gripping functions to actively grip the work piece during high speed operation (similar to steps  106 - 110 ). This adds additional gripping force while the integrated gripping device is fully operational, but retains the ability to switch to solely magnetic gripping for low speed operation and limp-home modes. 
     A further alternative step to method  100  (or alternatives) would allow the whole process to be paused or shut down and the vacuum shut off for an energy savings. This may occur, for example, during a labor shift change that occurs in the middle of the manufacturing process being implemented with the integrated gripper. During this stage, the magnetic gripper would engage to hold the part such that the part may be retained indefinitely until the process is restarted. This step may greatly reduce the energy required to hold and pause the manufacturing process, because a permanent magnet requires far less energy to hold the work piece than a vacuum. 
     While the best modes and other modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.