Patent Publication Number: US-2006011707-A1

Title: Multiple probe power systems and methods for ultrasonic welding

Description:
RELATED APPLICATION  
      This application is a Continuation-In-Part of pending U.S. application Ser. No. 10/667,035, filed Sep. 22, 2003. 
    
    
     FIELD OF THE INVENTION  
      This invention is directed generally to ultrasonic welding and is more particularly related to systems and methods for providing power to multiple ultrasonic welding probes.  
     BACKGROUND OF THE INVENTION  
      Ultrasonic welding is an efficient technique for joining component parts in manufacturing environments. Applications of ultrasonic welding include the welding of plastic parts and fabrics when manufacturing products such as automobile components, medical products, and hygiene products.  
      Manufacturers who employ ultrasonic welding may use several individual welding devices, or “probes,” in a single manufacturing environment. Individual devices may be customized for particular welds or for use on particular components. It is desirable, from a cost standpoint and also given the motivation to conserve space in a manufacturing environment, to use a minimum of power supplies to power an appropriate number of ultrasonic probes.  
      To achieve maximum power transfer efficiency (of greater than approximately 90%) from an ultrasonic generator to an ultrasonic load, such as a probe, the generator must drive the ultrasonic load at the load&#39;s exact mechanical resonant frequency. Circuitry inside the generator allows the generator drive frequency to track the load resonant frequency, which drifts due to temperature variations and may also be caused by the aging characteristics of the ultrasonic transducer or driver.  
      Powering more than one ultrasonic load from one ultrasonic generator output at one time can cause an overload condition on the output of the generator, because it is not possible to match the resonant frequency of multiple probes exactly. The resonant frequencies of two probes will change over time because different ultrasonic probes age differently over time and the temperature changes they experience will not match over time. Thus, to power multiple probes from one generator output, the probes should be individually switched to the high voltage (typically greater than 1,000 Vrms) generator output. This may be accomplished by using multiple high-voltage relays, with one relay dedicated to each ultrasonic load.  
     SUMMARY OF THE INVENTION  
      According to one embodiment, a multiple probe controller is provided for sequencing control for multi-probe ultrasound welding systems. According to one embodiment of the present invention the multiple probe controller sequencer is integrated into power generating equipment for ultrasonic welding.  
      According to another embodiment of the present invention the multiple probe controller is a compact modular design contained in an independent enclosure providing is the necessary connections to function with and control an ultrasonic welding system.  
      According to yet another embodiment of the present invention an independent master multiple probe controller enclosure mates with a slave multiple probe controller enclosure to add support for the control of additional ultrasound welding probes.  
      According to yet another embodiment of the present invention a multiple probe controller is used in conjunction with an automation controller to provide control signals as required to power a plurality to ultrasonic probes.  
      According to another embodiment of the present invention, a multiple probe power supply and controller allows weld times and weld amplitude levels to be assigned to multiple ultrasonic welding probes. Alternatively or additionally, welds may be specified by the overall weld energy required.  
      Power is provided to multiple ultrasonic welding probes such that only one probe is powered at a time from a single ultrasonic generator, with a change in the powered probe being enabled only after voltage at a first probe decreases to a safe level for a power change.  
      According to another embodiment of the present invention, a system for providing power to more than one ultrasonic welding probe from a single power supply is provided. The system includes a first multiple probe subassembly having a first jack for connection to a first ultrasonic welding probe and a second jack for connection to a second ultrasonic welding probe. The system also includes a second multiple probe subassembly, which has a third jack for connection to a third ultrasonic welding probe and a fourth jack for connection to a fourth ultrasonic welding probe. At least one connector connects the first multiple probe subassembly to the second multiple probe subassembly.  
      According to yet another embodiment of the present invention, a method for providing power to more than one ultrasonic welding probe includes providing a first multiple probe subassembly, a second multiple probe subassembly, and a master control, all housed in a multiple probe controller chassis. The first multiple probe subassembly includes a first jack for connection to a first ultrasonic welding probe and a second jack for connection to a second ultrasonic welding probe. The second multiple probe subassembly includes a third jack for connection to a third ultrasonic welding probe and a fourth jack for connection to a fourth ultrasonic welding probe. The method further includes coupling the first and second multiple probe subassemblies and the master control with at least one connector.  
      According to another embodiment of the present invention, a system for providing power to more than one ultrasonic welding probe from a single power supply is provided. The system includes at least tow multiple probe subassemblies. Each of the at least two multiple probe subassemblies are adapted to provide an ultrasonic signal to a plurality of ultrasonic probes. A master control is coupled to the at least two multiple probe subassemblies, such that the master control is a separate physical device from the at least two multiple probe subassemblies. The master control includes at least one programmable logic component for detecting the power status of each of the plurality of ultrasonic probes and further for generating an ultrasonic welding probe status signal for each of the plurality of ultrasonic probes.  
      According to another embodiment of the present invention, a subassembly is provided. The subassembly includes at least one jack for connecting to an ultrasonic probe. An ultrasonic input is included for receiving an ultrasonic signal. An ultrasonic output is included for transmitting the ultrasonic signal to an ultrasonic input of another subassembly. The subassembly also includes a control input and a control output. The control input receives a control signal from a master control. The control output transmits the control signal to a control input of the another subassembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings:  
       FIG. 1  is a block diagram showing an ultrasound welding system according to one embodiment of the present invention;  
       FIG. 2  is a signal diagram showing timing delays for the provision of ultrasound power to an ultrasound probe;  
       FIG. 3  is a block diagram of multiple probe controller logic according to one embodiment of the present invention;  
       FIG. 4  is a block diagram of programmable logic device operation for a multiple probe controller according to one embodiment of the present invention;  
       FIG. 5  is a signal trace illustrating a power up timing sequence according to one embodiment of the present invention;  
       FIG. 6  is a signal trace illustrating a power failure timing sequence according to one embodiment of the present invention;  
       FIG. 7  is a signal trace illustrating probe relay selection timing, switching probe  2  to probe  1  according to one embodiment of the present invention;  
       FIG. 8  is a signal trace illustrating probe relay selection timing, switching probe  1  to probe  2  according to one embodiment of the present invention;  
       FIG. 9  is a signal trace illustrating ultrasound activation timing according to one embodiment of the present invention;  
       FIG. 10  is a signal trace illustrating ultrasound deactivation timing according to one embodiment of the present invention;  
       FIG. 11  is a state transition diagram for the operation of the multiple probe controller according to one embodiment of the present invention;  
       FIG. 12  is a block diagram showing a master-and-slave construction for a multiple probe controller according to one embodiment of the present invention;  
       FIG. 13  is a front view of ultrasound probe connection panels according to one embodiment of the present invention;  
       FIG. 14   a  is a block diagram showing a chassis housing two multiple probe subassemblies according to one embodiment of the present invention;  
       FIG. 14   b  is a perspective view of the chassis of  FIG. 14   a;    
       FIGS. 15   a - e  are front views of chassis and ultrasonic probe jacks according to various embodiments of the present invention; and  
       FIGS. 16   a - d  are front views of a chassis and ultrasonic probe jacks according to various other embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT  
      Turning now to  FIG. 1 , a block diagram of an ultrasound welding system  10  according to one embodiment of the present invention is shown. An ultrasonic generator  12  contains a multiple probe controller (MPC)  14 .  FIG. 1  shows the MPC  14  implemented as a master MPC unit  15  and a slave MPC unit  16 . Each of the MPC units routes power to a number of ultrasonic probes  18   a - h  via probe connections  20  attached to ultrasonic power jacks  22 . The ultrasonic generator  12  powers ultrasonic probes  18  according to signals received from an automation control system  24 . The automation control system  24  is a type of selector input device that may be used with the present system. Alternatively, manual control of switching to request ultrasound probe selections and to request the activation and deactivation of ultrasound power may be used in some embodiments.  
      Power from the ultrasonic generator  12  is delivered from an ultrasonic power output  26  to an ultrasonic power input  28  provided on the master MPC unit  14 . System outputs  30  of the ultrasonic generator  12  forward signals to automation control inputs  32  of the automation control system  24 , and system inputs  34  of the ultrasonic generator  12  receive signals from automation control outputs  36  of the automation control system  24 .  
      Signal inputs at the automation control system  24  include an MPC ready signal input  38 , an ultrasound power status signal input  40 , and a monitor signal common input  42 . Signal outputs of the automation control system  24  include an ultrasound activation output  44 , and probe selection bit outputs  46 ,  48 , and  50 . While three probe selection bits are shown in the embodiment of  FIG. 1 , more or fewer probe selection bits may be provided, depending on the number of ultrasonic probes  18  to be selected. For example, a fourth probe selection bit output may be provided to allow for selection of up to sixteen probes using a hexadecimal numbering code. The probe selection bits  46 ,  48 , and  50  are binary weighted bits, with bit  0  being the least significant bit and bit  2  being the most significant bit. Using three bits, it is possible to select up to eight different ultrasonic probes. This method has the advantage of making it impossible for the automation control system  24  to select two probes simultaneously, as it is desirable to prevent activation of more than one probe selection relay at a time. A common (ground) connection  52  is also provided between the automation control system  24  and the ultrasonic generator  12 . The functions of each of these signals will be understood upon reference to their descriptions, below.  
      Ultrasonic probes  18  for use with the present invention may include any type of ultrasound welding probe, including ultrasound welding probes optimized with tools for particular ultrasound welding applications. Ultrasound weld time, which may be controlled by a timer within the automation control system  24  or by a weld time controller provided within the ultrasonic generator  12  may be controlled on the basis of weld time, or may measure ultrasonic power and integrate watt-seconds to result in a particular amount of weld energy for the particular weld. According to one embodiment, the automation control system  24  may select which probe  18  will be used for a weld time and can also control the duration of a weld by sending activation signals from the ultrasound activation output  44  to the ultrasonic generator  12 . An ultrasound status signal output may be supplied to the automation control system  24  to allow the automation control system  24  to time the actual duration of ultrasound output if very accurate weld times are required.  
      A weld timer within the ultrasonic generator  12  may have user-programmable windows to define acceptable welded parts. For example, the system could be programmed to weld parts by energy and the ultrasonic welding system  10  may be set to a weld energy of 500 Joules. A weld controller within the ultrasonic generator would control the ultrasound generator  12  to apply ultrasound until 500 Watt seconds of energy had been applied to the part, but a secondary time window or limit may be programmed to detect a malfunction in the process. In the example above, it might be typical for the part to draw 500 Watts of ultrasonic power when welding is correctly achieved, which would result in approximately a one-second cycle time. A time window may be programmed such that if the programmed energy level is achieved outside a pre-set time window (for example, in less than 0.5 second or greater than 2 seconds), the part may be flagged as a bad or suspect part and in some instances automation equipment could be used to sort the part into an appropriate part bin.  
      The ultrasonic welding system  10  allows for the provisioning of ultrasound power from the ultrasonic generator  12  to one ultrasonic probe  18  at a time. An MPC ready signal from the MPC  14  informs the automation control system  24  as to when it is possible to change the selection bits  46 ,  48 , and  50  for a new ultrasonic probe  18  following the termination of power to another ultrasonic probe  18  and a ring-down period during which the ultrasonic probe stops vibrating.  
      Referring now to  FIG. 2 , a timing diagram for an ultrasound welding system  10  is according to one embodiment of the present invention is shown. An MPC ready status signal  54  is sent from the MPC  14  from the system outputs  30  of the ultrasonic generator to the MPC ready signal input  38  of the automation control system  24 . The MPC ready status signal  54  provides an indication of when the MPC  14  is ready to provide power to a different ultrasonic probe  18 . An ultrasound power status signal  56  is sent from the system outputs  30  of the ultrasonic generator  12  to the ultrasonic status signal input  40  of the automation control system  24 . A probe selection signal  58 —actually a graphical depiction of the outcome of the probe selection bits-shows the change over time of probe selection by the automation control system  24 . An ultrasound activation signal  60  is sent from the ultrasound activation output  44  of the automation control system  24  to the system inputs  34  of the ultrasonic generator  12  and indicates when the automation control system  24  is attempting to initiate the provision of ultrasound power to the selected probe  18 . An ultrasound voltage output signal  62  shows voltage in the probe connection  20  of the activated probe.  
      At the beginning, time t 0 , of the time shown in  FIG. 2 , probe number one is selected and no power is being provided to the probes. Further, because the MPC ready status signal  54  is set to its ready state—low, as shown—the automation control system  24  is free to select another probe to power. A short time after t 0 , at t 1 , the probe selection is changed to select probe number five, as shown by the probe selection signal  58 . Synchronous logic within the multiple probe controller  14  requires a delay between the selection of a new probe and the activation of ultrasound power. For example, in one embodiment synchronization within the multiple probe controller  14  requires that the automation control system  24  provide a minimum 40 ms delay for proper operation between t 1 , when probe number five is selected, and t 2 , when the ultrasound activation signal  60  changes from its high, inactivated state to its low, activate state. Substantially immediately upon the activation of the ultrasound activation signal  60 , the MPC ready status signal  54  changes from its low, ready state to its high, not-ready state. A short time later, at t 3 , the ultrasound power status signal  56  changes from its high state, showing that ultrasound power is not being provided, to its low state, showing that ultrasound power is being provided. The time delay between t 2  and t 3  is due to the fact that the MPC  14  does not operate on the same synchronous logic as the automation control system  24 . The initiation of ultrasonic power occurs according to the synchronous logic of the MPC and is not directly controlled by the automation control system  24 .  
      Ultrasound power activation continues until t 4 , when the ultrasound activation signal  60  changes from its low, activation state to its high, inactivated state. Substantially simultaneously with this state transition, the ultrasound power status signal  56  changes from its low state, indicating that ultrasound power is being provided, to its high state, indicating that the provisioning of ultrasound power has been terminated. The ultrasound power status signal  56  changes simultaneously with a deactivation signal from the ultrasound activation signal  60  because deactivation signals do not proceed through the synchronous logic of the MPC  14 .  
      Following t 4 , a ringdown period occurs in the ultrasound voltage output signal  62 , until t 5 . The ringdown time is variable based on the characteristics of the particular probe  16  being powered-down, including characteristics such as ultrasonic stack characteristics and clamping pressure of the probe. Following the ringdown period, at t 6 , the MPC ready status signal changes from high (not ready) to low (ready), indicating that probe selections may be accepted by the MPC unit(s)  14 . Again, the time delay between t 5  and t 6  is due to the asynchronous relationship between the ringdown time and the synchronous logic of the MPC  14 . Between t 2  and t 6 , any changes in the probe selection signal  41  will be ignored by the master MPC  15  or slave MPC  16  because the MPC ready status signal  54  is set to high (not ready).  
      Turning now to  FIG. 3 a  block diagram schematic of a multiple probe controller  14  according to one embodiment of the present invention is shown. A programmable logic device  64  implements digital logic for the MPC  14 . The circuitry of the multiple probe controller  14  is powered by one or more control power and conditioning circuits  66  which, according to one embodiment of the present invention, accept input power from a power supply conduit  68  and supplies a nominal 24 volts DC to a voltage sense circuit  70  and 12 volts DC to a 5 volt regulator circuit  72 . Local power conditioning filter capacitors (not shown) are included on the control power supply outputs so the functionality of the relay control circuitry—described in further detail below—is not compromised due to any line power variations or even total power outages.  
      The regulator circuit  72 , in turn, powers the digital control logic components. The regulator circuit  72  is connected to ground  74 . The control power and conditioning circuits  66  also contain hold-up capacitors to maintain sufficient power during power failure or brown out conditions to ensure safe control of transition states. Power is provided to ultrasonic probes via relays  76 . The sense circuit  70  provides the programmable logic device  64  with input to detect a malfunction of the relay control voltage which will require the inhibition of ultrasound welding voltage to protect the contacts of relays  76 . The relays  76  receive ultrasound power from the ultrasonic power input  28  and route the power to ultrasound probes  16  based on which probe has been selected. According to one embodiment of the present invention the relays  76  have a maximum rating of 5000 Vrms @ 5 A. Power-fail interface components  78  include an external module with circuitry that monitors the magnitude of input AC power and provides a power fail signal  80  if the AC line level is less than an under-voltage trip setting.  
      The programmable logic device  64  receives a timing signal from a clock  82  for timing and state transitions. According to one embodiment, the clock  82  runs at a rate of approximately 32 kHz. A hex buffer  84  receives user inputs  86  and probe status inputs  88 , which according to one embodiment are shifted down to a 5 volt logic level for the programmable logic device  64 . The user inputs  86  may be input into the system inputs  34  of the ultrasonic generator  12 , as shown in  FIG. 1 , and may be inputs from an automation control system  24 . The probe status inputs  88  route the ultrasound status signal  56 , shown in  FIG. 2 , from the ultrasonic generator  12  to the multiple probe controller  14 . In the embodiment shown in  FIG. 1 , the ultrasound status signal  56  is routed within the chassis of the ultrasonic generator  12  to the master multiple probe controller unit  15 , which is provided within the chassis of the ultrasonic generator. The ultrasound status signal is used by the multiple probe controller state logic  122  (discussed below with respect to  FIG. 4 ) and is also used to control the state of light-emitting diode (LED) indicators in LED driver logic  164  (also discussed below with respect to  FIG. 4 ). In the embodiment shown in  FIG. 3 , five connections are made between the hex buffer  84  and the programmable logic device  64 . Connections for selection bit signals zero, one, and two  90 ,  92 , and  94  control which ultrasound probe is selected for operation. The ultrasound power status signal  56  indicates the status of ultrasound probes to the programmable logic device  64 . The ultrasound activation signal  60  signals the programmable logic device  64  to initiate ultrasound probe operation.  
      In the embodiment of  FIG. 3 , the programmable logic device  64  outputs control signals to a relay coil driver circuit  96 . In the shown embodiment, the programmable logic device  64  outputs the control signals to the relay coil driver circuit  96  through relay coil driver control signal conduits  98 . The relay driver circuit  96  drives outputs through relay control conduits  100  to control relay circuits  76 , which in turn provide power from an ultrasound power input  28  to ultrasound probes  16   a - 16   d . In the embodiment shown in  FIG. 3 , the relay coil driver circuit  96  is also equipped to provide relay coil driver control signals for four additional ultrasound probes, as shown by the additional relay control signal conduits  100 . The relay circuits to control the additional probes may be provided within the same cabinet as the circuitry shown in  FIG. 3 , or they may be provided in a separate housing.  
      Two voltage fault devices provide inputs to the programmable logic device  64 . The coil driver fault detection circuit  102  detects faults within the relay coil driver circuit  96  and checks that only one relay coil is activated. A fault condition is signaled if a relay coil driver failure—i.e., a short—occurs that would activate two or more probes simultaneously. An ultrasound voltage sense circuit  104  samples the ultrasound welding voltage at the relays  76  to detect when the ultrasound welding voltage reaches or is at a safe, (i.e., near zero) level. According to one embodiment, the ultrasound voltage sense circuit  104  monitoring the magnitude of the ultrasound voltage and having a voltage trip point set to less than approximately 24 Vac. The output of the ultrasound voltage sense circuit  104  is similar to the ultrasound status signal  56 , shown in  FIG. 2 , with the output of the ultrasound voltage sense circuit  104  remaining active (i.e., in an ultrasound-on state) longer by an amount equal to the ring-down time for an ultrasonic probe.  
      In conjunction with the control of the relay coil driver circuit  96 , the programmable logic device  64  also outputs indicator signals to an LED driver circuit  105  which in turn drives indicator LEDs  106   a - d . According to one embodiment of the present invention, the indicator LEDs  106  are bi-color LEDs. According to one embodiment, the LEDs  106  may illuminate green when the corresponding probe channel is selected and change to red when the ultrasound voltage is activated. If additional probes are implemented then an additional driver circuit  105  and bi-color LEDs  106  may be used.  
      The programmable logic device  64  also outputs signals to an open collector driver  108  which, in turn, forwards an ultrasound activation inhibit signal  110  to an ultrasound activation inhibit output  112 . Another output to an inverting buffer  114  supplies a multiple probe controller ready signal output  116 , which becomes true (on, sinking current) when control changes can be accepted and false (off, open) when control changes will be ignored. Thus, a disconnected cable sends a not ready (false) signal to the multiple probe controller.  
      Turning now to  FIG. 4 a  functional block diagram showing the logic of a programmable logic device  64  of  FIG. 3  according to one embodiment of the present invention is illustrated. The programmable logic device  64  is clocked by a clock divider  118  which provides an internal clock from the 32 kHz clock input  120 . The multiple probe controller state logic block  122  receives an ultrasound voltage sense signal from the ultrasound voltage sense circuit  104  at an ultrasound voltage signal input  124 , a power fail signal  80  from the power fail interface components  78  at a power fail signal input  126 , a coil driver fault signal at a coil driver fault signal input  128  from the coil driver fault detection circuit  102 , and the ultrasound power status signal  56  from the probe status inputs  88  at an ultrasound power status signal input  130 , and is synchronously controlled by the internal clock. The multiple probe controller state logic block  122  also outputs the multiple probe controller ready signal  54 , indicating that the MPC  14  is ready to accept ultrasound probe change instructions, at a multiple probe controller ready signal output  132 . The multiple probe controller state logic block  122  also supplies a master reset signal from a master reset output  134 , provides an ultrasound enable signal from an ultrasound enable output  136 , and accepts an ultrasound activation inhibit input signal at an ultrasound activation inhibit input  138 . The ultrasound activation inhibit signal  110  originates at the logical ultrasound activate inhibit output  140  of the ultrasound activation control logic  142 . Clock synchronization enabling signals travel through clock synchronization connections  144 , under-voltage reset connections  146 , and clock reset connections  148 .  
      Probe selection inputs through which a user or an automation control system  24  chooses which ultrasonic probe to operate are clocked and latched by a synchronous latch  150 . In the embodiment shown in  FIG. 4 , the synchronous latch  150  accepts selection inputs at selection bit inputs  152 ,  154 , and  156 , respectively corresponding to selection bits zero, one, and two, which in turn are sent via selection decoding conduits  158  to a 3-to-8 line decoder  160 . This logic is used to select one of 8 probes with 3 input control bits and according to one embodiment makes it impossible to select more than one probe simultaneously. In the embodiment of  FIG. 4 , the decoder  160  outputs probe selection signals to the relay coil driver logic  120  and the LED driver logic  162 . The multiple probe controller state logic block  122  is responsible for controlling the ultrasound activation logic in response to timing state considerations (as shown  FIGS. 2 and 5 - 10 ) and the various voltage sensing inputs. The relay coil driver logic  162  generates relay control signals input into the relay coil driver circuit  96  (shown in  FIG. 3 ), and the LED driver logic  164  generates LED control signals input into the LED driver circuit  105 . The ultrasound activation control logic  142  generates the ultrasound activation inhibit signal  110  (shown in  FIG. 3 ).  
      In the embodiment of  FIG. 4 , the synchronous latch  150 , the decoder  160 , the clock divider logic  118 , and the ultrasound activation control logic  142  are all resettable via a master reset conduit  166  which originates from the multiple probe controller state logic  122  and enables a centralized reset of the ultrasound controller. The synchronous latch  150  and the ultrasound activation control logic  142  receive clock synchronization signals from a synch clock output  168  of the clock divider  118 . The ultrasound activation control logic  142  accepts the ultrasound activation signal  60  at an ultrasound activation input  170 , accepts the ultrasound enable signal from the ultrasound enable signal output  136  of the MPC state logic  122 , and also generates an ultrasound activation inhibit signal  110  at the ultrasound activation inhibit signal output  140 . The ultrasound activation inhibit signal  110  is sent from the ultrasound activation inhibit signal output  140  to the ultrasound activation inhibit signal input  138  of the MPC state logic  122 .  
      The master and slave multiple probe controllers  15  and  16  operate to monitor ultrasound probe status and to enact probe status changes requested by users of the system or by an automation control system  24 . The signal traces that follow illustrate the operation of an ultrasound welding system according to some embodiments of the present invention.  
      Referring now to  FIG. 5 , a signal trace of a power-up timing sequence according to one embodiment of the present invention is shown. Time is displayed along the x-axis, with each dotted interval representing a 20 ms interval. The power-up timing sequence is initiated when an ultrasound welding system is powered on. During power up and reset conditions, the multiple probe controller  14  initiates a master reset signal, deactivates all relay contacts, and inhibits the synchronous clock. In the embodiment shown in  FIG. 5 , the synchronous clock signal trace  172  shows that the synchronous clock, operating in this embodiment at a rate of approximately 30 Hz, begins oscillating approximately 60 ms after a master reset signal  174  switches from its reset state, shown by a high signal, to its non-reset state, shown by a low signal. The multiple probe controller-ready status signal  54  switches to its low, or ready, state approximately 45 ms after the master reset signal  174  switches from its high, or reset state, to its low, non-reset state. In the embodiment shown in  FIG. 5 , the master reset signal  174  stays in the high state for greater than 40 ms after powerup before switching to the low, non-reset state. When the synchronous clock signal  172  is enabled, a first relay contact signal  176  changes from its low, off state, to its high, on state, enabled by the first synchronous clock rising edge. At this point, the relays  76  have received the signal to activate the first relay to connect the ultrasound power input  28  to the first ultrasound probe  18   a , as shown in  FIG. 3 .  
      Referring now to  FIG. 6 , a signal trace of a power-failure timing sequence according to one embodiment of the present invention is shown. In the signal trace of  FIG. 6 , each dotted-line time interval is approximately 200 ms. During a power failure, the contacts of an active relay should remain operable until the ultrasound voltage level drops to a safe level.  FIG. 6  illustrates the timing sequence when an input power failure occurs during a welding cycle in which an ultrasound output is activated. In the embodiment shown in  FIG. 6 , an ultrasound voltage  178  at an ultrasound probe is on at the beginning of the displayed time. A ring-down signal  180  is high at the beginning of the displayed time, in a non-ring-down state. A power fail signal  80  is low, indicating no power failure. A relay contact monitor signal  182  is high, showing that a relay  76  corresponding to an ultrasonic probe is activated. Upon power failure, about 500 ms after the start of the waveform capture of  FIG. 6 , the power fail signal  80  switches to high, indicating a power failure has occurred. The ultrasound voltage output  178  decays to near zero volts in approximately 350 ms after the power failure. The ring-down signal  180  goes low to indicate a ring-down status during which the power to the ultrasound probe is decaying to a safe level, and then switches back to a logic high and remains high for about 650 ms before the local supply voltage collapses on the ultrasound voltage sense circuit  104 , shown in  FIG. 3 . The ring-down signal functions normally, with about 600 ms of power supply hold-up time margin for ultrasonic stacks or probes that have a longer ring-down time characteristic. A relay contact monitor signal  182  indicates that a relay is closed (high), which is the normal state during a weld cycle. The relay contact monitor signal  144  remains high throughout the power failure, showing that the relay contact remains closed for approximately 600 ms after the ring-down time, until the relay coil voltage collapses.  
      Referring now to  FIG. 7 a  signal trace of a probe relay selection timing sequence according to one embodiment of the present invention is shown. The multiple probe controller ensures that the selection of a new active relay—and therefore, a new welding probe—is accomplished in a clocked and synchronized manner. A synchronous clock signal trace  172  is shown in this embodiment operating at approximately 32 Hz. When the probe select bit zero signal  92  switches from low, corresponding to the selection of a second ultrasonic probe  18   b , to high, corresponding to the selection of the first ultrasonic probe  18   a , asynchronously about 10 milliseconds before the synchronous clock edge, a first relay switches on to provide power to the first ultrasonic probe as shown by the first relay signal  184  and a second relay switches off simultaneously, as shown by the second relay signal  186 , at the next positive-going synchronous clock edge. The synchronous clock signal  172  is inhibited (off) when ultrasound power is switched on, so relay switching changes are not possible without the clock because relay switching changes are linked to clock state changes. During this time, signal changes on the probe selection inputs are ignored.  
      Referring now to  FIG. 8 a  signal trace of a probe relay selection timing sequence according to one embodiment of the present invention is shown. In the embodiment shown in  FIG. 8 , a synchronous clock signal  172  operates at approximately 32 Hz. The probe selection bit zero signal  92  as received by the multiple probe controller  14  from a user selection device or from an automation control system  24  is also shown. In the signal trace of  FIG. 8 , a high signal for selection bit zero corresponds to the selection of a first ultrasound probe, and a low signal for selection bit zero corresponds to selection of a second ultrasound probe. When the probe selection bit zero signal  92  changes from its high state, corresponding to the selection of a first ultrasound probe, to a low state, corresponding to the selection of a second ultrasound probe, the first relay contact signal  184  changes from an activated or high state to a deactivated or low state on the next upward-going edge of the synchronous clock signal  172 . A second relay contact signal  186  changes from a deactivated or low state to an activated or high state at the same upward-going edge of the synchronous clock signal  172 . In this particular example, there is an asynchronous delay time of about 25 ms from the change of the probe select bit signal  92  to the rising edge of the synchronous clock  172  that initiates the relay selection change. It is to be understood that while changes are activated on upward-going clock edges in the embodiment shown in  FIG. 8 , in other embodiments changes may be activated on downward-going clock edges as may be desirable for design considerations.  
      Referring now to  FIG. 9 , a signal trace of an ultrasound activation timing sequence according to one embodiment of the present invention is shown. This figure shows the ultrasound power activation synchronous timing sequence used to activate ultrasound power to a probe that has been previously selected. While in the shown embodiment the probe selection logic, shown in  FIGS. 7 and 8 , uses positive-going clock edges of the synchronous clock to switch states and select a different relay, the ultrasound activation logic, illustrated in  FIG. 9 , uses the negative-going edge of the synchronous clock for activation.  
      In  FIG. 9 , the time axis shows 5 ms for every dotted interval. A synchronous clock signal  172  shows the synchronous clock operating at approximately 32 Hz. The ultrasound activation signal  60  is high when no activation request is being made and low when an activation request is made. The ultrasound activation signal  60  entering into the MPC logic is asynchronous with the MPC logic and may occur at any time. The ultrasound activation inhibit signal  110  is synchronous with the MPC logic and it delays activation of ultrasound power until the first negative clock edge occurs. For example, in  FIG. 9 , there is approximately a 25 ms delay from the state change of the ultrasound activation signal  60  until the first negative clock edge occurs, which is when the ultrasound activation inhibit signal  110  switches to its high (active or enabled) state at which point ultrasound power may be supplied, as shown by the ultrasound power status signal  56 , which switches to its low state to show that power is on.  
      To illustrate the synchronous logic safeguards, suppose an automation control system  24  changed the probe selection bits at the same instant that the ultrasound activation signal  60  changed. The new probe relay would be selected on the first positive-going clock edge, as shown in  FIGS. 7 and 8 . According to one embodiment, the activation time specification for the relay circuits  52  (shown in  FIG. 3 ) is a maximum of 5 ms, so the relay contacts should be closed for at least 10 ms before the negative-going clock edge activates ultrasound output through the selected relay to the selected ultrasonic probe. Activation of ultrasound power and changing probe selection bits simultaneously is not a recommend procedure in this embodiment, because if a negative-going clock edge occurs first, the probe selection bits will not have a positive-going clock edge to effect the probe selection. No positive-going clock edge would be encountered in this case because the synchronous clock signal  172  is inhibited when ultrasound power activates. For proper operation, an automation control system  24  receives an MPC ready status indication at the MPC ready signal input  38  (shown in  FIG. 1 ). Upon receipt of an MPC ready status indication, the automation control system  24  can select the desired probe using the probe selection bit outputs  46 ,  48 , and  50  (shown in  FIG. 1 ), then wait at least 40 ms before switching the ultrasound activation signal  60  on to start the welding cycle.  
      In order for an ultrasound activation request from an ultrasound sequencing device or a user to be acted upon, the activation inhibit signal  110  must be enabled, in its active high state. This allows activation of an ultrasound voltage output only via the synchronous logic circuitry. Referring to  FIG. 9 , the ultrasound activation signal  60  switches low to signal a request to initiate a weld cycle. The ultrasound activation inhibit signal  110  switches from a low, ultrasound power disabling state, to a high, ultrasound power enabling state on the next negative synchronous clock edge. This change disables the synchronous clock during the weld cycle. An ultrasound power status signal  56  switches from high, indicating no ultrasound power is being provided, to low, indicating that ultrasound output is being provided for the weld cycle.  
      Referring now to  FIG. 10 , a signal trace of an ultrasound deactivation timing sequence according to one embodiment of the present invention is shown. The ultrasound deactivation timing sequence handles the power-down logic for an ultrasound probe and ensures that power will not be supplied to a newly-selected ultrasound probe until operation and power consumption by an operating ultrasound probe has ceased. The synchronous clock signal  172  shows that the clock is not operational while the MPC ready status signal  54  indicates the multiple probe controller is not prepared to provide power to a newly-selected ultrasound probe. When the ultrasound activation signal  60  switches from low, indicating that an ultrasound probe is activated, to high, indicating that power to the ultrasound probe has been switched off, the ring-down status signal  181  switches from low, showing that no ring-down is in effect, to high, indicating that the ultrasound probe that is being disabled is in a ring-down state during which the ultrasound probe is allowed to stop vibrating and the ultrasound voltage reaches a safe level for probe selection changes to occur. The ring-down status signal  181  shown in  FIG. 10  is captured from a ring-down signal test point available on a master circuit board of a multiple probe controller. In contrast, the ring-down signal  180  of  FIG. 6  is captured on an output pin directly on the programmable logic device  64 , shown in  FIG. 3 . Though in the examples given the logics of these outputs are inverted from one another, they are derived from the same output signal of the programmable logic device  64 . In the embodiment shown in  FIG. 10 , the ring-down status signal  181  activates for about 90 milliseconds after the deactivation of the ultrasound voltage and prevents any further ultrasound voltage output or probe switching during that time. The multiple probe controller ready status signal  54  continues in the not-ready state (high) until after the ring-down is over and then the synchronous clock  172  begins to function after the multiple probe controller ready status signal  54  switches to its low (ready) state. In the illustrated embodiment, ring-down signals are determined based on signals generated by the ultrasound voltage sense circuit  104 , shown in  FIG. 3 .  
      The use of synchronous digital logic eliminates nearly all the timing requirements that the automation control system  24  must observe. According to some embodiments, the only timing requirement is that the probe selection must occur (when the multiple probe controller  14  is ready) at least a set time—for example, 40 ms—before ultrasound power is activated. The synchronous logic of the multiple probe controller  14  does introduce some timing uncertainty occurring occurs with the external ultrasound activation signal, which is asynchronous to the internal logic in some embodiments. Using an internal (integrated) weld timer will allow for synchronized logics and eliminate this timing uncertainty. Turning now to  FIG. 11 , a state transition diagram is illustrated which shows the general sequence of events with respect to the aforementioned signal traces. Upon powerup or reset, as shown at block  188 , transition is made to the enabled state at block  190 , in which welding is inhibited but a probe relay selection can be made. This state is shown in  FIGS. 7 and 8 , as discussed above. When the probe relay selection is made, transition is made to the activate state, shown at block  192 , as illustrated above at  FIG. 9 , followed by a transition to the welding state  194  which is represented by the final section of the signal trace of  FIG. 9 . When the weld duration is complete, transition is made to the deactivate state  196  (as shown in  FIG. 10 ) until the ultrasound voltage is at a safe level such that transition can be made to the enabled state  190  to continue the probe selection and welding cycle. If the power fails or is shut down transition is made to the power fail state  198 , as shown in  FIG. 6 , until a power up or reset occurs.  
      An alternative embodiment of the present invention, in which a separate multiple probe controller chassis  200  is connected to a compact ultrasonic generator  202 , is shown in  FIG. 12 . The multiple probe controller chassis  200  receives ultrasound power from the generator  202  and receives and sends control signals at an MPC interface input/output  204 , which is connected to an ultrasonic generator MPC interface input/output  206 . System signals from an automation control system  24  are received at system inputs  208  of the ultrasonic generator  202  and system signals are sent from the ultrasonic generator  202  to the automation control system  24  from system outputs  210 . Ultrasound power is routed from an ultrasound output  212  of the ultrasonic generator  202  to an ultrasound input  214  of the multiple probe controller chassis  200 . A master multiple probe controller  15  and two slave multiple probe controllers  16  and  17  are provided to route power to a total of twelve ultrasonic probes  18 . While four ultrasonic probes  18  have been shown connected to the master multiple probe controller  15  and to each of the slave modules  16  and  17 , it is to be appreciated that more or fewer ultrasound probes may be connected to each module as required by particular implementations of the present invention. Further, more than two slave modules may be connected to a single master multiple probe controller  15 , either through direct connections to the master multiple probe controller, or through downstream links to intermediate slave modules.  
      Ultrasonic probes may be connected to multiple probe controllers and slave modules according to the present invention via ultrasonic probe connection panels. Turning to  FIG. 13 , a master ultrasonic probe connection panel  216  and a slave ultrasonic probe connection panel  218  according to one embodiment of the present invention are shown. The master ultrasonic probe connection panel  216  has four ultrasound probe jacks  22   a - d  and four associated bi-color LEDs  220   a - d . The slave ultrasonic probe connection panel  218  has four ultrasound probe jacks  22   e - h , which connect to ultrasound welding cables and four associated bi-color LEDs  220   e - h , which indicate the working status of each jack.  
      Turning now to  FIGS. 14   a  and  14   b , another embodiment of the present invention will be described. As shown, a multiple probe subassembly chassis  300  is illustrated. In the embodiment illustrated in  FIG. 14   a , the chassis  300  includes two multiple probe subassemblies  316 ,  318 . The two multiple probe subassemblies  316 ,  318  are inserted into channels  316   a ,  318   a  ( FIG. 14   b ). The multiple probe subassemblies  316 ,  318  connected to a pair of ultrasound outputs  320   a ,  320   b ,  320   c ,  320   d , which are in turn coupled to ultrasonic probes (not shown).  
      The multiple probe subassemblies  316 ,  318  are connected via ultrasonic connectors  322   a ,  322   b  and a control signal connector  323 . The first ultrasonic connector  322   b  provides an ultrasonic signal and the second ultrasonic connector  322   a  provides ground. The control signal connector  323  provides the control signals. The ultrasonic input connector  324  conducts the ultrasonic signal from a generator, such as the generator  24  of  FIGS. 1 and 12 . The ultrasonic signal powers the ultrasonic probes. The master control  326  provides control signals to the multiple probe subassemblies  316 ,  318  controlling how the ultrasonic signal is routed. In other words, the master control  326  tells the multiple probe subassemblies  316 ,  318  to which probe the ultrasound signal should be sent.  
      The master control  326  is connected to an input connector  328  that receives the control signals from a control signal generator (not shown). The control signal generator interface circuitry may be located in the same housing in an integrated packaging configuration (as shown in  FIG. 1 ) or the control signal generator may be located in a an external housing (as shown in  FIG. 12 ). Power is provided to ultrasonic probes via relays  330  as described above in any of the methods described above in reference to  FIGS. 1-13 .  
      The subassemblies  316 ,  318  are designed so that they can be interconnected in a daisy-chained configuration. The daisy-chain configuration allows both the control signals and the ultrasonic signals that are input into one subassembly to be passed onto the next subassembly. The daisy-chaining feature eliminates the need for including programmable logic devices in each subassembly and allows a “building block” assembly approach. Not only does this keep manufacturing costs down, it enables many different assembly configurations and easier troubleshooting.  
      Daisy-chaining, or using the multiple connectors  322   a ,  322   b , to connect the multiple probe subassemblies  316 ,  318 , both ultrasonic signals and control signals may be transmitted to the multiple probe subassemblies  316 ,  318  without the need for multiple ultrasonic inputs and/or multiple master controls  326 . This keeps the cost of manufacturing down and allows users to add additional multiple probe subassemblies to the system if needed. Also, if one of the multiple probe subassemblies  316 ,  318  malfunctions or is not working properly, it can be easily replaced.  
      In the embodiment illustrated in  FIGS. 14   a  and  14   b , the multiple probe subassemblies are illustrated as being in two channel increments and the chassis includes two subassemblies. However, one of the advantages of the current design allows end-users a choice of the number of multiple probe subassemblies. In one embodiment, a single chassis  340  may be used. As shown, the single chassis  340  ( FIGS. 15   a - e ) comes in a variety of sizes, housing anywhere from two to eight subassemblies (and therefore allowing up to sixteen ultrasonic probes to be used). The single chassis  340  may be compliant with rack mounted chassis dimension standards, which allows a user to stack multiple single chassis  340  in a rack, making storage easy.  
      In another embodiment, a chassis  350   a ,  350   b ,  350   c ,  350   d , shown in  FIGS. 16   a - d , may house up to eight multiple probe subassemblies  316 ,  318 , allowing for sixteen ultrasonic probes. An appropriately sized escutcheon plate  352   a ,  352   b ,  352   c ,  352   d  will cover the stacked modules for the various sizes. In the embodiment shown the escutcheon plate  352  is larger. Smaller systems with fewer channels could be used in a stand-alone bench mounted chassis, if rack mounting is not desired.  
      In the dual row chassis  350   c ,  350   d , the subassemblies can be assembled two tiers high to fit inside an industrial automation equipment enclosure (typically a Hoffman brand box) that is at least about 12 inches deep. Special Hoffman box escutcheon mounting plates  352   c ,  352   d  can be designed for one tier or two tier high systems.  
      While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.