Mitigating Current At Startup Of Ultrasonics

Abstract

Methods of mitigating current overload of an ultrasonic system having an ultrasonic stack under load at startup are provided. The methods include beginning an ultrasonic cycle in the ultrasonic system having the ultrasonic stack that runs a closed loop phase control through the weld cycle by ramping up the power of the ultrasonic stack under load. During ramping up of the power of the ultrasonic stack under load, a controller lowers the phase to a negative phase. After ramping up the power of the ultrasonic stack under load is complete, the controller raises the phase to 0 degrees and the ultrasonic stack is operating at steady state and with the phase at 0 degrees.

Claims

1. A method of mitigating current overload of an ultrasonic system having an ultrasonic stack under load at startup, the method comprising: beginning an ultrasonic cycle in the ultrasonic system having the ultrasonic stack that runs a closed loop phase control through the weld cycle by ramping up the power of the ultrasonic stack under load; during ramping up of the power of the ultrasonic stack under load lowering via a controller the phase to a negative phase; and after ramping up of the power of the ultrasonic stack under load is complete raising via the controller the phase to 0 degrees and operating the ultrasonic stack at steady state and with the phase at 0 degrees.

2. The method of claim 1, wherein the closed loop phase control comprises a P control, I control, PI control, PID control, State Space Control, Kalman Filter, Sliding Mode control, or Bang Bang control.

3. The method of claim 1, wherein the ultrasonic system is used for welding, cutting, swaging, staking, agitating, cleaning, or drilling.

4. The method of claim 1, wherein lowering the phase includes lowering the phase to a negative phase in the range of 1 degrees to 90 degrees.

5. An ultrasonic system, the ultrasonic system comprising: an ultrasonic power supply for supplying ultrasonic power to an ultrasonic stack under load at startup that runs a closed loop phase control through a weld cycle and for ramping up the power supplied to the ultrasonic stack at the beginning of the weld cycle; and a controller for controlling the phase of the ultrasonic stack, wherein the controller is configured to lower the phase of the ultrasonic stack below 0 degrees when ramping up the power of the ultrasonic stack under load, and wherein the controller is configured to, after ramping up of the power of the ultrasonic stack under load is complete, raise the phase to 0 degrees and operate the ultrasonic stack at steady state and with the phase at 0 degrees for the duration of the ultrasonic cycle.

6. The ultrasonic system of claim 5, wherein the closed loop phase control comprises a P control, I control, PI control, PID control, State Space Control, Kalman Filter, Sliding Mode control, or Bang Bang control.

7. The ultrasonic system of claim 5, wherein the ultrasonic system is an ultrasonic welder, an ultrasonic cutter, an ultrasonic swaging machine, an ultrasonic staking machine, an ultrasonic agitator, an ultrasonic cleaner, or an ultrasonic driller.

8. The ultrasonic system of claim 5, wherein the controller is configured to lower the phase of the ultrasonic stack in the range of 1 degrees to 90 degrees when ramping up the power of the ultrasonic stack.

Description

DRAWINGS

[0020] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0021] FIG. 1 is a diagrammatic view showing a prior art ultrasonic system and prior art control of an ultrasonic power supply that excites a piezoelectric powered ultrasonic stack of the ultrasonic system;

[0022] FIG. 2 is a diagrammatic view showing a power supply having current mitigation during ultrasonic ramp up under load;

[0023] FIG. 3 is a plot showing ultrasonic ramp up under load without overcurrent mitigation; and

[0024] FIG. 4 is a plot showing ultrasonic ramp up under load with overcurrent mitigation using methods according to the present disclosure.

[0025] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0026] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0027] Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term about whether or not about actually appears before the numerical value. About indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by about is not otherwise understood in the art with this ordinary meaning, then about as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. If, for some reason, the imprecision provided by about is not otherwise understood in the art with this ordinary meaning, then about as used herein may indicate a possible variation of up to 5% of the indicated value or 5% variance from usual methods of measurement.

[0028] The following discussion will be with reference to ultrasonic device 100 of FIG. 1, but it should be understood that the following applies to any ultrasonic device used for welding, cutting, swaging, staking, agitation, cleaning, drilling, or any other process that needs ultrasonics and is capable of exhibiting closed loop controls. In this regard, it should be understood that the method of mitigating current overload of an ultrasonic power supply during startup of an ultrasonic stack in accordance with an aspect of the present disclosure as described below differs from methods used in prior art ultrasonic devices and the indication that FIG. 1 is prior art does not mean that the below described method is in the prior art. Further, as noted above, ultrasonic stack 102 may or may not comprise either or both of booster 108 or ultrasonic horn 110.

[0029] As noted above, it is desirable to prevent current overloads of the ultrasonic power supply. But oftentimes with the startup of ultrasonic applications under load, the amplitude of the RMS current increases to a high level, which can result in a current overload of the ultrasonic power supply. Such current overloads of the ultrasonic power supply are known to occur during a startup ramp-up of the ultrasonic power in the ultrasonic stack, and are independent of the RMS voltage. Further, these current overloads are inherent with ultrasonic power supplies that use closed loop controls to maintain a zero phase between the voltage and current. As noted above, there is a countervailing interest to keep this phase at zero.

[0030] The reason for the high current levels can be seen by the following: at steady state, the power consumed by the ultrasonic horn when a force is exerted on the horn is:

PowerA*F*f (1)

[0031] Where:

[0032] A=RMS amplitude at end of ultrasonic horn

[0033] F=force exerted on horn

[0034] f=frequency of ultrasonic horn

[0035] But:

AV*cos() (2)

[0036] Where:

[0037] =phase between I and V

[0038] I=RMS current of ultrasonic power supply

[0039] V=RMS voltage of ultrasonic power supply

[0040] But:

Power=I*V (3)

[0041] So by Equations 1, 2, and 3, the following relationship is seen:

I*VA*F*fV*cos()*F*fPower (4)

[0042] Factoring out the common variable V in equation 4 provides the following:

Icos()*F*f (5)

[0043] As noted above, Equation 5 is independent of the RMS voltage. RMS voltage control alone therefore will not reduce the RMS current when the ultrasonic stack is operating at steady state. Also as noted above, while the ultrasonic horn is doing its processing it is desirable, if not required, to have the phase between the voltage and current at zero. The current consumed at steady state under a given force is a level of current needed to be supplied by the power supply.

[0044] That all said, because a typical ultrasonic horn has a quality factor of greater than about 100 in some applications and in others greater than or equal to about 1000 at steady state, when the energy of the horn is ramping up at startup, the power needed is governed by Equation 1. During ramping up, the power levels are higher than they would be at steady state because the latent energy of the horn must be built up. This means that the current seen in Equation 5 during ramping up is larger than that experienced during steady state operation of the ultrasonic stack and therefore is at a higher level than is needed during steady state operation. This can lead to current overload of the ultrasonic power supply at startup when the horn is under load unless prophylactic measures are taken, such as using multiple power supplies or having an ultrasonic power supply having a current rating higher than necessary at steady state.

[0045] Accordingly, with reference to FIG. 2, providing current mitigation at the startup of ultrasonics is disclosed. A controller, such as electronic control unit (ECU) 206 has control logic that implements RMS converter module 208, phase detector module 210, feedback signal module 212, and phase control module 214 through software, firmware, or the like.

[0046] While ECU 206 is illustratively shown as residing in ultrasonic power supply 204, ECU 206 may reside separately therefrom. Further, it should be understood that any or all of RMS converter module 208, phase detector module 210, feedback signal module 212, and phase control module 214 could be separate modules.

[0047] A voltage sensor 216 is coupled to output of ultrasonic power supply 204 and senses an output voltage of ultrasonic power supply 204, and a current sensor 218 is also coupled to output of ultrasonic power supply 204 that senses an output current of ultrasonic power supply 204. RMS converter module 208 calculates the RMS voltage based on the output voltage detected by voltage sensor 216 and, and RMS converter module 208 also calculates the RMS current based on the output current detected by current sensor 218. Phase detector module 210 detects a phase difference angle between the output voltage and the output current of ultrasonic power supply 204 and this phase difference angle is relayed to the feedback signal module 212 of ECU 206. Feedback signal module 212 instructs phase control module 214 to adjust the phase as warranted. According to some aspects, phase control module 214 adjusts the phase automatically to a phase less than 1 degrees to greater than 90 degrees at the start of an ultrasonic cycle having an ultrasonic stack under load. Once the ultrasonic stack reaches an appropriate power level, the phase control module adjusts the phase to zero.

[0048] By way of example, reference to FIGS. 3 and 4 are made. Turning first to FIG. 3, which illustrates ultrasonic ramp-up under load without overcurrent mitigation, the RMS voltage (Vrms), RMS current (Irms), and phase are plotted as a function of time. During ramp-up of an ultrasonic stack under load, the phase is kept at 0 degrees. The Irms, however, increases to 120%, i.e., at a level 20% greater than is required for steady-state operation. If the ultrasonic power supply is rated just to have 100% of the power needed for steady state operation, a power overload results. Referring to FIG. 4, which illustrates ultrasonic ramp-up under load with overcurrent mitigation in accordance with an aspect of the present disclosure, as with FIG. 3, the Vrms, Irms, and phase is plotted as a function of time. During ramp-up of an ultrasonic stack under load, the phase is reduced to about 30 degrees (e.g., by phase control module 214). This reduction in phase correspondingly reduces the Irms. Once the ultrasonic stack is ramped up to steady state, the phase is returned to 0 degrees (e.g., by phase control module 214). Notably, during ramp up, the Irms does not go above 100%, thereby preventing a power overload. While the example shown in FIG. 4 shows achieving an Irms of 100% by reducing the phase to about 30 degrees, it should be noted that a suitable Irms may be achieved by reducing the phase from greater than 90 degrees to less than 1 degrees, depending on applicable parameters defining what a suitable Irms is for a particular ramp-up of an ultrasonic stack under load.

[0049] As used herein, the term controller, control module, control system, or the like may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; a programmable logic controller, programmable control system such as a processor based control system including a computer based control system, a process controller such as a PID controller, or other suitable hardware components that provide the described functionality or provide the above functionality when programmed with software as described herein; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor. Appropriate closed loop controls include P, I, PI, and/or PID controls; State Space Controls; Kalman Filters; Sliding Mode controls; Bang Bang Controls; and/or any other control that uses feedback to control the phase. When it is stated that such a device performs a function, it should be understood that the device is configured to perform the function by appropriate logic, such as software, hardware, or a combination thereof.

[0050] Spatially relative terms, such as inner, outer, beneath, below, lower, above, upper, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as below or beneath other elements or features would then be oriented above the other elements or features. Thus, the example term below can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0051] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.