(1) Technical Field
The present invention relates to static neutralizers, which are designed to eliminate or minimize static charge accumulation of an object. These static neutralizers compensate the static charge by generating bipolar air, or in some instances gas, ions and delivering these air or gas ions to a charged object.
(2) Background Art
A static neutralizer is commonly used to remove unwanted or destructive electro-static potential from a charged object, named “target”. Generally, a static neutralizer employs a set of electrodes, sometimes referred to as emitters, ionizing electrodes or corona electrodes, that each have a shape suitable for generating ions by corona discharge when a voltage, named “ionizing voltage”, of sufficient magnitude exceeds a corona on-set threshold voltage, named “corona threshold”. A common ionizing electrode shape includes a long thin cylindrical shape, such as a wire, or an end portion having a small tip radius or a sharp point.
These emitters are positioned generally near the target so that most of the ions created during corona discharge neutralize the charge held by the target rather than be lost to recombination or grounding. One common approach for generating ions includes oscillating or pulsing the ionizing voltage so that it equals or exceeds the corona threshold in both positive and negative polarities, creating a set of ions that includes positive ions and negative ions. A mix of ions that includes ions of opposite polarity is sometimes referred to as a bipolar ion cloud or bipolar ions. These ions may be formed from molecules provided by a gas or a mix of gases, such as air. If these ions are created in an environment filled with air, these ions are sometimes referred to as air ions.
To efficiently and effectively neutralize a target, much effort is made to generate an optimal balance of positive and negative ions. The difference between the number of positive ions and negative ions reaching the target is commonly referred to as ion balance, and this ion balance is typically set prior to first use of the static neutralizer by the end user. However, the ion balance of a static neutralizer is affected by many factors and may change overtime. For example, the emitters may accumulate debris due to air or gas borne contaminants, or the emitters may degrade or erode. Either or both of these conditions may cause the positive ion balance, the negative ion balance or both to change from their original settings. This change in ion balance, named ion balance drift, if left uncorrected, may drift out of a specified voltage range, disrupting the optimal ion balance and decreasing the efficiency of the static neutralizer.
Ion balance can usually be restored by removing or cleaning debris from the contaminated ionizing electrode. However, this approach is less than optimal since it requires the static neutralizer to be placed out of operation during cleaning, which may interrupt production and cause added expense and delay.
Another solution includes using two power supplies to respectively generate positive and negative ions, measuring the currents between each power supply and earth ground, respectively, and using these measured currents to determine the positive and negative ion output of the static neutralizer. When air ions are produced and transported to a target or to the reference electrode, the power supply that provided the corona voltage loses that same quantity of charge, resulting in a current of the same polarity flowing from ground to the ground rail of the power supply power bus if it is a positive current, or from the ground rail of the power supply power bus to ground if it is a negative current.
Measuring the currents between ground and the positive power supply and between ground and the negative power supply was a successful prior art approach, providing that there were separate positive and negative emitters. For simplicity, these currents may be hereinafter referred to as return currents, whether positive or negative.
The positive return current and the negative return current were respectively used to correlate with the positive and negative ion output provided by the static neutralizer, while differences between the positive and negative return currents measured were used to correlate with ion balance. This ion balance was then used to adjust or control ion balance.
But using return currents to determine and control ion balance results in ion current and ion measuring problems if both power supplies energize the same set of emitters through one high voltage bus. As a result, present solutions separately connect the positive power supply to a first set of emitters, named “positive emitters”, and the negative power supply to a second set of emitters, named “negative emitters”, so that the positive emitters do not receive a corona voltage from the negative power supply and the negative emitters do not receive a corona voltage from the positive power supply during operation. Using separate sets of positive and negative emitters, however, leads to another set of problems, such as increasing static neutralizer production complexity, and therefore, cost.
In addition, determining the positive air ion output and the negative air ion output separately requires two current measuring circuits, with one current measuring circuit for each polarity of ion output created. The first current measuring circuit measures the return current between the positive power supply and ground, while the second current measuring circuit measures the return current between the negative power supply and ground.
During a second time period, a negative high voltage power supply 30 provides a negative voltage 32 on emitter array 20 through summing block 22, creating negative air ions 34. Negative high voltage power supply 30 also produces a power supply current 31 that flows from negative high voltage power supply 30, current measuring circuit 14, ground, current measuring circuit 12 and positive high voltage power supply 16. In addition, as negative air ions 34 are generated, electrons flow outward, toward target 36, from emitter array 20, and a negative current 38 results. Negative current 38 flows to ground 26 through current measuring circuit 14. The magnitude of negative current 38 is proportional to the ion current production rate of negative air ions 34 plus power supply current 31.
Positive air ions 24 and negative air ions 34 are mixed and directed, such as by using a directed flow of gas or air, to target 36. Ion balance at target 36 is achieved when the arrival rates of positive air ions 24 and negative air ions 34 are equal. The circuit solution in
Another problem with the solution discussed above includes measurement error and measurement stability. Measuring positive and negative return currents, calculating their differences, and then using the differences to determine ion balance in a static neutralizer is not optimal because these return currents are relatively large when compared to their differences. Since ion balance may be defined to include the difference between a positive return current and a negative current, the return current numbers should be relatively large compared to their difference. The difference between the average positive return current and the average negative return may be nearly zero, but deviations around the average ion balance may be large. Thus, prior solutions that use this approach suffer from balance errors that are determined by the magnitude of the two large numbers rather than the magnitude of the ion balance itself.
A further problem concerns non-representative waveform sampling. In brief, transition currents are averaged into the middle period current. A current waveform (ground to power supply) has a rise period, a low slope middle period, and a fall period. Ignoring the current during the rise and fall periods would be beneficial. A superior measure of air ion production and air ion balance is achieved with only the middle period current.
Another problem involves interaction between the ionizer's feedback adjustment and balance within a target zone. One purpose of feedback technology is to maintain a balance of positive and negative air ions in the target zone. However, some prior art feedback systems operate by changing their respective emitter voltage to adjust ion balance. When emitter voltage is changed, the mobility of air ions is changed because the electric field is different. This causes an ion balance shift at the target.
Consider the case where contamination builds up on a negative emitter. Negative air ion production would decrease. At the ionizer, this would be quantified by a decrease in the negative return current. In response, prior solutions include increasing the corona voltage applied to the negative emitter until the negative return current is restored to a prior determined value.
Increasing the negative voltage at the negative emitter increases the electrical field strength and size that is created between the emitter and the target. A stronger negative electrical field will increase the velocity of negative ions affected by the electrical filed, causing the negative ions to be propelled towards the target at a greater velocity that positive ions. This in turn, will cause ion balance to shift towards a negative bias.
Consequently, there is a need for a control system for static neutralizers that minimizes or avoids some or all of the above described problems.
The present invention pertains to various embodiments for managing ion current balance by independently controlling positive ion current and negative ion current generated during static neutralization. In another embodiment, E-Field compensation may be provided. These embodiments disclose both method and apparatus implementations.
In the following detailed description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments of the present invention. Those of ordinary skill in the art will realize that these various embodiments of the present invention are illustrative only and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having benefit of the disclosure herein.
In addition, for clarity purposes, not all of the routine features of the embodiments described herein are shown or described. It is appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made to achieve the developer's specific goals. These specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine engineering undertaking for those of ordinary skill in the art having the benefit of the herein disclosure.
Positive and negative HVPS 70 and 72 may respectively include control inputs 79a and 79b for receiving control signals, including power-on and power-off signals, from a control system, such as control system 50; control common lines 81a and 81b and voltage output level control inputs 3a and 82b or receiving voltage magnitude control signals through level control input lines 130a and 130b from control system 50. High voltage power supplies that generate high voltages that can be turned-on or off through the power supply control inputs 79a and 79b and that can be adjusted to have a certain voltage magnitude exist and are known, and consequently, are not further disclosed in detail to avoid overcomplicating the herein disclosure.
Current measuring circuit 54 is disposed to measure the current flowing between positive and negative HVPS 70 and 72, emitter(s) 78 and ground 88. Since the current measured represents the flow of current between a HVPS and ground via emitter(s) 78, it is hereinafter referred to as “return current”. As shown in the example disclosed in
Emitters 78 may be housed within an emitter module 76 and are each coupled to an output 71 of summing block 74. In alternative embodiment (not shown), emitters 78 may include two sets of emitters with a first set of emitters disposed to receive the output of positive HVPS 70 and a second set of emitters disposed to receive the output of negative HVPS 72. The emitters in the first set may hereinafter be referred to as “positive emitters”, while the emitters in the second set may hereinafter be referred to as “negative emitters”.
At current measuring circuit output 53, resistor 55 provides a voltage having a magnitude and direction that reflects the magnitude and direction of a current flowing through resistor 55. This relationship is commonly known as Ohm's law, which states that voltage is equal to the product of the current flowing through a resistor, such as resistor 55, and the resistance value of the resistor. It is currently contemplated that resistor 55 has a resistance value that reflects a broad range of current values that can flow between the power supplies during operation, such as a resistance value within the approximate range of 1K to 1 MEG ohms. This resistance range is not intended to limit the present invention in anyway but is provided simply to show one type of current measuring circuit that may be used to measure return current, such as positive return current 98 or negative return current 104, discussed below.
For example and with reference to
The term air ions when used in this disclosure is not intended to be limited to ions formed solely from air molecules but may include ions created in an environment comprised of molecules of a single type of gas or a combination of gases that may or may not include a group of gases commonly referred to as air.
In another example and with reference to
In each of the examples above, current measuring circuit 54 generates a voltage, named feedback voltage, at current measuring circuit output 54. In the current embodiment, this feedback voltage has a magnitude and direction, which may be expressed as voltage polarity, that reflect the magnitude and direction of positive return current 98 or negative return current 104. For example in
As seen in
Rectifier 58 or 60 respectively route feedback voltage 108a or 108b by polarity either to first port 110a or second port 110b. Rectifiers 58 and 60 may be implemented by using precision rectifiers. A precision rectifier generally operates by receiving a signal of either polarity but only permits an output signal to pass through the rectifier of a single polarity. The embodiment shown is not intended to be limited to the use of precision rectifiers, and other types of elements may be used that provide the function of routing the feedback voltage generated by current measuring circuit 54 into first and second ports 110a and 110b according to the polarity of the feedback voltage. For example, in an alternative embodiment, a diode or its equivalent may be used. Diodes and precision rectifiers are known in the art.
Rectifier 58 is disposed to only permit voltage of positive polarity, also referred to as a positive voltage, to reach first port 110a, while rectifier 60 is disposed to only permit a voltage of negative polarity to reach inverter 62. Inverter 62 has an inverter output 111 that generates an output voltage having a magnitude equivalent to the input voltage received but with an opposite polarity. In the embodiment disclosed in
First and second ADC ports 110a and 110b are provided by an analog-to-digital converter, named ADC, 112, which is part of microcontroller 56. Besides ADC 112, microcontroller 56 may further include a microprocessor 114, a digital to analog converter, named DAC, 116, a digital output 118 and a memory 120. Microcontroller 56 may be implemented using model C8051F043, from Silicon Laboratories, Inc. of Austin, Tex. The use of this particular microcontroller is not intended to limit the present invention in any way. Other types of microcontrollers may be used or the configuration shown in
In addition, ADC 112 and DAC 116 are both operated in single-ended mode to obtain the widest resolution possible for their given resolutions. ADC 112 has a digital resolution of 12 bits, which translates to a quantization of 4096 levels when operated in single-ended mode. In an alternative embodiment, if inverter 62 is not used and the output of rectifier 60 is received directly by second port 110b, ADC 112 may be operated in differential mode but will result in half of the available resolution. ADC 112 has an analog resolution range of 0 to 2.40 volts although this resolution range is not intended to be limiting in any way. Any analog resolution range may be used that will accurately measure and capture the full range of feedback voltage that will be received and sampled by microcontroller 56 though ADC 112.
DAC 116 includes DAC output ports 122a and 122b and is capable of converting a digital value, which may be received from microprocessor 114 through a bus 124, into an analog signal. This analog signal may be asserted through at least one DAC 116 output port, such as DAC output port 122a or 122b. The minimum and maximum digital values in which DAC 116 can convert into an analog signal is commonly referred to its digital resolution and in the current embodiment is 12 bits in width, resulting in a digital resolution range of 0 through 4096. In addition, ports 122a and 122b can assert an analog signal within the range of 0 to 2.40 volts, named “analog output signal range,” in a linear proportion to the value of the digital value. Digital to analog controllers are known, and the digital resolution range, analog signal output range and the linearity or non-linearity of the digital to analog conversion taught for the example disclosed herein is not intended to limit the present invention in anyway. Other ranges may be used by those of ordinary skill in the art having the benefit of this disclosure.
In an alternative embodiment (not shown), inverter 62 may be omitted and the output of negative rectifier 60 directly coupled to second port 110b. In this event, one of the 12 bits used by ADC 112 should be used to reflect polarity of the signals received by first and second ports 110a and 110b, reducing the resolution of ADC 112 to half of its available resolution.
Microcontroller 56 through microprocessor 114, which operates through a set of software algorithms that include those described further herein, independently controls the operation of positive HVPS 70 and negative HVPS 72. This set of software algorithms may be stored in a memory (not shown) accessible to microprocessor 114, and includes an ion current correction code 125. The operation of positive and negative HVPS 70 and 72, including controlling power supply power-on and power-off timing, is controlled through signals asserted by DAC output ports 126a and 126b, respectively, from digital output 118. Digital output 118, in turn, receives signals asserted by microprocessor 114 on bus 128, which causes digital output 118 to assert signals on digital output port 126a, 126b or both to control power-on or power-off power supplies 70 and 72.
For example and as shown in
In the embodiment shown in
Besides controlling the operation of positive and negative HVPS 70 and 72, microcontroller 56 also controls the voltage magnitudes of the positive and negative voltage pulses 94 and 100 respectively generated by these power supplies. To facilitate the following discussion, the voltage amplitude of positive voltage pulse 94 generated during at least a portion of first time period T1 is hereinafter referred to as the positive output level. Similarly, the voltage amplitude of negative voltage pulse 100 generated during at least a portion of second time period T2 is hereinafter referred to as the negative output level.
Microcontroller 56 selects these positive and negative output levels by determining the voltage that will be asserted on the respective level control input lines, such as level control input lines 130a and 130b, of positive and negative HVPS 70 and 72. In the embodiments disclosed in
In turn, microprocessor 114 determines the voltage magnitudes that may be asserted by DAC ports 122a and 122b by providing a digital value to DAC 116. Microprocessor 114 selects DAC ports 122a and 122b through address or select lines 132.
Microcontroller 56 uses this digital value presented to DAC 116 to control the positive ion current and negative ion current. Microcontroller 56 selects the actual digital value by, among other things, sampling the feedback voltage received by ADC 112. To control the positive ion current, microcontroller 56 samples the ADC port, such as ADC port 110a, that is disposed to receive a voltage that represents the positive feedback voltage, such as positive feedback voltage 108a in
In a further embodiment of the present invention, microcontroller 56 may include and use program code, which may be herein after also be referred as steady-state sampling code 159 that causes the positive and negative feedback voltages generated by current measuring circuit 54 to be sampled only during the steady-state portion of the feedback voltage waveform, which avoids sampling non-useful rise and fall voltages. For example, as illustrated in
The terms first and second high-slope voltage profiles are intended to include a portion of a feedback voltage, whether positive or negative, in which the magnitude of the feedback voltage for a given time period would not accurately reflect the amount of ion production during emitter cycle 129. The first and second high-slope voltage profiles that respectively occur during the rise-time and fall-time periods are not considered to be an optimum measure of ion output because some of the ion current produced is lost into the system's stray capacitance, causing the return current to not accurately reflect ion current flow. Steady-state period 146 reflects a period during which the return current is a good or accurate measure of air ion production. Consequently, in this alternative embodiment, the sampling period 150a or 150b taken during the first or second time periods T1 or T2 is limited to occur during steady-state period 146a or 146b, respectively.
Based on the return currents measured as described with reference with
Re-establishing positive and negative ion balance may be necessary where at least one emitter point has degraded or become contaminated. Contamination on an emitter reduces positive ion production more than it reduces negative ion production, which reduces or impacts charge neutralization efficiency of a static neutralizer, such as static neutralizer 52 in
Re-establishing ion balance for such a case may require increasing the magnitude of the positive emitter voltage currently used. Increasing the magnitude of a positive emitter voltage may be required, for instance, where at least one emitter in emitter module 76 is degraded or contaminated. However, increasing the voltage received by an emitter may cause a charge plate monitor, such as CPM 80 in
In accordance with yet another embodiment of the present invention, microcontroller 56 may further include program code, which may also be referred to as E-Field compensation code herein, 160 that enables microcontroller 56 to eliminate or compensate for the effect caused on a charge plate monitor by an increase in positive voltage pulse amplitude. E-Field compensation code 160 eliminates or compensates for this effect by changing pulse time duration.
For example and with reference with
If, at a time after the positive voltage pulse is created, microcontroller 56 needs to correct an ion current imbalance during the operation of static neutralizer 52 by increasing amplitude 162 to a higher value, such as amplitude 168, microcontroller 56, operating under E-field compensation code 160, may select a new positive on-time period 170 for amplitude 168 that will result in a positive-pulse waveform area 172 that is equal to the positive-pulse waveform area of the prior used positive voltage pulse, such as positive-pulse waveform area 164 and 94, respectively. In the example shown in
After entering start node 198, two average values are generated 200 that respectively represent the average positive return current value and the average negative return current value that are measured by a current measuring circuit during a selected time period. The current measuring circuit is disposed to measure return current that flows between the positive and negative HVPSs used by static neutralizer 52. For example, as shown in
It is then determined 202 whether ion current correction is enabled, and if so, it is further determined 204 whether a setpoint currently exists. Determining whether ion current correction is enabled may be accomplished by using control system 50, operating under program control, to determine whether a setpoint was previously saved in a memory location (not shown). If so, control system 50 retrieves the setpoint and performs 206 current correction routine that will maintain the positive and negative ion currents generated by static neutralizer 52. Otherwise, control system 50 will acquire 208 a new setpoint, save 210 the new setpoint in memory for subsequent reference and exit through end node 212.
The term “setpoint” is used to collectively refer to a set of values that are used by control system 50 to determine whether the positive and negative ion currents current produced are at a previously established level. Control system 50 also uses these values to maintain ion current if these ion currents are not in balance. These values may include a value representing an average positive return current, named “positive setpoint”, and a value representing an average negative return current value, named “negative setpoint”. The average positive and negative return current values may be generated as described in node 200, above.
In addition, if the method disclosed in
E-FieldSetpoint=(PosHVLevel*PosOnTime)/(NegHVLevel*(TotalOnTime−PosOnTime)) [1]
where E-FieldSetpoint is the new E-Field compensation value; PosHVLevel is the amplitude of the positive voltage pulse generated by a positive HVPS, such as positive HVPS 70; PosOnTime is the period of time positive HVPS 70 is on; NegHVLevel is the amplitude of the negative voltage pulse generated by a negative HVPS, such as negative HVPS 72; and TotalOnTime is the total time that both positive and negative HVPS 70 and 72 are on during an emitter cycle. The PosOnTime and the TotalOnTime values may be used in units of counts, with each count equal to a selected clock cycle.
Determining whether ion current correction is enabled may be performed through the use of a correction flag, which may be set through a user operated switch, the expiration of a pre-selected time period or other selected event,
If at 202, it is determined that ion current correction is not enabled 202, the method ends 212 without ion current correction.
After entering start node 220, negative HVPS 72 is adjusted 222 so that the negative ion current generated by the negative emitter voltage produced during static neutralization remains constant. This may include adjusting the amplitude of the negative emitter voltage so that the negative return current measured by the current measuring circuit, such as current measuring circuit 54 in
Positive HVPS 70 may also be adjusted 224 so that the positive ion current generated by the positive emitter voltage produced during static neutralization remains constant. This may include adjusting the amplitude of the positive emitter voltage so that the positive ion current generated by the positive emitter voltage matches an average positive ion return current that represents the average of a set of positive return currents previously generated. In one embodiment, this average positive return current is in the form of an average positive feedback voltage that was used the positive setpoint calculated in node 208 in
The method in
In accordance with a further embodiment of the present invention and as shown in
The adjustment 222 and 224 of the positive and negative voltage pulse amplitudes used for static neutralization for the method disclosed in
After entering start node 232, a compensation value is generated 234. The calculation of this compensation value may include using a PID (proportional, integration and differential) control algorithm, which is a known in the art of control loop systems. A PID control algorithm includes calculating 236a an error signal, calculating 236b a proportional compensation value, calculating 236c an integration compensation value, calculating 236d a differential compensation value and then summing 236e the proportional, integration and differential compensation values.
Calculating 236a the error signal may include using Equation [2] below:
Err=Setpoint−Calculated Average
where Err is the error signal, Setpoint is the average return current generated by the HVPS saved in 210 and the calculated average is the average return current calculated for the HVPS in 200.
Calculating 236b the proportional compensation value may include using Equation [3] below:
Pcmp=Pgain*Err
where Pcmp is the proportional compensation value, Err is the error signal calculated in Equation [2] and Pgain is a loop gain constant used for the control system, such as control system 50 in
Calculating 236c the integration compensation value may include using Equation [4] below:
Icmp=Ki*ΣErr
where Pcmp is the proportional compensation value, Ki is the integration loop constant used by the control system and Err is the error signal calculated in Equation [2].
Calculating 236d the differential compensation value may include using Equation [5] below:
Dcmp=Kd*(Err−Last Err)
where Icmp is the integration compensation value, Kd is the differential loop constant used by the control system, Err is the error signal and Last Err is the error calculated using Equation [2] from a previous iteration of the method disclosed in
Summing 236e the proportional, integration and differential compensation values may include using Equation [6] below:
Compensation Value=Pcmp+Icmp+Dcmp
where Pcmp is the proportional compensation value calculated in 236b, Tcmp is the integration compensation value calculated in 236c and Dcmp is the differential compensation value calculated in 236d. In an alternative embodiment of the present invention, the compensation value may be calculated using only one or two of the proportional, integration and differential compensation values.
After a compensation value is generated 234, a new control value is generated 238 by adding the compensation value with the control value currently used by control system 50. This control value may be in the form of a 12 bit digital value. The control value is used to adjust 240 the voltage pulse amplitude of the HVPS selected for adjustment. In one embodiment and with reference to
This digital value is checked 242 to determine whether it is outside of the possible range of control of the control system, and if so, a high voltage out of range flag or bit is set and the routine ends 246. If the digital value is not outside of the possible range of control, the high voltage out or range flag or bit is cleared.
After entering start node 252, a new positive on-time period is calculated 254 by using Equation [7] below:
where NewPosOnTime is the new positive on-time period; PosHVLevel is the amplitude of the positive voltage pulse generated by the positive HVPS; E-FieldSetPoint is equal to the E-Field compensation setpoint calculated in Equation [1] above; NegHVLevel is the amplitude of the negative voltage pulse by the negative HVPS; TotalOnTime is the total time (in counts) that both HVPS are on during an emitter cycle
The new positive on-time value is applied 256 to the digital output 118, and it is determined 258 whether the new value is within the range of the control.
If it is found out of the range of control, out-of-range alarm, flag or equivalent is set 260 and the function ends 262. Otherwise, the out-of-range alarm or flag is cleared 264 and the function proceeds to end node 262.
While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments. Rather, the present invention should be construed according to the claims below.
This non-provisional application claims, pursuant to 35 U.S.C. 119(e), the benefit of provisional application 60/790, 424, filed 6 Apr. 2006 and entitled “Control System for Static Neutralizer”.
Number | Date | Country | |
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60790424 | Apr 2006 | US |