Abstract:
An ionization system includes a power supply and an ionizer. In a first operating state, properties of an output are set to fixed non-zero baseline levels, and in a second operating state, are set to neutralizing levels. The fixed baseline level is different than the neutralizing level for at least one of the properties. A downstream charge sensor measures an object charge. A controller switches the power supply between the first and second states during a sequence of alternating first and second time periods, during the first time period only, senses a current flow to the ionizer, during the second time period only, receives measured charge data from the sensor, during the second time period only, adjusts the neutralizing levels based on the charge data, and during the first or second time period, calculates an upstream object charge based on sensed current flow or determines a relative ionizer condition.

Description:
BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate generally to an ionization system, and more particularly, to an ionization system with closed loop feedback and interleaved periods of sampling to determine upstream charge on an object and to determine a condition of the ionization system. 
     Air ionization is an effective method of eliminating static charges on target surfaces. Air ionizers generate large quantities of positive and negative ions in the surrounding atmosphere that serve as mobile carriers of charge in the air. As ions flow through the air, they are attracted to oppositely charged particles and surfaces. Neutralization of electrostatically charged surfaces can be rapidly achieved through this process. 
     Air ionization may be performed using electrical ionizers, which generate ions in a process known as corona discharge. Electrical ionizers generate air ions by intensifying an electric field around a sharp point until the field overcomes the dielectric strength of the surrounding air. Negative corona discharge occurs when electrons are flowing from the electrode into the surrounding air. Positive corona discharge occurs as a result of the flow of electrons from the air molecules into the electrode. 
     Ionizer devices, such as an alternating current (AC) or direct current (DC) charge neutralizing system, take many forms, such as ionizing bars, air ionization blowers, air ionization nozzles, and the like, and are utilized to neutralize static electrical charge by emitting positive and negative ions into the workspace or onto the surface of an area. Ionizing bars are typically used in continuous web operations such as paper printing, polymeric sheet material, or plastic bag fabrication. Air ionization blower and nozzles are typically used in workspaces for assembling electronics equipment such as hard disk drives, integrated circuits, and the like, that are sensitive to electrostatic discharge (ESD). 
     In a typical closed loop ionization system for conveyed materials (e.g., webs or the like), sensors are located downstream from the ionizer device. These sensors, typically electrostatic field meters or the like, evaluate residual charge on the material and a feedback signal is returned to the ionization system to drive the residual charge to zero, or as close to zero as possible. In these systems the downstream residual voltage is well characterized by information from the feedback sensor. The actual voltage on the conveyed material coming into the ionization system, i.e., the upstream voltage, is unknown. This information is important for safety and process control. 
     To determine the upstream voltage, an additional sensor located upstream of the ionizer device is necessary. This adds to the expense of the system, but more importantly, the charges on the conveyed material upstream of the ionizer device may be high (e.g., 10 kV or higher) and beyond the capabilities of standard charge sensors. 
     In addition, over time, an ionizer may accumulate debris. In order to maintain optimal performance of the ionizer, it is necessary to clean the ionizer in order to remove the debris. As an ionizer accumulates debris, the ionizer&#39;s charge will decrease and, therefore, the current flowing from the voltage supply into the ionizer will also decrease. A method for having the ionization system self-calibrate and indicate performance is described in U.S. Pat. No. 8,039,789 (Gorczyca, et al.), the entire contents of which are incorporated by reference herein. However, the method requires the initial accumulation of calibration data for a plurality of operating states of the high voltage power supply. Real-time data, in particular a sum of the current output to the positive and negative ionizers, acquired during operation is then compared to the closest data point to determine a difference in performance. The accumulation of calibration data for what may be 250 or more data points can be time consuming, and requires a large memory space to store the necessary baseline table. 
     It is desirable to provide an ionization system that can provide closed loop feedback and estimate upstream charge without the need for an additional upstream sensor. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, an embodiment of the present invention comprises an ionization system for applying or removing charge to a moving object. The system includes a power supply and at least one ionizer coupled to the power supply and receiving an output therefrom. The power supply has a first operating state such that one or more properties of the output are set to fixed non-zero baseline levels, and a second operating state such that the one or more properties of the output are set to neutralizing levels. The fixed baseline level for at least one of the one or more properties of the output is different than the neutralizing level for the at least one of the one or more properties. A charge sensor is arranged downstream of the at least one ionizer and configured to measure a charge on the object. A controller is coupled to an output of the charge sensor and is coupled to the power supply to control the output to the at least one ionizer. The controller is configured to (i) switch the power supply between the first and second states during a sequence of a plurality of alternating first and second time periods, (ii) during the first time period only, sense a current flow to the at least one ionizer with the power supply set to the first operating state, (iii) during the second time period only, set the power supply to the second state and receive measured charge data from the charge sensor, (iv) during the second time period only, adjust at least one of the neutralizing levels for the one or more properties of the output of the power supply in the second operating state based on the measured charge data from the charge sensor, (v) during one of the first and second time periods, perform at least one of a calculation of an upstream charge on the object based in part on the sensed current flow and a determination of a relative condition of the at least one ionizer, and (vi) periodically repeat steps (ii)-(v) for successive pairs of the first and second time periods. 
     A further embodiment of the present invention comprises a method for monitoring the condition of an ionization system for applying or removing charge from a moving object. The ionization system has a power supply configured to provide an output to at least one ionizer, a charge sensor arranged downstream of the at least one ionizer, and a controller coupled to an output of the charge sensor and to the power supply. The power supply has a first operating state such that one or more properties of the output are set to fixed non-zero baseline levels, and a second operating state such that the one or more properties of the output are set to neutralizing levels. The fixed non-zero baseline level for at least one of the one or more properties is different than the neutralizing level for the at least one of the one or more properties. The controller is configured to switch the power supply between the first and second operating states during a sequence of a plurality of alternating first and second time periods. The method includes (a) during the first time period only, sensing a current flow to the at least one ionizer with the power supply set to the first operating state, (b) during the second time period only, setting the power supply to the second state and receiving measured charge data from the charge sensor, (c) during the second time period only, adjusting at least one of the neutralizing levels for the one or more properties of the output of the power supply in the second operating state based on the measured charge data from the charge sensor, (d) during one of the first and second time periods, performing one of a calculation of an upstream charge on the object based in part on the sensed current flow and a determination of a relative condition of the at least one ionizer, and (e) periodically repeating steps (a)-(d) for successive pairs of the first and second time periods. 
     Yet another embodiment of the present invention comprises a method for monitoring the condition of an ionization system for applying or removing charge from a moving object. The ionization system has a power supply configured to provide an output to at least one ionizer, and a controller coupled to the power supply. The power supply has a first operating state such that one or more properties of the output are set to fixed non-zero baseline levels, and a second operating state such that the one or more properties of the output are set to neutralizing levels. The fixed non-zero baseline level for at least one of the one or more properties is different than the neutralizing level for the at least one of the one or more properties. The controller is configured to switch the power supply between the first and second operating states during a sequence of a plurality of alternating first and second time periods. The method includes (a) during the first time period only, sensing a current flow to the at least one ionizer with the power supply set to the first operating state, (b) during the second time period only, setting the power supply to the second state and allowing an operator to change at least one of the neutralizing levels for the one or more properties of the output of the power supply based on charge data measured by a charge sensor located downstream of the at least one ionizer, (c) during one of the first and second time periods, performing one of a calculation of an upstream charge on the object based in part on the sensed current flow and a determination of a relative condition of the at least one ionizer, and (d) periodically repeating steps (a)-(c) for successive pairs of the first and second time periods. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a schematic block diagram of an ionization system in accordance with a preferred embodiment of the present invention; 
         FIG. 2  is a timeline showing alternating and repeating time periods for use in accordance with preferred embodiments of the present invention; 
         FIG. 3  is a flowchart of an exemplary process for closed-loop feedback operation of the ionization system of  FIG. 1  in accordance with preferred embodiments of the present invention; and 
         FIG. 4  is a flowchart of an exemplary process for operation during a sampling period of the ionization system of  FIG. 1  in accordance with preferred embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “a” and “an”, as used in the claims and in the corresponding portions of the specification, mean “at least one.” 
     Referring to  FIG. 1 , a first embodiment of an ionization system  10  is shown. The ionization system  10  includes a controller, processor, or other controlling circuitry  14  or processor  14  (for simplicity, hereinafter referred to as “controller  14 ”) that preferably controls the functionality of the ionization system  10 . The controller  14  may accept input directly from a user  24 , a computer interface  32  coupled to an external computer (not shown), or the like. Various high voltage generating topologies can be used in the preferred embodiments of the present invention. In particular, various controllers  14 , such as microcontrollers or microprocessors, can be used in the application of the preferred embodiments of the present invention. One suitable controller  14  is the commercially available Z8 Encore microprocessor manufactured by Zilog, Inc. The controller  14  is also preferably further in communication with a memory  21 , which can be any known or suitable memory device such as random access memory (RAM), read only memory (ROM), flash RAM, hard disk, optical disk, or the like. 
     The controller  14  is coupled to one or more high voltage (HV) power supplies  22   a ,  22   b , and preferably a positive HV power supply  22   a  and a negative HV power supply  22   b . However, other HV power supplies, such an alternating current (AC) power supply, may also be used in accordance with the invention. The HV power supplies  22   a ,  22   b  supply power, preferably having a voltage in the range of about 3 kilo-Volts (kV) to about 60 kV, to an ionization emitter  16 , shown in  FIG. 1  as an ionizer bar  16 . In a preferred embodiment, the ionizer bar  16  includes one or more ionizing pins  16   a  associated with the positive HV power supply  22   a  and a corresponding number of ionizing pins  16   b  associated with the negative HV power supply  22   b . In other embodiments, one or pins may be alternately connected to positive and negative outputs by switches or the like, or to an AC HV power supply. In embodiments with a single direct current (DC) HV power supply, the ionizing pins of the ionizer bar  16  would receive only one polarity. The controller  14  controls the output of the HV power supplies  22   a ,  22   b  to the ionizer bar  16 . 
     In a preferred embodiment, the controller  14 , the HV power supplies  22   a ,  22   b , and the ionizer bar  16  are disposed within a common housing  18 . This eliminates the need for high voltage cables to connect the ionizer bar  16  to the power supplies  22   a ,  22   b  and provides a more efficiently sized ionization system  10 . However, embodiments of the present invention may be used with other configurations, such as, for example, configurations where the ionizer bar  16  would be located externally from the HV power supplies  22   a ,  22   b  and connected via high voltage power cables (not shown) or the like. 
     The output of the ionizer bar  16  is preferably utilized to apply or remove charge from a moving object  12 , such as a moving web, that is brought within proximity of the ionizer bar  16 . Downstream of the ionizer bar  16  is an external sensor  15  that detects a residual charge on the moving object  12 . During normal operation, data from the sensor  15  is passed into the controller  14 . Based on the sensor data, the controller  14  generates and outputs signals representing adjustments necessary to the output of the HV power supplies  22   a ,  22   b  in order to optimize ionization for the target object  12 , thereby providing closed-loop feedback for the ionization system  10 . In a preferred embodiment an ENABLE signal is provided to the HV power supplies  22   a ,  22   b  to set the timing of the high voltage pulses. Similarly, a V PROG+/− signal is provided to set the respective output levels of the HV power supplies  22   a ,  22   b . These and/or other signals may be adjusted during operation in response to the data received at the controller  14  from the sensor  15 . 
     In another embodiment, the downstream sensor  15  may be a hand-held field meter or a like manual sensor. Charge data collected by the hand-held field meter may be examined by the operator. The operator may be allowed to manually adjust one or more settings of the ionizer (e.g., amplitude, duty cycle, frequency, or the like) to desired levels based on the measured charge data. The operator changes may be made through the user input  24 , the computer interface  32 , or the like. The operator may perform measurements and manual adjustments as frequently or infrequently as necessary. 
     Embodiments of the present invention effectively use the ionizer bar  16  as an “upstream sensor” for determining the upstream charge on the target object  12  (e.g., via the V+/− monitor and/or I+/− monitor signals). When the target object  12  bears a charge of a certain threshold, current flow at the pins  16   a ,  16   b  of the ionizer bar  16  may be induced or suppressed, based on the polarity of the charge on the target object  12 . A difference between an expected current flow and the actual current flow is proportional to the charge on the target object  12 . One method of measuring current flow at the pins  16   a ,  16   b  is described in U.S. Pat. No. 6,130,815 (Pitel et al.) and U.S. Pat. No. 6,259,591 (Pitel et al.), the entire contents of both of which are incorporated by reference herein. 
     For example, the net neutralization current output I neut  at the ionizer pins  16   a ,  16   b  of the ionizer bar can be determined by the following equation:
 
 I   neut   =I   +   −I   −   −I   0  
 
where I +  is the absolute value of the output current at the positive ionizer pins  16   a , I −  is the absolute value of the output current at the negative ionizer pins  16   b , and I −  is a neutralization current present at time t=0, essentially a correction factor, which ideally would be equal to zero. The net neutralization output current I neut  is proportional to charge on the target object  12 , speed of the target object  12 , and distance of the pins  16   a ,  16   b  from the target object  12 . If there is insufficient charge on the target object  12  to induce or suppress current at the ionizer bar  16 , then in most cases the net neutralization output current I neut  would be zero. If I neut &gt;0, then the charge on the target object  12  is negative, but if, on the other hand, I neut &lt;0, then the charge on the target object  12  is positive.
 
     It should be further noted that a normalized net current value I norm  can be used to correct for effects caused by the length of the ionizer bar  114 . The normalized net current is given by the equation:
 
 I   norm   −I   neut   /I   mag  
 
where I mag  represents the magnitude of the neutralization current, which is given by the equation:
 
 I   mag   =I   +   +I   − 
 
     The charge density σ on the target object  12  can be calculated based on the following equation:
 
σ= I   neut /( K·v·W )
 
where v represents the velocity of the target object  12  and W represents the width of the target object  12  covered by the ionizer bar  16  (which is the shorter of the length of the ionizer bar  16  or a width of the object). K represents the neutralizing efficiency, given by the equation:
 
 K= 1−(residual charge/initial charge)
 
which can range in value from 0.1 to 1.1. The actual value depends on the type of ionization emitter  16 , its condition, its installation, distance from the target object  12 , and other variables.
 
     From the charge density a, the electric field strength E can also be determined by the following equation:
 
 E=σ/∈   0   =I   neut /(∈ 0   K·v·W )
 
where ∈ 0  represents the permittivity of free space.
 
     According to embodiments of the present invention, these concepts are utilized by interleaving periods of sampling at the ionizer bar  16  with periods of normal closed-loop feedback operation for neutralizing the target object  12 . For example,  FIG. 2  shows a timeline  100  of operation of the ionization system  10 , which includes alternating periods of normal closed-loop feedback operation  102 , wherein the ionization system  10  is operating under normal conditions to neutralize charge on the target object  12  based on feedback from the downstream sensor  15 , with sampling periods  104 , during which data is collected by the controller  14 , which can be used to determine the upstream charge on the incoming target object  12  and/or to determine a condition of the ionizer bar  16 . It is preferred that the length and frequency of the sampling periods  104  is kept to a minimum, as the ionizing capabilities of the system  10  are may be lessened during the sampling period  104 . It is preferred that a ratio of a length of the normal operating period  102  to a length of the sampling period  104  is about 100:1, although other ratios are contemplated as well. In addition, the ratio may be defined by the operator according to specific operating requirements. For example, the condition of the ionizer bar  16  and the charge on the target object  12  may change relatively slowly, so that the operator can tune the ratio to specific needs. 
       FIG. 3  is a flow chart of an exemplary method  200  performed by the controller  14  in accordance with preferred embodiments of the present invention. During normal closed-loop feedback operation, the controller  14  may check (step  202 ) whether a sampling period should be entered. If not, the controller  14  continues in the closed-loop feedback operation and performs other conventional main loop processes (step  204 ), and adjusts set points if necessary (e.g., amplitude, duty cycle, or the like) (step  206 ) based on input received from the sensor  15  or received from manual operator input (e.g., via user input  24  or computer interface  32 ) based on data measured by the sensor  15  (step  205 ). 
     However, if at step  202  a sampling period is to be entered, the controller  14  may enter the exemplary method  300  shown in  FIG. 4 . Upon entering a sampling period, the power supplies  22   a ,  22   b  are set to baseline levels (step  302 ). For example, typically the output to the ionizer bar  16  is a waveform having a duty cycle, amplitude, frequency, and the like. However, in certain embodiments, the output to the respective ionizing pins  16   a ,  16   b  may be uni-polar DC signals, in which case both the positive and negative HV power supplies  16   a ,  16   b  are constantly on, rather than pulsing. The controller  14  may set the amplitude of the output of the positive and negative HV power supplies  22   a ,  22   b  to a fixed non-zero baseline level, for example between about 4 kV to about 20 kV. The duty cycle (i.e., the ratio of positive to negative ion generation during a cycle of the waveform) is also preferably set to 50/50. The frequency and/or other characteristics of the waveform can also be set to fixed non-zero baseline levels during the sampling period. By maintaining fixed non-zero baseline voltage levels at the ionizing pins  16   a ,  16   b  during the sampling period, the ionization system  10  can continue to apply or remove charge on the target object  12  during the sampling period, with the effectiveness of an open-loop system. 
     In an alternative embodiment, the step of setting the output to baseline levels  302  may include shutting down the voltage output to the ionizer bar  16  from the power supplies  22   a ,  22   b . For example, the power supplies  22   a ,  22   b  may be placed into a mode or set to a set point such that no signal is output to the ionizer bar  16  (e.g., VPROG=0). As a result, the ionizing pins  16   a ,  16   b  are not held at any voltage, and current generated at the pins  16   a ,  16   b  is purely the result of charge on the target object  12 . 
     At step  304 , A/D readings are sampled, such as the current to the ionizing pins  16   a ,  16   b  sensed by the controller  120 . At step  306 , the upstream charge on the target object  12  may be calculated based in part on the sensed current flow, as described above. The calculation in step  306  also preferably takes into account data regarding the target or web  12  speed and/or width (as measured perpendicularly to the downstream direction), as described above. Other like data may also be considered. The speed, width, and other relevant data may be provided by sensors (not shown), although it is preferred that the data is input to the controller  14  via the user input  24  and/or via the computer interface  32 . 
     Data collected at step  304  during the sampling period may also be used to determine the relative condition of the of the ionizer bar  16 . Previously determined calibration data may retrieved from memory  21  for the fixed non-zero baseline levels. An absolute percentage difference is calculated (step  308 ) from the stored value and the real time reading. In a preferred embodiment the calculation used to determine the difference is:
 
 I   D   =[I   cal   −I   mag ]
 
where I D  is the absolute value of base line calibration measurement (I cal ) minus the real-time measurement (I mag ). The retrieved I cal  is assigned a value of 100%. An error from 100% is calculated (step  310 ). The percentage difference E % from the baseline calibration is calculated by the following equation:
 
 E  %=100*(1−( I   D   /I   cal ))
 
Upon calculation of the percentage difference, the meter or display of the ionization system  10  is updated (step  312 ) to indicate operating conditions of the ionizer bar  16 . The percentage difference E % is compared against threshold limits for the ionizer bar selected (step  314 ). A clean bar indicator (not shown) is illuminated when the threshold limit is exceeded (step  316 ). The threshold for the limit wherein the ionizer bar should be cleaned can be configured by the user, a sensor, a microprocessor, or set by software coupled to or located within the controller  120 .
 
     Use of the sampling period also aids in making the self-calibration and performance indication of the ionization system more efficient. The current magnitude I mag  is determined from data acquired by the controller  14  during the sampling period (i.e., in step  304 ). Thus, the calibration set point is preferably identical to the fixed non-zero baseline levels described above (e.g., nominal amplitude and 50/50 duty cycle or the like). By determining the current magnitude based on the fixed non-zero baseline levels during the sampling period, the results can be compared to a single data point, rather than to hundreds of set points encompassing the full operating range of the power supplies  22   a ,  22   b  as programmed by the controller  14 . In addition, such a method would remove the need for obtaining calibration data for hundreds of baseline values at the start of operation. However, it is contemplated that other conventional methods for determining error and operating condition in the ionization system  10  can be used as well. In a preferred embodiment, data collected during the sampling period is used for both determining upstream charge on the target object  12  and determining a condition of the ionizer bar  16 , although the collected data may be used for other purposes as well. 
     Following illumination of the clean bar indicator at step  316 , or if the percentage difference does not exceed the threshold limit, the controller at step  318  preferably resets the power supplies  22   a ,  22   b  to the last closed-loop feedback operating levels in effect prior to entering of the sampling period. At step  320 , the closed loop feedback operation method is re-entered by the controller  14  (i.e., returns to the method  200  in  FIG. 3 ). Upon entry of the next sampling period, the method  300  is repeated. 
     In another embodiment, only the sampling at step  304  occurs during the sampling period. That is, following step  304 , the controller may return directly to step  318  and closed-loop feedback operation. Steps  306 - 316 , wherein the calculations are performed for determining upstream charge on the object  12  and the condition of the ionizer bar  16  may be done during normal operation. In this way, the length of the sampling period may be reduced even further to minimize adverse effects on the application or removal of charge from the object  12 . 
     During the sampling period, data from the downstream sensor  15  may be disregarded by the controller  14 . In other embodiments, communication between the sensor  15  and the controller  14  may be disrupted, or the sensor  15  may be placed into a sleep mode or be shut down (e.g., deactivated) for the duration of the sampling period. Similarly, during a sampling period, the operator may be unable to make any adjustments to the neutralizing levels. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.