Abstract:
A feedback architecture for ionizers that allows simultaneous adjustment of positive and negative ionizer power supplies. Balance and swing data are fed back to the ionizer through an intermediate module, which permits an extra level of signal processing. Swing information is returned to both power supplies in negative feedback mode. If swing is too high, both power supplies lower output. Balance is fed back in both negative and positive feedback mode. This architecture is compatible with multiple sensors and multiple ionizers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/758,434 filed Jan. 11, 2006 entitled “Multiple Sensor Feedback for Controlling Multiple Ionizers”. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not Applicable 
   REFERENCE TO A MICROFICHE APPENDIX 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to ionizers, which are designed to remove or minimize static charge accumulation. Ionizers remove static charge by generating air ions and delivering those air ions to a charged target. 
   One type of ionizer uses corona electrodes to produce air ions. During operation, debris can build up on the corona electrodes and change the ionizer performance. Performance parameters include balance, swing, and discharge time. 
   Sensor feedback to the ionizer is desirable for two reasons. The first reason is maintaining the ionizer&#39;s balance, swing, and discharge time within predetermined limits. The second reason is notifying the user when balance and discharge time breach the predetermined limits. 
   In a conventional closed loop feedback system, one sensor is connected to one ionizer. The one-to-one correspondence is a simple case, and feedback signals can be generated within the sensor itself. 
   The current invention uses novel feedback architecture and signal processing to allow individual or multiple sensors to control individual or multiple ionizers. An intermediate module receives raw signals from one or more sensors, and creates the best feedback instruction. In turn, the best feedback signal is forwarded to one or more ionizers. 
   The position of each sensor is considered when the intermediate module creates the best feedback signal. 
   2. Description Of Related Art 
   Ionizers remove static charge by ionizing air molecules, and delivering those generated air ions to a charged target. The air ions are most commonly created by high voltage applied to corona electrodes. Positive air ions neutralize negative static charges, and negative air ions neutralize positive static charges. 
   From a performance view, ionizers are defined by balance, discharge time, and swing. 
   Balance is a measure of closeness to zero volts. After the initial charge is removed from a target, that target would ideally equilibrate at zero volts from ground. In practice, the target equilibrates near zero volts from ground, but seldom exactly at zero volts. 
   Balance is normally specified as a range around zero. For example, ionizer balance may be specified as −5 volts to +5 volts. If voltages between −5 and +5 volts do not affect products handled within the workstation, the products can be handled safely. But if voltages between −2 and +2 volts affect products handled within the workstation, an ionizer with a tighter balance specification is appropriate. 
   Discharge time is a measure of how fast a given level of charge can be removed from a charged target. Low discharge times are better than high discharge times. For example, an ionizer with a discharge time of 3 seconds could be applied to a moving charged target that only remains under the ionizer for 3 seconds. 
   Swing is the peak-to-peak voltage that an AC or pulsed DC ionizer produces at the target. Static sensitive products can be damaged by high swing, even though the average balance is near zero. 
   Historically, ionizer feedback has consisted of one sensor connected directly to one ionizer. Although this is useful, positional errors are inherent. The single sensor does not represent the ionizer&#39;s performance everywhere within the work zone. Balance may be positive in one location, and negative in a second location. Discharge time and swing also vary with location. 
   A single sensor also reflects grounded objects in the vicinity. For example, a grounded metal object close to a sensor could skew the sensor&#39;s measurements. If the metal object preferentially absorbs positive air ions, the sensor will report a negative balance. In addition, the negative discharge time will increase. 
   Swing is reduced when the metal object reduces the density of both positive and negative air ions. 
   Prior art sensors that are connected directly to an ionizer also miss the opportunity to filter out irregular perturbations. The reason is that the prior art sensors are based on average analog responses, and the perturbation is lost in the averaging. Consider a grounded robot arm that travels between the ionizer and the sensor. When the robot arm is directly under the ionizer, the number of air ions that reach the sensor is reduced. Simultaneously, the balance of air ions may shift. 
   With an intermediate digital module, the opportunity would exist to correct for positional biases, correct for positional variances, and correct for temporal disturbances. Although no prior art systems have pursued this architecture, there is a need. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention incorporates an intermediate module into the ionizer feedback architecture. The intermediate module is positioned between the feedback sensor(s) and the ionizer(s). 
   Sensors provide the information from which feedback signals are generated. But, for this invention, sensors are not connected directly to the ionizers. Instead, the sensors are connected to an intermediate module. Feedback signals are created within the intermediate module. 
   The intermediate module creates several capabilities that are lacking in the prior art. The underlying reason is that the intermediate module introduces an additional level of data processing. 
   In one preferred system configuration, the intermediate module links one sensor to one-or-more ionizers. Linkage means that the sensors within the linked group control the ionizers within the linked group. In a second preferred configuration, two sensors are used. Each of the two sensors is linked with a non-overlapping group of one or more ionizers, and the intermediate module centrally controls two feedback loops. 
   The inventive concept allows linkage among large numbers of sensors and large numbers of ionizers. 
   The inventive concept also allows intentional interaction among linked groups. In this scenario, multiple sensor inputs are combined to create a geographically representative view of the ionizer&#39;s performance within the workspace. When the intermediate module generates its feedback signal, the ionizer&#39;s performance at several locations has been considered. 
   Multiple ionizers can be addressed by the feedback. In one scenario, not all ionizers receive the same feedback signal. Each ionizer is adjusted individually to provide the best overall static charge protection. 
   An intermediate module allows for weighed priorities when generating the feedback signal. For instance, accurate balance directly at a wafer pre-aligner station may be more important than accurate balance close to a side door. If the static sensitive product never gets closer than 12 inches to the side door, the balance condition at the side door has minimal importance. The multiple ionizers can be adjusted to reflect this priority. 
   In an alternate scenario, the goal might be the highest level of uniformity when considering all locations within the workspace. 
   A unique feature of the invented concept involves the category of sensor information upon which feedback is based. Prior art systems create feedback adjustments from balance, discharge time, ion current, and return-current-to-ground. The current invention creates feedback signals from balance and swing (peak-to-peak voltage). Utilizing swing and balance to generate feedback adjustments is a significant departure from the prior art. 
   Other unique features of the invented concept are (1) the direction of feedback for each ionizer power supply, and (2) a requirement for two power supplies in each ionizer (one positive high voltage power supply and one negative high voltage power supply). 
   The directions (positive or negative) of feedback are:
     (1) Swing differences from a swing set-point are negatively fed back to the ionizer&#39;s positive high voltage power supply and to the ionizer&#39;s negative high voltage power supply.   (2) Balance differences from a balance set-point are positively fed back to the ionizer&#39;s negative high voltage power supply.   (3) Balance differences from a balance set-point are negatively fed back to the ionizer&#39;s positive high voltage power supply.   

   Additionally, swing and balance feedback are overlaid, and the updates are made simultaneously. This provides smooth, balanced, and monotonic responses. 
   The intermediate module also provides the opportunity for digital filtering. A short-term perturbation can be recognized and ignored. The result is a more accurate feedback signal that reflects the long-term status of the ionizer. 
   Objects of the invention include (1) providing a feedback architecture that can address multiple sensors and multiple ionizers, (2) providing an intermediate module for generation of feedback signals, (3) providing an additional level of data processing prior to generating a feedback signal, (4) providing weighting factors that reflect ionization priorities, (5) generating feedback signals that vary among ionizers, and ( 6 ) using swing (peak-to-peak voltage) to generate feedback. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a schematic that shows a sensor receiving air ions from one or more ionizers. Balance signals and swing signals and are fed back to two ionizer power supplies through an intermediate module 
       FIG. 2  is a schematic that shows an invented feedback circuit. Information from the sensor is segmented into a balance signal and a swing signal, which are compared to set points. Differences from set points are used to generate feedback to the two ionizer power supplies. 
       FIG. 3  shows prototype data for a step perturbation of both balance and swing. The top line shows positive peak; the middle line shows balance; and the bottom line shows negative peak. A perturbation was applied at time unit  10 . Both swing and balance settled to within 90% of their pre-perturbation values with 40 time adjustment units. 
       FIG. 4  shows the effects of the feedback loop on balance performance as measured on a reference CPM. A perturbation was purposely introduced. 
       FIG. 5  shows higher time resolution of  FIG. 4  after the perturbation. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows one or more ionizers  1  and a sensor  23  operating in a feedback loop through an intermediate module  123 . Two high voltage power supplies  2  (only one is shown in  FIG. 1 ) inside the ionizer place a high voltage on the corona electrodes  3  to produce air ions  4 . 
   A sensor  23  collects the air ions  4  which reach the sensor plate  5 . These air ions  4  contain the information on both balance and swing, but the sensor plate  5  alone does not separate the swing signal from the balance signal. In the embodiment shown, the sensor  23  is combined with the intermediate module  123 , and the balance signal is separated from the swing signal. 
   As shown in  FIG. 2 , the positive HV register  31  and the negative HV register  32  contain the positive HV feedback value and the negative HV feedback value, which are forwarded to the two power supplies  2  within the ionizer  1 . 
   Real-time swing signal  36  is the difference between positive and negative peak measurements for the most recent sampling. Real-time balance signal  45  is the non-alternating component of the total sensor  23  signal. 
   Upon startup, default values are used by the positive HV register  31  and the negative HV register  32  to establish the ionizer&#39;s initial performance. At this time feedback has not been initiated (feedback disabled). During this “feedback disabled” period, the positive input summing block  43  and the negative input summing block  44  do not update the positive HV register  31  and the negative HV register  32 . 
   When feedback is enabled, the real-time swing signal  36  is copied to the swing set-point register  37 . Similarly, the real-time balance signal  45  is copied to the balance set-point register  38 . The swing set-point register  37  and the balance set-point register  38  are not updated again until the feedback is disabled, then subsequently re-enabled. 
   When feedback is enabled, the difference between the swing set-point register  37  and the real-time swing signal  36  is zero, as calculated by the swing summing block  39 . Similarly, the difference between the balance set-point register  38  and the real-time balance signal  45  is zero, as calculated by the balance summing block  40 . 
   Additionally, at the time that feedback is enabled, the zero balances at the swing summing block  39  and the balance summing block  40 , propagate through the remainder of the circuit to the positive HV register  31  and the negative HV register  32 . Zero contribution is added to both the positive HV register  31  and the negative HV register  32 . 
   At a later time, when dirty or worn corona electrodes in an ionizer  1  change the ionizer&#39;s  1  performance, the real-time swing signal  36  will differ from the swing set-point register  37 , and the value of the swing summing block  39  will be non-zero. Similarly, the real-time balance signal  45  will differ from the balance set-point register  38 , and the value of the balance summing block  40  will be non-zero. 
   The value from the balance summing block  40  goes through a balance gain stage  42 , which controls the speed of the response to a change in balance. The output of the balance gain stage  42  integrated into the next update of the positive HV register  31  and the negative HV register  32 . In one preferred embodiment, the balance gain stage  42  is set to 0.00025 for a particular ion sensor. This produced the responses shown in  FIGS. 4 and 5 . 
   The output from the balance gain stage  42  is propagated through positive input summing block  43  and through negative input summing block  44 . The output from the balance gain stage  42  is negatively applied to the positive input summing block  43  and is positively applied to the negative input summing block  44 . Therefore, if the balance drops negatively, the output from the balance gain stage  42  will go negative, which will increase the subsequent value of positive HV register  31  and reduce the subsequent value of negative HV register  32 . 
   As positive HV register  31  is increased and the negative HV register  32  is decreased, the real-time balance signal  45  will subsequently change in the positive direction, and the output of the balance summing block  40  will decrease exponentially toward zero. This will reduce future adjustments to the positive HV register  31  and to the negative HV register  32 , tending toward zero. 
   Similarly, changes in the real-time swing signal  36  generate non-zero values from the swing gain stage  41 . But conversely to the balance, the swing gain stage  41  will be subtracted from both the positive HV register  31  and the negative HV register  32 . For example, if the real-time swing signal  36  drops, the output of the swing gain stage  41  will go negative, and both the positive HV register  31  and the negative HV register  32  will increase. In turn, real-time swing signal  36  will return to the level in the swing set-point register  37 . 
   In summary, the new HV levels are represented by the following formulae, calculated at each update period.
 
 HV Level+ HV Level+−GainSwing(Swing−SwingSetpoint)−GainBalance(Balance−BalanceSetpoint)
 
 HV Level−= HV Level−−GainSwing(Swing−SwingSetpoint)+GainBalance(Balance−BalanceSetpoint)
 
     FIG. 4  shows the effects of the feedback loop on balance performance as measured on a reference CPM. The imbalance perturbation was introduced by grounding a piece of copper tape near one of the negative corona electrodes. After dozens of minutes, the feedback loop compensates for the perturbation, and returns the balance to initial levels. 
     FIG. 5  shows higher time resolution of  FIG. 4  after the perturbation. The feedback loop compensated for an extraordinarily large artificial imbalance.