Abstract:
The invention relates to a device for producing and controlling an alternating current with a direct current source in at least one inductive load, in particular for driving a stepper motor, preferably in microsteps.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a device for producing an alternating current with a direct current source in at least one inductive load, in particular for driving a stepper motor, preferably in microsteps, and for controlling a direct current in at least one inductive load.  
         BACKGROUND OF THE INVENTION  
         [0002]    Devices for producing an alternating current with a direct current source are known. An important range of application for such devices is, for example, in digital, particularly electrophotographically operating printing presses. Several stepper motors with different functions can be found in such a printing press. These stepper motors must in part provide vastly different torques for their respective functions, such as a torque of approximately 0.15 N m, or a torque of approximately 3.8 N m, depending on their application. Stepper motors with these types of different torques must be controlled differently. For example, with a control of pulse-width modulation (PWM), a high basic frequency is required for the PWM, since at least one PWM pulse must be produced for each microstep. On the other hand, with high inductances, like those that occur during a high torque, operate against the current, meaning that a low frequency is required when such a motor is operating.  
           [0003]    In principle, there are two different approaches to the driving of stepper motors, each with a special stepper motor with specific functions, i.e., based on either software or hardware. Software solutions are relatively slow and they have a great deal of difficulty complying with the safety requirements in the area concerned. Hardware solutions based on specific IC&#39;s are subject to the prescribed specifications of the manufacturer, so that they are necessarily specified and parameterized for the respective application. Both types of solutions are costly, especially since, as mentioned, even in a single printing press, for example, numerous stepper motors with different special functions can be found.  
         SUMMARY OF THE INVENTION  
         [0004]    The purpose of this invention is to provide devices, which make it possible to take into account the targeted operating conditions of stepper motors in a cost-effective and reliable manner. According to the invention, this purpose is provided by a control loop and an actuator for the control loop, which contain a device for a complex programmable logic (CPLD; complex programmable logic device). This makes it possible, by simply reprogramming the logic, to advantageously provide a flexible adjustment to the control of the load to be operated and to the function of the load without changing the circuit in which the IC is implemented. The invention thus combines the advantages of software and hardware in a certain manner and prevents their disadvantages at the same time. In particular, the logic, once programmed, is as good as a hard-wired hardware and guarantees its operating reliability, but the logic is, on the other hand, simply reprogrammable for other operating conditions.  
           [0005]    The solution according to the invention is also cost effective with respect to its purchase and maintenance. For example, in a single printing press the implemented stepper motors and the associated controls can be substantially standardized. This is readily accomplished by the independent solution of the task at hand, whereby a device according to the invention for controlling a direct current in at least one inductive load is distinguished by a loop and an actuator, which is parameterized or may be parameterized with the application of a (universal) logic description with parametric constants. The logic description can also be universal in the sense that it is essentially standardized and accordingly prepared for the respective function and condition only by feeding the respective parameter constants. Thus the invention already contains a spreading advantage in the parameterization itself, whereby characteristics of the respective special control are concentrated or manifested and reproduced in such parameters.  
           [0006]    The control itself takes place preferably via a pulse-width modulation, as has already been mentioned, particularly for a two-phase control with microsteps. The preferred parameters and parameterizations permit an adaptation of the control to the requirements. As has already been mentioned, low frequencies are required with high inductances, although the pulse-width modulation itself requires a relatively high frequency. The basic frequency of the pulse-width modulation can thus preferably be set according to the invention by a parameter constant especially designated for this purpose, designated in form of an abbreviation as “f_chop_cnt (frequency chopping constant)”.  
           [0007]    When a high precision for the current in the inductance is required, the minimal on-period must be as short as possible. However, the characteristics of high inductances are inconsistent with a short minimal on-period. This minimal on-period can thus also be set preferably by a parameter constant, designated as “Min_on_cnt (Minimal on-period constant)”. The minimal total break period can likewise preferably be set with a parameter constant, designated “Min_off_cnt (Minimal off-period constant)”. The signal traveling time in the feedback path of the loop is not negligible with high frequencies, causing a time lag in the loop, which must be compensated for the operation of the PWM control at high frequencies. Thus, according to the invention, the time lag in the loop and/or the duration of the time lag can preferably and respectively be set via parameter constants, designated as “Comp_dis_del_cnt (Compensation disable delay constant)” and “Comp_dis_len_cnt (Compensation disable length constant)”.  
           [0008]    The device according to the invention controls, as an example, the current in both motor windings of a 2-phase stepper motor. To this end, the necessary output signals for controlling an H-bridge driver are provided, so that either an integrated H-bridge can be used, or for very high currents, a bridge consisting of discreet transistors with the corresponding driver can be used.  
           [0009]    The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Embodiments that also provide further inventive characteristics, to which the scope of the invention is, however, not limited, are shown in the drawings. The following are schematically illustrated:  
         [0011]    [0011]FIG. 1 is a block diagram of a motor-driving circuit for a 2-phase stepper motor;  
         [0012]    [0012]FIG. 2 is an actuator of a motor-driving circuit according to the invention represented in FIG. 1 as a block diagram;  
         [0013]    [0013]FIG. 3 is a device for timing of the actuator represented in FIG. 1 as a block diagram;  
         [0014]    [0014]FIG. 4 is a device for the pulse-width modulation of the actuator represented in FIG. 2 as a block diagram;  
         [0015]    [0015]FIG. 5 is a phase pattern generator of an actuator represented in FIG. 2 as a block diagram; and  
         [0016]    [0016]FIG. 6 is a short-circuit detector of an actuator represented in FIG. 2 as a block diagram. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 shows a block diagram of a motor-driving circuit for a 2-phase stepper motor. The schematically illustrated circuit controls the current of both the motor windings of a 2-phase stepper motor. The motor-driving circuit has an input interface  1 . This is connected with a reference memory  2 , in which the input interface  1  stores addresses and other data, and with a motor control device  3 , which contains in particular the complex programmable logic device according to the invention.  
         [0018]    A motor driver  4  is attached to the motor controlling device  3 . The motor driver  4  contains an H-bridge driver  5 A and  5 B and H-bridges  6 A and  6 B for driving both phase 1 and phase 2 or A and B of a stepper motor. With its output signals, the motor driver  4  controls the stepper motor (which is not shown in greater detail) via an output interface  7 , which emits signals to a power supply device  8  for the stepper motor. For its part, the power supply device  8  is also directly connected with the motor driver  4 . The motor driver  4  is in turn connected via feedback elements  9 A and  9 B and via short circuit branches  10 A and  10 B to the motor controlling device, as a result of which corresponding control loops are formed.  
         [0019]    [0019]FIG. 2 is explanatory with the help of the abbreviations used and words, and the same also applies to the following figures. Consequently, only a few of the illustrated elements are discussed below. Additional conditions can be deduced from the figures. FIG. 2 explains the function of a programmable logic device used as an actuator of a control loop for controlling a 2-phase stepper motor. For this purpose, this actuator contains in particular a timing block  11 , pulse-width modulators (PWM)  12  for the respective phases A and B, phase pattern generators  13  for phase A and B and short-circuit detectors  14  for phases A and B. These blocks  11  through  14  are also represented as block diagrams in the following FIGS. 3 through 6, but with somewhat greater detail of their content.  
         [0020]    The driving signals  23  for the motor windings of the stepper motor are finally provided by the respective phase pattern generator  13 . For this reason, the respective actual phase signal of the phase 1 or 2 and A or B is first input via lines  15  in the respective phase pattern generator  13 . However, modulation signals from the respective pulse-width modulators  12  are also input via lines  16  in the respective phase pattern generator  13 . However, the pulse-width modulators  12  are located in a respective control loop and receive signals from the feedback elements  9 A and  9 B via lines  17 . Furthermore, the pulse-width modulators  12  are also connected to the timing block  11  via lines  24 , which controls them with its time signals and thus the pulse-width modulation decidedly influences and predetermines the respective requirements, conditions and functions of the respective stepper motor.  
         [0021]    It can be deduced from FIG. 2 that the short-circuit loops are available via short-circuit detectors  14  for phase A and B. The short-circuit detectors  14  are linked together by a short-circuit conductor  19 , which are summarized to one line  25  via a junction  26 , and short-circuit detectors  14  are connected together via a line  20 . They are also connected with the timing block  11  via a line  21 . They are arranged via lines  22  on the input side in the short-circuit branches  10 A and  10 B. There are further lines, which can be seen from FIG. 2, i.e., line  27  for a reference-load signal “ref_load”, a line  28  for a signal “load DAC”, a line  29  for a clock signal “clk”, a line  30  for a signal “Comp disable”, explained with FIG. 3, a line  31  for an enabling signal “ena” and a line  32  for a signal “Power on reset”.  
         [0022]    As can be seen in FIG. 3, in which the timing block  11  is illustrated in greater detail, the timing block  11  includes a counter  18  for its time signal, which can be programmed for the respective application according to the invention by the parameter constants input in the timing block  11 , abbreviated as “Min_on”, “Comp_dis_del”, “Comp_dis_len”, “Min_off” and “f_chop”, but being the same constants as mentioned before with their whole names. The counter  18  is directly fed with a clock signal “clk” via the line  29 . A reference-load signal “Ref_load” is conducted in the Counter  18  via the line  27  and via a D-flip flop  33  (the D-input of the D-flip flop  33 ), whereby the clock signal “clk” is transmitted to a clear- or preset-input of the D-flip flop  33  via line  34  and the output-signal of the flip flop  33  is conducted from the output Q via a line  40  to an input of the counter  18 . The output signals of the timing block  11  are the output signals of the Counter  18  and these are a short circuit time signal “shcct_time” on line  21 , the Compensation disable signal “Comp_disable” on line  30 , which compensates the idle time by using the Compensation disable delay constant “Comp_dis_del(-cnt)” and the Compensation disable length constant “Comp_dis_len(-cnt)”, and a chopped clock signal (synchronized) “chop_clk(sync)” on line  24 . The further conducting of these output signals can be seen from and has been explained with FIG. 2.  
         [0023]    The FIGS. 4 through 6 show a pulse-width modulator  12 , a phase model generator  13  and a short-circuit detector  14  in greater detail and they are, as mentioned, self-explanatory for further details, if or as far as not expressively explained in the following. The FIG. 4 shows a pulse-width modulator “PWM”  12  which generates the pulses “PWM — ½” or signals for phases A and B for an input in the Pattern generator Phase A/B  13  via lines  16 . The pulse-width modulators for Phases A and B are substantially the same. They respectively include a RS-flip flop (Set-reset flip flop) in the box  12 . The RS-flip flop receives in its input S via line  24  the “Chop_clk(sync)” signal from the counter  18 , in its clear- or preset-input C via line  29  a clock signal “clk” and in its input R signals “Curr_sens ½” from the feedback elements  9 A and  9 B via lines  17 . The flip flop has an output Q.  
         [0024]    The FIG. 5 shows a Pattern generator Phase A/B  13 , having four NAND-elements  35  with the phase signals “Ph_A/B — 1”, “Ph_A/B — 1*”, “Ph_A/B — 2” and “Ph_A/B — 2*” as their output-signals for controlling the 2-phase stepper motor via lines  23 . The input-signals for the four NAND-elements  35  are the enable signal “Ena” via line  31 , a phase signal via line  15 , the output-signal “PWM” from a pulse-width modulator  12  via line  16 , an over current signal “Over curr” via line  25  and a reset signal “Res” via line  32 , which can also seen from FIG. 2. The FIG. 6 shows a short-cut detector 14 , having an AND-element  36 , a filter  37  and two RS-flip flops  38 ,  39  (with inputs S and R and outputs Q). The output-signal is a “Over_curr — ½”-signal on a line  19 . As input signals the shortcut detector  14  receives a short-cut signal “Shcct ½” via line  22 , enable signals “Ena” via line  31  and a short-cut time signal “Shcct_time” via line  29  (resp. via line  20 ).  
         [0025]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.