Electricity: motive power systems – Positional servo systems – With particular motor control system responsive to the...
Reexamination Certificate
2002-07-29
2004-04-27
Duda, Rina (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular motor control system responsive to the...
C318S696000, C318S599000, C318S811000
Reexamination Certificate
active
06727674
ABSTRACT:
FIELD OF THE INVENTION
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
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.
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'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
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.
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 term “logic description” as used herein, and understood by one of ordinary skill in the art, refers to the description of the implemented logic in a CPLD. A CPLD has a programmable logic that can be described, for example, by a flow chart. In this way, the logic description (description of the implemented logic) is readily apparent. The logic circuit can be parameterized in such a way that it is only necessary to change parameters to chance (customize) the logic circuit. The logic circuit is then like an unchangeable frame which can be filled and customized for respective purposes by choosing appropriate parameter values for the parameters given by the logic. 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.
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)”.
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)”.
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.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.
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Robert J. Heath, et al., “Development, Application, and Verification of a Digital Model of the 3-Phase Current Regulator Function of a Switched Reluctance Cycloconverter Controller”,Proceedings of the 2000 IEEE, pp. 908-913, (Sep. 25-27, 2000).
Schmidt Ulrich
Zessin Jörg
Duda Rina
Kessler Lawrence P.
NexPress Solutions LLC
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