Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-11-02
2002-06-25
Patel, Ramesh (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S165000, C700S002000, C700S019000, C700S203000, C700S204000, C072S003000, C072S006100, C072S420000, C072S421000, C101S123000, C101S129000
Reexamination Certificate
active
06411863
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to control systems associated with a mechanical press machine, and, more particularly, to an auxiliary control system arranged for use with a programmable logic controller to provide a dedicated, high-performance press controller.
2. Description of the Related Art
Mechanical press machines operate in an industrial environment in which high levels of power transfer are needed over relatively short processing intervals to deliver high impact shaping forces that act through the die assembly to machine an attached workpiece. Machining operations of this type require a control mechanism that monitors the condition of various parts of the press machine and undertakes whatever corrective action is deemed necessary in the event that any abnormal, substandard, or other impermissible conditions arise either in the functioning of the individual devices of the press machine or in the processing activity involving the die assembly and integral workpiece. Some of the critical features for any such control mechanism include near-instantaneous access to and retrieval of monitoring data, rapid processing of the data to arrive at a control decision, and implementation of the decision within a time frame suitable for preserving the press machine against any irreparable harm or other forms of damage materially affecting the integrity of the machine and its operation. This window of protection clearly depends upon the speed of the press, with press running speeds on the order of 400 strokes per minute (spm) necessitating very short intervals of response. The responsiveness to error detection takes on added importance in situations involving press conditions that progressively worsen in the absence of any countermeasures such as when the die members are mispositioned or misaligned, leading to eventual destruction of the workpiece and die assembly that can be averted only if an immediate shutdown is ordered.
The complexity and speed of the tasks that fall to the press controller for their precise and automatic execution suggests a computer-based implementation in order to take advantage of the processing power, data management, and digital control available with microprocessor control apparatus. The complexity of press operation, in particular, usually becomes a vital focus of the engineering effort and typically leads to a press control design based on a general purpose programmable logic controller (PLC). In one representative PLC arrangement, the PLC processor will issue control commands to the clutch control circuit based upon a logic operations analysis of a group of performance measurements obtained from sensors which detect certain performance indicia (e.g., crankshaft angle) representing the operating condition of the press machine. The clutch control circuit directly controls the clutch valves in accordance with its control state as determined by the control commands issued by the PLC. In this manner the PLC can cause the clutch valves to become deactivated, leading to a disengagement of the flywheel and an accompanying stoppage in the slide motion. However, conventional PLC arrangements suffer from a variety of limitations that affect their ability to adequately manage the control activity and meet the real-time demands of high speed machines.
A typical PLC arrangement employs a backplane to serve as the communications bus for interconnecting the PLC processor with the array of individual input/output devices with which the processor interacts in terms of receiving input data for use in executing the control program and transmitting control data for use in controlling the targeted objects. In a machine application, the input devices would encompass the sensors deployed within the press machine and die assembly while the output devices would include the actuators and other control apparatus (e.g., clutch control circuit) arranged to control corresponding machine parts (e.g., clutch assembly). However, for purposes of press machine applications, backplane communications are not sufficiently fast to handle either the transfer of monitoring information from the sensors to the PLC processor or the transmission of logic control data from the PLC processor to the actuator assembly within the time window needed to accomplish real-time processing. Other factors which contribute to the processing delay of the PLC include the clock speed and the execution time of the control program, which increases in a manner commensurate with the size and number of logic operations programmed for execution by the PLC processor.
These features of the conventional PLC arrangement affecting processing speed come together to establish a response window that defines how fast the PLC can analyze the operating condition of the press machine and then implement control decisions in a manner that provides some level of meaningful synchronism between the detection of a press operating event and the controlled response tailored to the detected event. Though possibly adequate at relatively low speeds, conventional PLC arrangements nevertheless become seriously ineffective at higher operating speeds when the machine demands a narrower response window than the PLC can deliver. Consequently, when the response time is too slow, this means that the PLC processor, among other possibilities, is considered to have missed the occurrence of a critical operating event (e.g., a crankshaft malfunction indicated by an out-of-bound crankshaft angle sensor measurement); responded to the operational crisis in an untimely manner that negated any meaningful impact upon press operation; or responded with a control command that no longer harmonizes with the current condition of the machine because of rapid changes in the machine activity that went undetected by the PLC during the intervening processing period. What is therefore needed is a press controller that enables a more rapid coordination and execution of tasks aligned with monitoring the condition of the press machine and implementing the control decisions derived from an evaluation of the monitoring information.
SUMMARY OF THE INVENTION
According to one embodiment of the present invention there is provided an auxiliary control system operatively associated with a press controller which is arranged to control a press machine. The press controller comprises a programmable logic controller including a main processor. The auxiliary control system includes a sensor assembly arranged to provide sensor information which is representative of the condition of the press machine and a die assembly disposed within the press machine. A monitoring device provided in the form of an auxiliary processor is arranged to monitor for the occurrence of press operating events as signified by the sensor information. The auxiliary processor provides a state signal which is representative of the results of the monitoring activity, namely whether one of the press operating events was detected and an indication of which one(s). The press operating events preferably relate to the functioning of the crankshaft from which a measurement of the crankshaft angle is obtained by the sensor assembly. The state signal is provided to the press controller to enable it to take the appropriate control action based upon the state signal.
According to another embodiment of the present invention there is provided a programmable logic controller for use in controlling a press machine. The programmable logic controller includes a main processor and is operatively associated with an actuator assembly arranged to control devices of the press machine in accordance with a control state thereof. The programmable logic controller (PLC) further includes an auxiliary sensor assembly for providing sensor information which is representative of the condition of the press machine and a die assembly disposed within the press machine. An auxiliary logic processor is arranged to perform logic operations in respect of the sensor information and to generate c
Knuth Randall J.
Patel Ramesh
The Minster Machine Company
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