The invention relates to a monitoring system for monitoring processing equipment and in particular, to permit diagnosis of abnormalities in the processing equipment.
Automated production lines are now common for manufacturing a large number of articles where there are a number of repetitive steps which must be carried out on each article during production. Generally, an automated production line has a number of different stations and each station performs a predetermined operation in the manufacture or assembly of the article concerned.
Such automated production lines are now common place in the electronics and automotive industries.
For example, automated production lines are used for the assembly of cathode ray tubes (CRTs) for use in visual display units (VDUs) and televisions. Such a production line takes all the individual components and assembles them to form the finished CRT and then typically subjects the CRT to testing to ensure that the finished CRT operates satisfactorily.
Typically, a CRT production line may assemble a finished CRT from approximately 30 components and the production line may involve in excess of 1000 different steps from the start of the production line to a fully assembled and tested CRT exiting the production line. The total time taken for assembly and testing of a CRT on the production line may be approximately 9 hours.
Therefore, in view of the large number of individual steps which are required during assembly, it can be particularly difficult to determine the location of a fault in the production line rapidly. Rapid location and identification of a fault is desirable in order to minimise the down time in the production line.
In accordance with a first aspect of the present invention, a monitoring system for monitoring processing equipment comprises a controller which emits control signals to control the processing equipment, and a computer coupled to the controller, the computer recording the control signals emitted by the controller and recording status signals from sensors mounted on the processing equipment, the computer representing the processing equipment as a number of individual cyclable units, each cyclable unit having an identical sequence of operations during every cycle, and the computer also recording, for each cycle of every unit, information corresponding to whether the unit has started and completed the cycle.
Preferably, the controller includes a status signal memory which stores the current status signals from the sensors and the computer records the status signals by recording the contents of the status signal memory at regular intervals.
Preferably, the controller includes a control signal memory which stores the current control signals emitted to the processing equipment, and the computer records the control signals by recording the contents of the control signal memory at regular intervals.
Typically, the recording of the contents of the control signal memory by the computer is synchronised with the first control signal emitted by the controller which starts each unit""s cycle.
Preferably, reference data corresponding to a correct cycle of each unit is stored, for example in an electronic database, prior to monitoring the processing equipment. Typically, the data is generated by passing one article through the processing equipment and an operator confirming that each unit has cycled correctly.
Typically, the data stored in the computer comprises the conditions under which each unit starts its operation, and the step in the unit cycle with which the unit starts and finishes.
Preferably, the controller is a programmable controller, such as a programmable logic controller, for example, an Omron Sysmac C1000H programmable controller.
In accordance with a second aspect of the present invention, a method of monitoring processing equipment comprises representing the processing equipment as a number of individual cyclable units, each cyclable unit having an identical sequence of operations during every cycle, and for each cycle of every unit recording whether the unit has started and completed the cycle.
In accordance with a third aspect of the present invention, a method for analysing processing equipment to provide an indication of the location of a fault in the processing equipment, the processing equipment being monitored by a system in accordance with the first aspect, comprises:
(a) determining from the information recorded by the computer which of the units have started but not completed their cycle;
(b) applying the current contents of the status signal memory to the program controlling the programmable controller to derive a set of control signals corresponding to the units which have started but not completed their cycle;
(c) comparing the derived set of control signals with a reference set of control signals to obtain a differential set of control signals, the differential set of control signals being the difference between derived set and the reference set;
(d) comparing the current contents of the status signal memory with a reference set of status signals to obtain a differential set of status signals, the differential set of status signals being the difference between the current contents of the status signal memory and the reference set of status signals; and
(e) comparing the differential set of control signals with the differential set of status signals to obtain an indication of the unit or units of the processing equipment in which a fault may exist.
An advantage of the invention is that by dividing the processing equipment into a number of individual cyclable units, it is possible to accurately predict how each unit is supposed to operate correctly during each cycle as each cycle is identical. This facilitates easier detection of an abnormality in the processing equipment by making it easier to identify the unit in which the abnormality is occurring.
Preferably, the number of units that actually start are compared with the number of units which should start when the production line is operating correctly.
The monitoring system is particularly useful for monitoring processing equipment with independent cyclable operations. That is, that the timing of one cycle is not dependent or related to the timing of a cycle of another unit. An example of such processing equipment is a production line, such as a production line for assembling CRTs.