GB2115246A

GB2115246A - Overload monitoring

Info

Publication number: GB2115246A
Application number: GB08205058A
Authority: GB
Inventors: Peter Timothy Cogley
Original assignee: BL Technology Ltd
Current assignee: BL Technology Ltd
Priority date: 1982-02-20
Filing date: 1982-02-20
Publication date: 1983-09-01
Also published as: GB2115246B

Abstract

A plurality of electrically powered machines are controlled by measuring the idling power consumption and, periodically, the working power consumption. As long as the difference between these, or a function of the difference, lies within predetermined limits then continued operation is permitted. In the event that the difference, or its function lies outside the predetermined limits then a control signal is generated to modify or stop operation of the machine, or machines, concerned. A control signal is also given if the idling power consumption itself lies outside certain limits. <IMAGE>

Description

SPECIFICATION Power sensor operation This invention relates to a method of controlling the operation of a plurality of electrically powered machines. It is particularly, though not exclusively, applicable to the operation of machine tools such as drills.

It is known to provide electrically powered machine tools with a power monitor that measures the electrical power used by the tool and can be pre-set so that in the eventthe power used exceeds a predetermined value the tool is stopped oran alarm is triggered. The pre-set value is an amount above that required for normal operation with average machining requirements. It has been found that the power consumed infree running (oridling)canalterfora variety of acceptable operating conditions. Thus a responseto absolute power consumption (that isto say idling plus working power) may result in an unnecessary shut down or alarm or, on the other hand, to tool breakage before the machine is shut down.

In our co-pending Application 2074405 there is described a power monitor which takes into account fluctuations in idling power while monitoring machine power consumption while the machine is in operation.

According to the present investigation there is provided a method of controlling operation of a plurality of electrically powered machines each adapted to operate at or between an idling (orfree running) condition and a working condition characterised by (1) Periodically measuring the power consumption (PI) of each machine in an idling condition; (2) determining whetherthevalue of PI iswithin predetermined limits; (3) in the event that the value of Pl is outside a predetermined limit generating an alerting signal;; (4) inthe eventthatthevalue of Pl fora given machine is within the predetermined limits then storing the value of Pl and thereafter measuring the power consumption (PA) ofthe machine in a working condition and relating the value of PAto the stored value of PI forthe machineto provide a powerfunction PC representing power consumption arising from the working condition of the machineoverand above that arising from the idling condition; (5) determiningwhetherthevalueofPCiswithin predetermined limits; (6) in the eventthat the value of PC is outside a predetermined limit generating a control signal to modify or stop operation of the machine concerned.

An exemplary embodiment ofthe invention will now be described with reference to the accompanying drawing of which: Figure lisa block diagram of a control system for a machinetool; Figure 2 is a flowchartofa control programmefor the system disclosed in Figure 1; and Figure 3 is a graphical representation of a metal cutting operation controlled in accordance with the control system of Figure 1.

Figure 1 shows a motor 11 for a drilling machine and fed bya three plase supply line 12. The supply is monitored by means of a transducer 13 which is used to sense the power consumption ofthe motor 11 The outputofthetransducer 13 is fed by line 14to multiplexer15which also receivesalong inputs 16 power indicating signals from other machine tool motors. The output from multiplexer 15 is fed to an analogue-to-digital converter 18 to enable the trans ducer signals to be subjected to digital data processing. This is undertaken by a micro-processor 19 which can be used to process-information in a variety of ways. In addition to inputs from the converter 18 it is also possible to enter data from keyboard 20.

Outputs from the processor 19 are fed to a display system 21 and to a control system 22. The system 22 enables the processor to regulate operation of motor 11 and other devices so as to optimise machining processes, to prevent or limit damage to tools or workpieces orto synchronise operation of a variety of tooling operations.

Figure 2 shows how the control system of Figure 1 is operated in log ic terms. With motor 11 running under no load (idling) condition the system indentifiesthis idling condition and then the output of transducer 13 is scanned by way of processor 19 to ensurethat the idling power consumption Pl lies between predetermined limits. In the event that these limits are exceeded the processor 19 causes a warning or other signal to be transmitted and displayed on unit 21.

lntheeventthatthe value of Pl iswithinthe predetermined limits then the value of Pl is retained until the nexttimethis particularmotor is scanned.

When motor 11 comes on load the output of transducer 13 is again scanned to determine the total power consumption (PA) involved. The processor 19 then determines whether the power required forthe machining operation (PC), which is the difference between PA and PI, lies within predetermined limits.

For as long as the limits are not exceeded the scanning of other transducers is proceeded with cyclically. In the event that the limits are exceeded then the processor causes the control system 22 to modify or stop operation of motor 11. In addition an appropriate signal can be displayed by unit 21.

Figure 3 shows the power consumption for a drilling operation on a crankshaft. The vertical axis represented power consumption and the horizontal axis represents time. The processor 19 is fed the predetermined limits for the values of PI and PC by way of keyboard 20. These values are represented by broken lines 1,11 and Ill for, respectively, low idling speed, high idling speed and maximum power consumption. Trace T represents the actual instan taneous power consumption. Initiallytrace Tshows the horizontal idling powervalue under no load conditions. On starting to drill a progressive increase in power occurs until the maximum working value PA is reached. On completion ofthe operation the drill is withdrawn and the motor reverts to its idling condition.

It will be apparent thatthe various predetermined values can be readily altered. This can be achieved not only by entries on keyboard 20 but also in response to signals representing, for example, changes in type, thickness or material of workpieceor to changes in cutting oil or line speed.

Claims

1. Amethod of controlling operation ofa plurality of electrically powered machines each adapted to operate ator between an idling (orfree running) condition and a working condition characterised by (1) periodically measuring the power consumption (Pl) of each machine in an idling condition; (2) determining whetherthe value of Pl is within predetermined limits; (3) in the eventthat the value of Pl is outside a predetermined limit generating an alerting signal;; (4) in the eventthatthe value of Pl fora given machine is within the predetermined limits then storing the value of Pl and thereafter measuring the power consumption (PA) of the machine in a working condition and relating thevalue of PAto the stored value of Pl forthe machine to provide a power function PC representing power consumption arising from the working condition of the machine over and above that arising from the idling condition; (5) determining whetherthe value of PC is within predetermined limits; (6) in the event that the value of PC is outside a predetermined iimitgenerating a control signal to modify or stop operation of the machine concerned.

2. A method as claimed in Claim 1 wherein the predetermined limits for the value of Pl and/or PC are changed automatically in response to the output of transducers sensing changes in work piece or operating parameters.

3. A method as claimed in any preceding claim wherein the value of Pl is periodically updated so that the stored value represent the most recent periodically measured value of PI.