Excavating
Patent
1982-07-27
1985-01-08
Atkinson, Charles E.
Excavating
364184, 365228, G11C 2900, G06F 1100
Patent
active
044930836
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method for updating data in bubble cassette memories and, more particularly, to a method for updating data in a bubble memory which enables the simultaneity of data to be preserved even if a power failure should occur in the course of the updating operation.
Wire-cut electric discharge machines are well-known in the art. In such machines a wire is tensioned between an upper guide and a lower guide, and an electric discharge is produced between the wire and a workpiece placed on a table. By moving the workpiece (table) in the X and Y directions along a machining path, the workpiece is cut as instructed. When the wire is tensioned so as to lie perpendicular to the table (workpiece), the upper and lower surfaces of the workpiece can be cut to the same shape. It is also possible to adopt an arrangement in which the upper guide can be displaced in the X and Y directions, such as in a direction at right angles to the direction in which the workpiece is travelling, to incline the wire with respect to the workpiece. This causes the upper and lower surfaces of the workpiece to be cut to different shapes, enabling so-called taper cutting.
A discharge machining operation performed by the wire-cut discharge machine of the aforesaid type can continue for an extremely long period of time, such as 12 hours, 24 hours, and even for as long as one week in some cases. The workpieces which are cut by electric discharge machining generally are mold materials and the like, and some materials can be extremely expensive.
Accordingly, since an interruption in power can occur during machining, such as by inadvertently turning off the power supply or as the result of a power failure due to a lightening bolt or some other cause, it is desired that cutting be resumed, as soon as power is restored, from the position formerly occupied by the wire electrode prior to the power interruption. This prevents the workpiece from being wasted. For a long-term discharge machining operation of one day or one week, as mentioned above, machining proceeds continuously day and night. It follows, then, that there is need for a system which, in the event of a power interruption that occurs at night, is capable of resuming machining automatically without operator intervention after power is restored.
When power is interrupted, there is destruction of information indicative of the current and commanded positions of a motor or of a movable element such as the table, and destruction of positional control information relating to backlash direction, pitch error compensation dog number and the like. There is also complete destruction of the internal status of an NC, which includes interpolation control information such as the number of interpolation pulses produced prior to the power interruption as well as the block number, counting from the beginning of the numerical control data. Also, when power is interrupted, the motor or a movable element such as the table moves by a small amount on the order of several microns, by way of example. Accordingly, when power is cut off during a discharge machining operation in the prior-art arrangement, discharge machining cannot be resumed immediately, in automatic fashion without human intervention, from the position occupied before the interruption in power. Instead, it has been conventional practice to adopt the method based upon the following sequence:
(1) The cutting starting point of the discharge machining operation is stored in memory in advance. For example, this may be set in a digital switch or stored in non-volatile memory.
(2) Following the restoration of power the wire is removed and the table or wire is returned to the zero point of the machine. This brings the position of the table, which is the movable element, or of the wire into coincidence with the current position stored in a volatile memory.
(3) Following the return to the zero point, the table or wire is positioned at the cutting starting point by using the cutting starting point information st
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Heasley, Jr. et al., Error Correction by Reconfiguring, IBM Tech. Discl. Bulletin, vol. 10, No. 10, Mar. 1968, pp. 1543-1544.
Atkinson Charles E.
Fanuc Ltd.
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