GB2140937A - Simulation of machine tools - Google Patents

Abstract

A description is given of a method of and a device for detecting whether or not a programmed machining operation on a workpiece by means of a tool will result in a collision between workpiece and tool. To this end, in a simulated machining operation, prior to the actual machining operation, planar projections of the tool 56 and workpiece 60 are displayed as arrays of pixels on a screen 40. Each projected point or pixel corresponding to an elementary volume is indicated as being situated "inside" or "outside" the workpiece to provide additional information about the point. Only during slow drive of the tool in the simulation or in actual maching, is material "removed" by machining, and the added information of a removed point is changed to "outside". When any part of the tool 56 coincides with an "inside" point of the workpiece 60 during the rapid drive in the simulation, a "collision" is signalled. This is also done when any part of the tool coincides with any point of the workpiece fixture 62 during any movement in the simulation. In the case of a signalled collision, reprogramming for actual machining is facilitated by a display of the workpiece on the display screen 40. <IMAGE>

Description

SPECIFICATION Simulation of machine tools The invention relates to a method of simulating the machining of a workpiece by means of at least one tool in order to reduce the workpiece volume by the machining operation, the workpiece, fixture means and tool being displayed on a display screen before as well as during different stages of the simulated machining operation during which the tool follows associated driving paths and the recording of the volume of the workpiece is dynamically updated. A method of this kind is known from the article "Computer verification of machine control data", by L.O. Ward, published in Pioneering in Technology, Proceedings of the 17th NC-Society Annual Meeting and Technical Conference, 27-30 April 1980, Hartford (Conn.), USA, pages 229-320, notably page 303, line 23, to 304, line 45.The use of display screens, for example comprising cathode ray tubes, is attractive, for example because the stimulation does not have irreversible effects. Using a high computing capacity, the known method forms a so-called threedimensional (solid) model of the working situation.

On the one hand, this method offers the operator a very clear view of the occurrences, but on the other hand this method is extremely complex and hence expensive. It is an object of the invention to form an image of the workpiece and its environment using limited means and to indicate, using a limited computing capacity undesirable collisions.This object is achieved in that the invention is characterized in that at the beginning of the simulation operation an image is formed of the workpiece, the tool and the fixture as projected on a two-dimensional sectional plane as a set of pixels having the values of "workpiece point", "fixture point", "tool working point" and "miscellaneous point", respectively, a collision being indicated and the simulation operation being interrupted when, during the following of preprogrammed driving paths by the tool at preprogrammed speeds in a range of values which includes at least one high value (rapid) and at least one low value (cutting), a "tool working point" coincides with any prevailing "workpiece point" at a high current speed of the tool, and also when a "tool working point" coincides with any "fixture point" at any speed of the tool.During simulation, only the tool path need be protected in order to determine the volume reduction of the workpiece as well as to indicate undesirable collisions. Thus, no dynamic access is required to the data which describe the situation at a higher level. In this simple set-up, the image of the workpiece and the tool need not be moved. This simplified result is achieved notably in that first the projection is determined.

The invention can be used mainly, but not exclusively, for chipping operations. Chipping and nonchipping operations can also be performed on one and the same tooling machine by means of different tools/cycles of operations. The different indications per pixel can be realized in various ways, for example by means of mono-colours, mixed colours, a specific shading or pattern assignment, an intensity, for example by assignment of different alphanumerical characters, a time-dependent display with a cycle which is shorter or longer than the response time of the human eye, and soon. The workpiece is usually input as a series of dimensions, so that the projection is given, for example as a polygon. It may alternatively be input as a cycle of sides or corner points.Filling a polygon with coloured pixels is described, for example in the previous British Patent Application 8,405,937 in the name of the present Applicant which Application is incorporated herein by way of reference. The driving paths can be followed at a "low" or feed speed which is intended for the actual machining steps. Furthermore, a "high" speed is customarily used for positioning the tool to and from a working positon. Neither the "low" nor the "high" speed need be restricted to one value only. In the case of a "high" speed, the workpiece may not be contacted. Because the indications are determined in advance per pixel, such contacting can be easily checked. The workpiece volume can be projected on different planes. In the case of a lathe, this will usually be a plane through the axis of rotation.In the case of a milling machine with a face cutting effect, a set of three orthogonal projection planes can be used (in that case one plane is a view from the milling device). In other cases other numbers of projection planes will be used; each projection plane is displayed in its own zone on said display screen. A volume point of the tool may be a "working point" or a "miscellaneous point". A working point is a point which contributes to said volume reduction by direct contact with the workpiece. A working point generally forms part of a straight or curved line of working points. The definition of an "high" current speed is given with respect to a standard speed specifically determined for the relevant tooling machine, machining operation etc. This standard speed may also be dependent on the material of the workpiece.

The fixture means may be a different nature: in the case of a lathe, they are formed by a chuck, support and the like. They are formed by a table in the case of a milling machine. The tool may never contact the fixture. Similarly, volume points of the tool which are not working points may never contact the workpiece at any drive speed. This is usually automatically ensured by the syntaxis of the machining program. For example, in the case of a low drive speed, a drill may be driven only along its axis.

Preferably, an exclusive indication is used for the display of a tool volume. The machining operation is thus better visualized and sometimes reprogramming is facilitated. The indication may be of a different nature, for example a closed contour, an open contour, a separate pixel colour for all volume points.

Preferably, the "workpiece points" are bivalent, that is to say having the values "workpiece point to be removed" and "workpiece point to be saved", respectively, the latter point acting as a "fixture point". This results in a clear visual image and facilitates reprogramming in the case of errors. On the other hand, an already chipped off part of the workpiece may also be given its own indication. Preferably, additional information is also displayed because, for example centre lines, dimensional lines and alphanumerical characters can be superposed on the actual "workpiece/non workpiece" information without the additional information being affected by the volume reduction.

When the invention is used directly on the tooling machine itself, the machining steps of the tool can be checked in advance, so that any accidental damage to the tool or the workpiece or other parts of the machine is avoided, i.e. before the damage is done. Starting can take place by presentation of a new driving path information.

Brief description of the Figures The invention will be described in detail hereinafter with reference to some Figures. First the general procedure will be described, followed by a description of the organization of the display and a device to be used.

Figure 1 diagrammatically shows a lathe; Figure 2 shows an examplary sequence of driving paths; Figure 3 shows a picture in the case of a lathe; - Figure 4 shows a picture in the case of a milling machine; Figure 5 shows the organization of a picture at the information level; Figure 6 shows a block diagram of a device in accordance with the invention; Figure 7 shows an embodiment of the printed circuit board for picture processing; Figures 8a,8b show two flowcharts for the detection of an inadmissible position of the tool.

General procedure A general procedure utilizing a method or a device in accordance with the invention will be described in detail hereinafter on the basis of a lathe. The latter is shown in Figure 1. The reference 20 denotes the chassis or support which comprises several drive mechanisms. Element 22 is the chuck which can be rotated at different speeds by means of a drive spindle. Element 24 is the so-called tailstock which comprises a centring device. Element 26 is the workpiece, which is in this case shown as a cylinder.

The workpiece is clamped in the chuck so that it is rotatable about its axis; it may be centred by the centring device. Element 28 is the saddle which comprises a device for holding one or more tools, such as cutters. The saddle comprises several drive mechanisms for driving the tool in at least the axial and the radial direction with respect to the workpiece under machine control. The saddle can usually rotate about a vertical axis; other possibilities are conventional. Tools can also be clamped in other ways, for example, the centring device may be provided with a drill for forming an axial centred hole. Element 30 contains the numerical control device and comprises a processor, a read write memory, a keyboard, a video display element, further input/output means for the environment, and suitable communication paths between the various parts.Such a lathe can be operated in various ways.

First of all, after the clamping of the workpiece, the instructions can be successively input via the keyboard. For this purpose there is provided, as will be explained in detail hereinafter, a data processing capacity for checking the correct execution of the instructions. Thus, errors are detected which could damage the workpiece, the tool or even the entire tooling machine, because execution ofthe instruction would involve inadmissible positioning ofthe tool. Just before the actual driving step, a check can be made for such errors, a signal is then given if the relevant drive step is inadmissible, so that its execution is blocked. A facility could be incorporated to cancel such blocking by intervention by the operator, the signal "inadmissible" then also being terminated so that the drive step can be executed as yet.The signal "inadmissible" may also be multivalent.

Secondly, the instructions may be continuously stored series-wise in the form of a program in a back-ground memory, for example a punched tape or magnetic disc/tape memory, in order to be fetched after the clamping of the workpiece. The instructions are then executed in the correct sequence, the next instruction being started as soon as the preceding instruction has been completely executed. Any errors can be detected during the execution of the instruction just before the error occurs. The errors can alternatively be detected prior to the start of the actual machining step, for example in that when an actual machining operation or drive step is executed, the next instruction is already fetched from the background memory and verified before it is executed.When the machining program is present in a background memory it is also possible to simulate only the actual operation when the program steps are executed. The actual machining section of the device may then even be absent, so that actually non-local operation takes place. In the latter case the checking of the machining step may commence directly after the preceding step has been checked: it is no longer necessary to await the execution of the driving itself. For the checking of the program as regards syntaxis errors, it is not necessark to perform the simulation; however, it is necessary to do so for the previously described errors which may possibly cause damage.

Figure 2 shows a singular program of driving paths. The first column contains line numbers which do not relate to the execution of the program. The second column contains an identifier of the relevant program step. The third column contains the content of the program step. The fourth column contains a remark. N9000 in the second column identifies the program. The next lines have the identifications N10....which are each time incremented by 10 units.

F100 in the third column indicates the feed speed of the tool in the axial direction. This speed can thus be programmed each time. This is also applicable to other feed speeds, but that is not necessary herein.

The identification GO indicates a fixed and preprogrammed high driving speed of the tool. The indication G1 indicates the feed speed as programmed above. T1 indicates the selection of the tool. S100 indicates the speed of rotation of the chuck to be obtained. M3 indicates that the spindle of the chuck should start to rotate, that is to say counterclockwise (M4 means clockwise, M5 means stop). It is known to equip the lathe with exchangeable tools, for example by means of a turret head. The indications X, Z indicate the radial position and the axial position, respectively. It is assumed that a cylindrical workpiece is clamped with an end face coordinate Z=150. The coordinate of the cylinder surface is X= 150. On line 2 the saddle proceeds to the tool changing position. On line 3 the tool is exchanged.

On line 4 the saddle proceeds to a point just before the first working position: Z distance = 1 higher. On line 5 the diameter is turned off with a radius difference amounting to 1. On line 6 the tool is retracted with an X difference amounting to 2. After the return to line 7 and readjustment of the diameter, on line 9 the diameter is turned off again with a radius difference amounting to 1. It is to be noted that the actual drive mode GO, G1 always prevails until the next drive mode is indicated. The indication M30 signals completion of the program.

Errors occur, for example if the indication Z150 is given on line 7, while on line 8 the drive mode GO prevails and not the indication G1X148. The simulation then signals a collision and an interruption occurs. An other error occurs, for example when an excessive amount of material would be removed, for example when an indication X146 is given on line 8; the actual error signalling then occurs only when the instruction is checked on line 9.

The organization ofthe display Figure 3 shows an example of a pixel-wise display for a lathe. It is assumed that the display means is a television picture tube, but this is not a restriction.

The outline is denoted by the reference 40. Block 54 contains a number of alphanumerical indications which are superposed on the pixel-wise display. At 42/44 the relevant modes are indicated, that is to say the slow drive mode CUT and the rapid drive mode RAP. Different drive speeds are possible per se, and the discrimination between the two modes may also be adjustable. An arrow indicates that the current drive mode is the rapid mode (GO). At reference 46 there is room for the identifier of the current program (so N9000 for Figure 2). At reference 48 there is room for the block or line number (so in Figure 2 the series N10,20...) of the current operation. At the reference 50 there is room for the tool number (so T1 in Figure 2). At the reference 52 there is room for further information, for example concerning the G mode or the M mode.

The remainder of the picture is available for the pixel-wise display of the workpiece. The background ("air") is, for example dark (black). At 56 the complete volume shape of the actual tool is shown.

The shading indicates that it has a first colour. In a simple embodiment, only the "nose" of the tool is indicated, for example by an arrow or other cursor information. Also the complete volume shape of the basic material is shown. The part 60 to be removed has an unique colour. The reference 62 represents the complete volume shape of the fixture (chuck) in as far as it is situated within the outline 40. This fixture has a unique pixel colour. The reference 64 denotes the symmetry axis.

Thus, the various pixel indications are: air, workpiece part to be removed by chipping, workpiece part to be saved, chuck, additional indications, and tool. They can be represented by three bits. In some cases more bits are chosen if the decoding is simplified thereby. When the next movement step of the tool is to the left at a low speed in the picture shown, a cylinder surface is removed. The relevant pixels are then successively addressed and the pixel information is changed into that of "air". (In the case of milling, see Figure 4, there are more possibilitias for the result). When a pixel is addressed in the part 58, an error is indicated and the further simulation or the further drive stops. The same is applicable to a pixel in the part 62.The workpiece shown requires different tools, that is to say at least an outer cutting tool, a drill, an inner cutting tool, and a slottertool for the circular groove. During machining, the additional indications at 50 and also the indication of the symmetry axis may remain uninfluenced. In the organization shown hereinafter, these indications are stored, for example in a separate bit plane.

Before the start of machining, the areas 58, 60 are "inside" the workpiece. The other areas are "outside" the workpiece. At the end of the machining operation, only the area 58 is still "inside" the workpiece. It is possible to use a larger number of different pixel indications, for example for areas which require a finer machining operation such as finish-turning, orforcontours.

Figure 4 shows an example of pixel-wise display for a milling machine. The workpiece is shown in a plan view at 68; it concerns a plate in which various recesses must be formed by means of a face mill. At 70 the front view and the sectional view, respectively of one side is shown, and at 72 those of the other side. These projection conventions are customary.

At 76 the axial representation of the mill is shown, at 78 that which is associated with 72, and at 80 that which is associated with 70. In the position shown, the end face of the mill is situated against the plane containing the upper surface of the workpiece.

Thanks to this display in three projections, every separate motion of the tool can be made visible. The entire picture is enclosed by the boundary 66. The picture is divided into several departments or windows, each of which serves for an associated projection. In the present embodiment, the represen- tation of the tool may be anywhere within the boundary 66. It may be that a window contains only a part of the associated projection of the workpiece.

In that case a corresponding part of the information stored in a memory can also be displayed within this window, it being possible to reposition the window in the memory. Sometimes it is also useful that the scale of display can be changed. One possibility consists in that, depending on the scale factor, the storage in the display memory is updated, starting from a mathematical description of workpiece, fixture and tool. The additional information (area 52 in Figure 3) is not influenced by the window organization.

Figure 5 shows the organization of a picture at the information level. The scale of the picture may be arbitrary. A pixel may correspond to a given space element of the workpiece volume or of the other parts. A picture memory may be suitable for 1024 x 1024 pixels, there being 4 bits per pixel. The addressing is then suitably chosen, for example in that pixels having a successive Z coordinate (Figure 2) also have successive addresses, the last address of a line of pixels being directly succeeded by the first address of the next line. The Figure shows four bit planes, which means that the bits of a pixel are always stored in a corresponding sequence in the bit positions of the associated memory address. The content of the memory location is symbolically shown at "ADDR".The technology of the picture plane memory which is preferably constructed as an integrated solid state memory is not critical. For display in a conventional television format, the numbers of pixels on a horizontal and a vertical cross-section of the picture relate as 4:3.

The information may be organized, for example as follows. Bit plane 0 contains a dynamically adaptable pattern of the material to be removed. When an elementary volume element changes from "material" to "air" due to machining, the information of the associated pixel is updated. Bit plane 1 contains a pixel-wise display of the active pattern (tool),in this case a cutting tool. During movement of this tool, the pattern is updated as follows. The program contains a description of the tool; the information therein indicates: a) a circumscribed figure of the tool, for example a circumscribed rectangle or contour; b) the picture pixels which are to be displaced as "tool pixels", occupying a relative position with respect to a reference position of the tool, for example as a number of vectors.For the initial display, this description is converted into a set of pixels to be displayed as tool pixels. Bit plane 2 contains "protected" information; in this case there are three types of information: a) additional information (Figure 3, area 52) b) contour lines of chuck, material to be retained, orthe area enclosed by these contour lines; c) a centre line, lines of scale and the like.

This information cannot be modified during the execution of the operation/simu lation. The detection of an inadmissible drive position of the tool can be performed in elementary hardware as follows. There is provided a logic circuit which consists of combinatory gates. During the read operation for display, the data bits of a pixel are presented in parallel. A logic "1" indicates a volume point of the relevant category and a logic "0" indicates the absence of such a volume point. In a first AND-gate, the information of the fixture is combined with the information of the tool. In a second logic AND-gate, the information of the workpiece is combined with the information of the tool and with a logic "1" which indicates that a rapid drive mode is executed. The outputs of the two logic AND-gates are combined in a logic OR-gate.

When the latter outputs a "1", an inadmissible drive position has been simulated or realized.

Detailed description ofan embodiment Figure 6 shows a block diagram of an embodiment of a device in accordance with the invention. Element 100 is the actual tooling machine. Connection 102 symbolizes a number of connections for sensors whereby positions of tool and/orworkpiece and drive speeds of tool and/or workpiece are given. In a given realization, these are quantities pulse-shaped signals, each pulse representing a position increment. Accumulation of the position increments results in the position; determination of the number of position increments within a standard period of time is then a measure of the drive speed.Connection 104 symbolizes a number of connections for analog output signals of servo amplifiers and element 106 whereby the tooling machine can be driven in a number of modes of operation; for example, for a lathe: - stop drive spindle, - rotate drive spindle (at different speeds); - axial positive feed (at different speeds); - axial negative feed (at different speeds); - ditto for radial; - rapid axial positive/negative; - ditto radial; - change tool, for example by means of a turret head.

It will be evident that these modes of operation are not all mutually exclusive. For example, the drive spindle may rotate continuously while the other modes of operation succeed one another. Moreover, two rapid drives may take place simultaneously.

During the feed, the drive spindle should continue to rotate in the case of turning. The actual machine 100 furthermore comprises transducers for deriving the driving power signals from a servo control signal in order to deliver power, and transducers which derive pulses from the motions. Bus 108 consists of a number of parallel lines for data, control signals and supply voltages/currents. The element 106 is the interface to the bus 108. This interface comprises D/A converters and fed-check servo amplifiers in order to form an analog control signal for the machine 100 from a digital signal received. Also provided is a device for processing the measuring system data in order to form digital data signals for the bus 108. Two interface units are shown in order to symbolize that these interfaces operate in parallel and can be activated in an arbitrary frequency and sequence.Element 110 is a central processor unit, for example a microprocessor of the type INTEL 8088. This processor locally comprises a peripheral apparatus 112 which comprises an external record carrier, for example a magnetic tape or a punched tape. The actual connection is performed, for example in accordance with the standardized V24 protocol. The central processor unit controls the progress of the machining program or the progress of the simulation of the machining program (the latter possibly in the absence of the elements 100/118).

The central processor unit 110 acts as the master of the bus and applies activation and interrogation signals to the other elements of the circuit. Element 112 is the power supply module. It is connected to the mains connection and provides a power supply current for the other components. Moreover, in the case of an undervoltage condition of the mains, this element can also signal a "not OK" situation, so that all further operations are suspended.

Element 114 is a diagnostic unit. It receives activation signals from the interfaces 106 and also signals from the elements 116,118. During operation, the diagnostic unit verifies that the elements 106, 116 do not output inadmissible combinations of signals. During standstill of the machine, the diagnostic unit can be used for testing, that is to say for simulating and checking the elements coupled thereto. Element 116 is an input/output module for exchanging digital signals directly with the processor. The output signals concern digital control signals for relays and discrete functions of the machine 100 and possibly control signals for the connection of a printer. The input signals from the machine concern different discrete signals such as OK signals.Element 118 is an interface unit between the element 116 and the machine 100 and comprises, for example electromechanical transducers and discrete signalizations.

Element 120 is a connection module for a video unit. It contains inter alia a character memory which can accommodate a number of character codes received via the bus 108, a character generator for converting these codes into character bits in synchronism with the scanning of the picture, and a mixing stage. Thus, for example, program information can be applied to the video monitor 122 which is, for example of a conventional type, via the mixing stage. The video unit 122 is coupled to a keyboard 124; these two units form the actual working station.

The keyboard can be used to issue commands in the same way as the commands given in Figure 2, orto initiate continuation of the machining operation or the simulation of a machining operation after an interruption. Element 126 is the so-called printed circuit board for picture processing which will be described hereinafter. This element is also con necked to an input of said mixing stage, so that the video bits can be output by the connection module.

Description of the printed circuit board for picture processing Figure 7 shows an embodiment of the printed circuit board for picture processing. The central component is formed by the picture processing bus which comprises a data section 132 having a width of 8 bits, an address section 134 having a width of 20 bits, and a control section 136.

Also connected to the picture processing bus are (not shown) a (second) microprocessor of the type INTEL 8088 and a main/program memory. With respect to the central processor unit 110 (Figure 6) this microprocessor acts as a slave processor; it can gain access to the bus 108 only when initiated by the central processor unit. In a simple-set up the memory has a capacity of 64 kbytes of programmable read-only memory (PROM) plus 128 kbytes of random access read-write memory (RAM). By increasing these two capacities, for example doubling, the usability of the system can be enhanced. A bidirectional tri-state communication gate which is connected between the system bus 108 and the picture processing bus 132/134/136 is not shown either. For the meaning of the various lines of the control bus 136 reference is made to the manual of the microprocessor INTEL 8088.The communication gate is capable of interconnecting the picture processing bus and the central bus 108, so that the central processor unit can address the elements connected to the picture processing bus also via the latter bus.

The communication gate can also separate the two buses.

Element 130 is a decoder which is connected to the control section and the address section of the- picture processing bus in order to form a number of selection signals CS for various sub-systems. Element 138 is a control register which is connected to the data section of the picture processing bus in order to store a control work (applied as data) for further elements of the circuit. This register is loaded by an appropriate selection signal from the encoder 130.

Also connected to the data bus of the printed circuit board for picture processing is a g-bit Xaddress register 140 which is filled in two data cycles by way of appropriate selection signals. As is indicated, a first output of this register has a width of 6 bits. Also connected to the data bus of the printed circuit board for picture processing is an 8-bit Y-address register 142 which is filled under the control of an appropriate selection signal. On the printed circuit board for picture processing there is also provided a scanning counter (144) having a 14-bit counting capacity. The outputs of the elements 140, 142, 144 are connected to a multiplexer 146 which comprises 28 bit inputs and 7 bit outputs.

The pixel information is stored in the video memories A (148) and B(150). In the present embodiment the picture is organized so as to have a width of 340 pixels and a height of 256 pixels. There are two bit planes, each of which has a capacity of more than 10 kbytes. Each bit plane is byte-organized, so that each addressing operation produces one byte of output data which concerns 8 successive pixels. The supply of a 14-bit address thus suffices for complete addressing of the video memories. The memory cycle is divided into four parts. During a first part, a first video memory or bit plane is read and a data byte appears on one of the outputs 152/154 in order to be stored in one of the shift registers 160/162.

During a second part of the memory cycle, the same takes place for the second video memory or bit plane and the associated shift register. The data for eight pixels is thus available for display. A third part of the memory cycle is available for the standard refresh operations of these dynamic RAM memories. A fourth part of the memory cycle is reserved for access to the video memories via the picture processing bus. During the line flybackiframe flyback, the actual display is blanked, for example in the element 164 to be described hereinafter.

The following facilities are provided forthe display on the display member 122 in Figure 6. The frequency divider 146 is driven at a clock frequency of 24 MHz from a frequency generator (not shown). Therefrom picture synchronization signals SYNC are derived in order to be applied to the display member 122 for starting the display of a complete picture, starting from an initial position at the top left of a picture The display member operates in accordance with the known television standard with 50 pictures per second, a line period of 64 microseconds, 40 microseconds of which are used for the actual display and 24 microseconds for inter alia the line flyback.

Furthermore, via connections which are not shown, bit synchronization signals are derived from the frequency divider 146, so that the shift registers 160/162 receive a shift pulse for each pixel to be displayed. After the reception of at the most 8 shift puises, they must be filled again by renewed addressing ofthevideo memories 148,150. In this simple embodiment, the series outputs of the shift registers 160, 162 are applied to the logic circuit 164. This circuit is driven (in a manner not shown) by output signals of the control register 138 and possibly by a decoderforthese control signals. Under the control of a first control signal, the logic circuit 164 forms an OR-function of both input signals received.Under the control of a second control signal, the logic circuit 164forms an AND-function of both input signals received. Under the control of a third control signal, the logic circuit 164 forms a correspondence signal for the two input signals received. When the latter signals differ, the correspondence signal has the value "0"; otherwise it has the value "1". The output signal VIDGR is applied to the element 120 in Figure 6. In a preferred embodiment, the data output by the element 164 is modulated so that the impression of a dotted line is obtained by way of small interruptions when horizontal lines are displayed in the picture. For a vertical line, a similar dotted line effect is achieved by the organization according to successive picture lines or scanning lines. However, when complete volumes are to be displayed, this modulation is deactivated.The bit frequency is formed by the display member by dividing the 24 MHz system clock which is also received by the element 146.

In a more elaborate version, the logic circuit 164 can apply one or both input signals received, as desired, to the element 120 of Figure 6. In the latter case the signal VIDGR must have a width of two bits, but the data can then also be displayed in three colours plus black. The range of possibilities can be increased by using more bit planes.

For the processing of the data in the video memories, the output data is selected in the multiplexer 156/158 by the decoding of the three address bits in the X-address register 140 which were not used for the addressing of the video memories 148/150. The output data can be applied to a data buffer 166 in unmodified form, so that it is available on the data bus 132 during a next bus cycle. It is alternatively possible to replace logic circuit 168 by a multiplexerwhich is controlled buy a bit from the control register 138.

Element 170 provides the control of the video memories 148, 150, activated by relevant bits in the control register 138 and by the decoder 130. The video memories 148, 150 are composed of 16-kbit modules of the type INTEL 2118, for which design documentation is published by the manufacturer.

The input data for the memories is derived from the least significant bit of the data bus 132, DGATO. The selection between the two memories is performed, whenever necessary, by a signal (at least three possibilities) in the control register 138: each of the bit plates separately and both bit planes together must be selectable. It is alternatively possible to omit this selection, but in that case the data input for the memories 148/150 should have a width of two bits.

The following control signals are formed in the element 170: RAS: this signal indicates that a signal received from the multiplexer 146 is a row-address signal; this is a conventional signal for this type of memory which is internally formed.

CAS: this signal indicates a column address in the same way.

WR/RE: this signal selects between writing and reading; the operation from the display member 122 always implies a read operation; for the picture processing bus, read operations as well as write operations take place.

CLEAR: this signal erases all data in the video memories 148,150.

INVERT: this signal inverts the relevant bit.

Figures 8a, 8b show two flowcharts for detecting an inadmissible drive position of the tool in a simulation process. Contrary to the hardware solutions suggested with reference to Figure 5 (can also be solved by means of a more elaborate version of the element 164), the further solution can be executed program-wise in the picture microprocessor.

Figure 8a shows the general flowchart for the simulation. In block 200 the instructions and starting parameters of the simulation operation are received.

In block 202 the object to be machined is displayed or pixel-wise stored in the picture memory. In block 204 the same is done for the fixture or for other relevant parts of the tooling machine. In block 206 the same takes place for the tool, starting from a starting position. It is assumed that this starting position is in admissible position. In block 208 the simulation of the displacement of the tool over an elementary distance takes place, said distance corresponding, for example to at the most one bit period in each of the two coordinate directions. In block 210 it is detected whether this is an admissible position. If this is so, it is detected in block 214 whether the process is terminated. For as long as this is not the case, the system returns each time to the block 208. Upon termination of the process, the system proceeds to block 216: stop.When an inadmissible position is detected, the system proceeds to block, 212: wait. Therein, another driving path can be addressed, for example by manual intervention by an operator, or the process can be cancelled. In a test situation it may alternatively be advantageous to document only the inadmissibility, but to continue the process thereafter by an intervention by the operator or even automatically.

Figure 8b shows a flowchart of the procedure in the case of simulation at a lower level. This flowchart is followed each time when the blocks 202 to 208 in Figure 8a are executed. An object is displayed in two steps. During the first step, lines are formed on the image or in the video memory, notably boundary lines. These lines are given by two coordinate pairs or one coordinate pair: a direction and a length. For the execution of the blocks 202,204, each time a closed contour is given as a set of lines (line segments). When all lines are non-interrupted, all enclosed pixels are displayed in the relevant pixel colour. This can be performed, for example in that the pixels of a horizontal line in the picture are successively interrogated.When a pixel which is situated on a line and which has a given colour is encountered, all subsequent pixels obtain the same pixel colour until a next pixel having that colour is found. The subsequent pixels are all displayed in "black" again. In this case "black" is the indication "outside" for the relevant pixel; during the last operation, this indication does not act as a pixel colour: no black lines are formed. In more complex situations, sometimes a more complex algorithm may be required, for example when two parallel lines become coincident due to scale reduction. In this respect reference is also made to the previously mentioned previous British Patent Application in the name of Applicant.

A simplified procedure is followed for the tool: only the relevant contour segments are displayed.

These segments are presented to the data processing elements as a series of pixels, for example with respect to a starting point as (2,4,8, 3, 9). This means: two contour lines depart from the starting point, that is to say one line having a length of four pixels in the direction "8" and one line having a length of three pixels in the direction "9". The directions are numbered in accordance with a com pass card, for example as follows: N=8, NO=9, 0=1 and soon 3,2,6,4,12. In this way (1,4,8,3,9) would indicate a concatenation of two line segments.

Similarly, more complex tool shapes can be displayed.

Block 218 in Figure 8b indicates the start: the instructions and starting parameters are then made available. In block 220 the actual function of the drawing of a line is addressed. In block 222, its subroutine for the display of a pixel is addressed. For the drawing of a line this subroutine must be addressed a number of times. The latter aspect has been omitted for the sake of simplicity. For each pixel the next part of the flowchart is then completed. First of all, in block 224 it is detected whether the pixel to be displayed forms part of the tool. If this is not the case, the relevant pixel is displayed in block 236 and the system proceeds to block 234 (stop or repeat for the next pixel).When a tool pixel is concerned, it is detected in block 236 whether inadmissible coincidence occurs, so between a tool point and a volume point of the workpiece in the case of a high speed, or between a tool point and a volume point of the fixture at any speed. In the case of such coincidence, the system proceeds to block 238 and a waiting situation commences. If said coincidence does not occur, the system proceeds to block 228. Therein, the pixel in the previous tool position which corresponds to the present pixel is erased, the pixel information obtaining the "outside" value, if applicable. Subsequently, the new pixel is displayed as a tool point in the block 230. The system subsequently proceeds to block 234. The operation usually remains very fast, because only a few tool points are involved; in many cases some tens of points already suffice.

In the described embodiment, all tool points are monitored. In some cases this is not necessary and only given points need be monitored, for example, only the apex lines of a drill. The described approach also enables the detection of an excessive force on a tool. For example, in the case of an outside cutting tool the cutting depth may not exceed a given value.

This could be the case, for example, if, a given point of the tool cutting edge were to contact a volume point of the workpiece during an outside cutting operation on a cylinder surface (it is assumed that the drive speed is independent of the radius in that the drive speed of the spindle is readjusted). Another possibility is that the number of points of the cutting edge of the tool which contacts the volume of the tool must be limited. This can be implemented by means of a counter position which is updated for a given line for all relevant points and which is compared with a limit value each time after block 226. A waiting situation occurs again when the limit value is exceeded.

Claims (10)

1. A method of simulating the machining of a workpiece by means of at least one tool in order to reduce the workpiece volume by the machining operation, the workpiece, fixture means and tool being displayed on a display screen before as well as during different stages of the simulated machining operation during which the tool follows associated driving paths and the recording of the volume of the workpiece is dynamically updated, characterized in that at the beginning of the simulation operation an image is formed of the workpiece, the tool and the fixture which is projected on a two-dimensional sectional plane as a set of pixels having the values of "workpiece point", "fixture point", "tool working point" and "miscellaneous point", respectively, a collision being indicated and the simulating operation being interrupted when, during the following of preprogrammed driving paths by the tool at preprogrammed speeds in a range of values which includes at least one high value (rapid) and at least one low value (cutting), a "tool working point" coincides with any prevailing "workpiece point" at a high current speed of the tool, and also when a "tool working point" coincides with any "fixture point" at any speed of the tool.

2. A method as claimed in Claim 1, characterized in that the "workpiece points" are bivalent, that is to say having the values "workpiece point to be removed" and "workpiece point to be saved", respectively, the latter point acting as a "fixture point".

3. A method as claimed in Claim 1 or 2, characterized in that a pseudo-3-dimensional image of the workpiece is formed by way of two images of workpiece, fixture means and tool which are projected on mutually orthogonal sectional planes, and a third image of workpiece and tool which is projected on a plane which is orthogonal to the sectional planes, the indication of collisions in the three planes being performed in a corresponding manner.

4. A method as claimed in any one of the Claims 1, 2 or 3, characterized in that an exclusive indication is used to indicate the tool volume in at least one imaging plane.

5. A device for performing the method claimed in any one of the Claims 1 to 4, characterized in that there is provided a picture memory which has a storage capacity of at least two bits per pixel, and a decoder for decoding the information stored per pixel into a set of at least four different colours.

6. A device as claimed in Claim 5, characterized in that said picture memory comprises a picture plane memory for storing for each pixel additional information which cannot be influenced by the simulation operation.

7. A device for the machining ofaworkpiece by means of at least one tool, comprising a device as claimed in any one the Claims 5 or 6, characterized in that fixture means, drive means and tool holder means are provided, the simulation of the driving of a tool taking place before the driving is performed, the tool drive being deactivated by interruption of the simulation operation.

8. A method of simulating the machining of a workpiece by a machine tool substantially as described with reference to the accompanying drawings.

9. A device for simulating the machining of a workpiece by a machine tool substantially as described with reference to the accompanying drawings.

10. A device for controlling the machining of a workpiece by a machine tool substantially as described with reference to the accompanying drawings.