GB1568707A - Data processing equipment - Google Patents
Data processing equipment Download PDFInfo
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- GB1568707A GB1568707A GB2253576A GB2253576A GB1568707A GB 1568707 A GB1568707 A GB 1568707A GB 2253576 A GB2253576 A GB 2253576A GB 2253576 A GB2253576 A GB 2253576A GB 1568707 A GB1568707 A GB 1568707A
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B19/00—Programme-control systems
- G05B19/02—Programme-control systems electric
- G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
- G05B19/416—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control of velocity, acceleration or deceleration
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- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Numerical Control (AREA)
Description
(54) DATA PROCESSING EQUIPMENT
(71) We, NATIONAL RESEARCH
DEVELOPMENT CORPORATION, a
Body Corporate established by Statute, of
Kingsgate House, 66/74 Victoria Street,
London SWIPE 6SL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to numerical control systems.
In many types of numerical control systems for automatic machinery (such as automatic lathes, milling machines or plotting equipment) data processing equipment is used to generate control commands for operating the machinery so that continuous contours formed by straight lines and circles are followed. In known data processing equipment sequential output control command signals are provided by an interpolator to servo drive members of the automatic machinery, these output signals being continuously calculated from input information representative of the end point of the preceding step and the beginning and end points of the contour.
For example, in the case of a contour which is in the form of a circle each output control command signal has been arranged to provide a linear movement of the machinery corresponding to a chord of the circle such that the sagittal error between the generated path and the true curve is within predetermined limits. The interpolator operates on an iterative basis at a rate determined by the control commands. This iteration rate is dependent upon the maximum time interval (try) which can be permitted between iterations if the sagittal error is to be constrained, and if the servo drive members are to operate without introduction of errors, and if the centripetal acceleration of the machinery is to be constrained, and if the operating tool of the machinery is to operate efficiently.In the known systems where trn has been calculated a fairly powerful computing section has been required to cope with the complexity of the calculations to be undertaken or updated by the interpolator in the time allowed for iteration.
It is an object of the present invention to provide a simplified form of numerical control system wherein the complexity of these interpolation calculations can be reduced and the frequency of evaluation reduced whereby less powerful computing facilities can be used.
According to the present invention there is provided a numerical control system for automatic machinery wherein sequential control command signals are output from an interpolator, including data processing equipment for determining the rate at which said control command signals are calculated and generated, said data processing equipment comprising a shift register, means for entering data representative of the feedrate of the machinery into the shift register, a comparator, means for applying the data in the shift register to one input of the comparator, means for applying data representative of the permitted maximum time interval (tm) between control command signals to the other input of the comparator, means for repeatedly effecting a shift of the data in the shift register until such time as the output of the comparator changes state, and means responsive to said change of state for transferring the data in the shift register to said interpolator as a measure of the time interval (t,) between control command signals.
Further according to the present invention there is provided a numerical control system for automatic machinery wherein sequential control command signals are output from an interpolator, including data processing equipment for determining the rate at which said control command signals are calculated and generated, said data processing equipment comprising::
a shift register for initially holding data representing the machinery feedrate,
first, second and third comparators,
means for applying data representative of the permitted maximum time interval (try) between control commands to a first input of the first comparator,
means for applying to a first input of the second comparator data proportional in value by a factor K1 to the data applied to the first input of the first comparator, where 1#K1-1#2, means for applying to a first input of the third comparator data proportional in value by a factor K2 to the data applied to the first input of the first comparator where K1 'AK-2'A2, means for applying the data in the shift register to the second input of the first comparator,
means repeatedly effecting a shift of the data in the shift register until such time as the output of the first comparator changes state,
means responsive to the change of state of the first comparator for applying the data in the shift register to the second input of the second comparator,
means responsive to the change of state of the second comparator for applying the data in the shift register to the interpolator,
means responsive to the change of state of the first comparator for applying the data in the shift register to the second input of the third comparator,
means responsive to a change of state of the third comparator to apply to the interpolator the data in the shift register decreased by said factor K1, and
means coupled to the output of the third comparator to apply to the interpolator the data in the shift register decreased by said factor K2, in the absence of a change of state of the third comparator.
The terms "shift register" and "comparator" as used herein are intended to embrace any form of equipment capable of undertaking the known functions of data storage, data shift and data comparison and for example may be implemented by such stored programme devices as a mini computer or a micro processor. Left shift of data by n places is equivalent to multiplication of the data by 2n whereas right shifting by n places is equivalent to dividing the data by 2".
First and second embodiments of the present invention will now be described by way of example with reference to block diagrams respectively denoted Fig. 1 and
Fig. 2 in the accompanying drawing.
In Fig. 1 there is shown a numerical control system 10 for controlling an automatic machine 12 by means of sequential control demand signals output from an interpolator 14 at a rate determined by data processing equipment 16. The equipment 16 comprises a shift register 18, a shift control 20, a comparator 22, a monitor 24 connected to monitor the output of the comparator 22 and inhibit further operation of the shift control 20, and a gate 26 connected between the output of the register 18 and the interpolator 14, the gate 26 being opened by the monitor 24. The register 18 is fed with data representative of the feedrate of the machine 12 from an input device 28 and the comparator 22 is fed from an input device 30 with data representative of the maximum time interval tm permitted between control command signals at the output of the interpolator 14.The interpolator 14 is fed with input data concerning the contour to be followed by an input device 32.
The operation of the system 10 will be explained with reference to examples 1--3 hereinafter.
In Fig. 2 the numerical control system is 50, the machine is 52, the interpolator is 54 and the data processing equipment is 56.
Equipment 56 comprises a shift register 58 with shift control 60, and first, second and third comparators 62, 64, 66. Register 58 is connected to an input of comparator 62 and via gates 68, 70 to comparators 64, 66 respectively. Gates 68, 70 and shift control 60 are controlled by a monitor 72 at the output of comparator 62. Comparator 62 is fed from an input device 74 with data representative of the maximum time interval tm permitted between control command signals at the output of the interpolator 54; comparator 64 is fed from device 74 via a multiplier device 76 which applies a factor K1 and comparator 66 is fed from the device 74 via a multiplier device 78 which applies a factor K2.Alternatively since trn, K1 and K2 are known the evaluation of K1tm etc. may be undertaken externally of the equipment 56 and fed directly to the comparators 64, 66.
The register 58 feeds into the interpolator 54 through three gates 80, 82, 84. Gate 80 is operated by a monitor 86 at the output of comparator 64, and feeds the register data directly into the interpolator; gate 82 is operated by a first monitor 88 at the output of comparator 66 and feeds the register data to the interpolator through a device 90 which decreases the data by the factor K,; and gate 84 is operated by a second monitor 92 at the output of comparator 66 and feeds the register data to the interpolator through a device 94 which decreases the data by a factor K2. The register 58 is fed with input information from a device 96 and the interpolator is fed with input information from an input device 98.
The operation of the system 56 is explained with reference to Example 4 hereinafter.
EXAMPLE 1
In the case where a contour is to be generated from position (x0 y0) to position (x1 y,) following a circle which has its centre at position (ij) and moving at an optimum feedrate of a, rads/sec., an incremental angle a (radians) is selected of magnitude 2-" where n is a positive integer.It follows that the time interval t1 for each step is given by tl=###-1
=2-n##-1 because t, < tm the maximum iteration time interval (which is a known value) the parameter n can be evaluated from the relationship tm#tl
##-1#2-n or alternatively t-1m###2n If # is entered into a shift register and tm1 is applied to one input of a comparator the other input of which is taken from the shift register it follows that simply by repeatedly left shifting the data in the register the output of the comparator will change state when n is of sufficient magnitude.It will then follow that tm-1###2n#2#tm-1 which can be re-written as tm#tl#2-1#tm Thus, in response to the comparator changing state the data in the shift register (viz###2n=tl-1) is transferred to the interpolator to initiate calculation of the control command signals and to determine the rate of generation of control command signals.
It will be noted at this stage that by virtue of the selection of #=2-n radians the interval between control command signals t, can be evaluated without recourse to accurate and complex multiplication and division facilities. Additionally however, by virtue of this identity the evaluation of interpolation calculations is greatly simplified. This can be explained by considering the interpolation outputs required to move from a position (xR yR) along a circle centred at the origin and of radius R.
In polar co-ordinates (xR YR)=(R COS 0, R sin 0) where 0 is the angle between the line from the centre of the circle to the position (xR yR) and the abscissa of the co-ordinate axes, then for an angular shift of a it follows that the co-ordinates (x, y) of the new position are given by
x=R cos Ú cos #-R sin 0 sin a xR#cos #-yR#sin # and
y=R cos o sin a+R sin o cos a
=XR sin #+yR cos a now because a is very small the exponential expansion for the circular functions can be reduced to, say, one term, whereby,
sin a=.a and
cos #=1 In consequence
x becomes xR-#yR and
y becomes yR+#xR and because a=2-n x becomes xR-2-n
y becomes yR+2-n and both x and y can be evaluated without multiplication or division since 2-n#yR can be evaluated by entering yR into a shift register and shifting the entered data n places to the right.
If a greater degree of accuracy is required in evaluating x and y the exponential expansion can be increased to two terms, so that #3 sin a6.a+ 13 cos=1-#2#2-1 it then follows that x becomes xR-xR#2-2n#2-1-yR#2-n+yR#2-3n#6-1 and by using the approximation
1/6=2-3+2-5+2-7 it follows that x reduces to @#2-2n-1-yR#2-n+yR
+yR#2-3n-5+yR#2-3n which can be evaluated using right shift registers.
Similarly y reduces to an expression y=xR#2-n+xR#2-3n-3+xR#2-3
+xR#2-3n-7+yR-yR#2-2n-1 which can be evaluated using right shift registers.
If still greater accuracy is required more than two terms of the exponential series may be used in a similar manner.
It will now be appreciated that by virtue of the selection of #=2-n the requirements for computing the interpolation signals are greatly simplified to shift registers and addition and subtraction counters and the calculations are only performed at intervals of tl secs. which allows implementation by a micro processor with a minimum of external hardware.
EXAMPLE 2
In the case where a contour is to be generated from position (x0 y0) to position (x, y,) along a straight line at an optimum feed rate V, 2-" number of steps is selected where n is a positive integer.
It follows that if D is the distance between (x0 y0) and (x, y,) each step is of length
D #2-n; and at a feedrate of V the step time interval t, is given by
tl=D#2-n#V-1
Because t,6tm the maximum iteration time interval (which is a known value) the parameter n can be evaluated from the relationship
tm#tl
#D#V-1#2-n or alternatively tm-1#V#D-1#2 This evaluation is achieved in the manner set forth in Example 1 since the equations to be solved are analogous.
Also, as in the case of Example 1, the evaluation of interpolation calculations is simplified by the selection of 2-" steps. This can be explained by considering the incremental movement ax and ay required to move from position (x0 y0) to a position (x.y). Since the contour extends from (x0y0) to (x1y1) #x=x1-x0
#y=y1-y0 and because there are 2" steps each step is of length #x#2-n in the x-direction and #y in the y direction.Thus #x=#x
#y=#y and this can be evaluated by entering ax and ay in shift registers and shifting the entered data n places to-the right
EXAMPLE 3
In examples 1 and 2 an equation in the form tm-1#K#2n has been derived and solved by entering the data K in a shift register and thereafter successively left shifting the data n times.
However the reciprocal of this equation may be solved by entering the data K-' in a shift register and successively shifting the data to the right n times to satisfy the equation tm#K-1 Thereafter the interpolation calculations are carried out as previously described in
Example 1 or Example 2 according to whether the contour is curved or linear.
EXAMPLE 4
In the foregoing examples the equation to be solved is in the form tm-1#K#2n and gives rise to the relationship 2-1#tm#tl#tm which can be wasteful of processing power.
Therefore in this example the equation to be solved is put in the form tm'6K 2 where p is either 0 or 1 and 2-r evaluates to be a simple fraction the denominator of which is an integral power of 2, such as 3/2 or 5/4 or 7/4.
Evaluation of this modified equation is now carried out in two stages, firstly with p=O when the register shift procedure previously explained is undertaken. On reaching the conclusion of this stage, i.e.
having evaluated tm#tl#2-t#tm the data in the shift register is compared against 2Pr . tm-1 with p=1.
If K.2n#2pr.tm-1 then in Example 1 the value of #=2-n is used and in Example 2 the value of ôx=åx- 2-n is used. If however K#2n#2pr#tm-1 when 2-r=5/4 then the procedure can be repeated when 2-r=3/2.Thus if
K 2n > 2Pr- tm1 the values of ô and ax used in
Examples 1 and 2 are respectively modified to #=5/4#2-n
#x=5/4##x#2-n If however K#2n < 2pr#tm-1 with 2-r=3/2 then the values of # and #x in examples 1 and 2 are respectively modified to ô=3/2 2 n
#x=3/2##x It will be noted that because 2-r evaluates as a simple fraction and tm is a known constant quantity for any particular set of circumstances the quantity 2r#tm-1 can be evaluated quite simply. However, having modified both a and ax the evaluation of the interpolation calculations becomes more complex as will be demonstrated.
Consider the circular contour case of
Example 1 with Ô=2-n .2-r and expanding the circular functions to two places, thus,
sin a=2- . 2-r2-3n . 2-3r. 6-1 and
cos a=l-2-2 . 2-2r. 2-1 and in the specific case of 2-r=3/2
3 27 1
sin #=2-n#--2-3n#-#- 2 8 6
1 1 1
=2-n(1±)-2-3n(-±)
2 2 16 =2-n+2-n#2-1-2-3n#2-1-2-3n#2-4 and similarly cos # may be evaluated in powers of 2 whereby the evaluation of x and y can be achieved by shift registers as previously described.
A system for implementing this procedure is illustrated in Fig. 2.
In the event that it is desired still further to conserve processing power the three single fractions, namely 3/2, 5/4, 7/4 may be used in a modification of the Fig. 2 system wherein a fourth comparator is provided with attendant components in a manner similar to the second and third comparators.
It will now be appreciated that the forgoing examples provide for an evaluation of the parameter 2n from time to time along the length of a given contour.
Thus for example where a contour changes from linear to curved or changes centre or radius of curvature with which there is associated a new value of feedrate parameter there is a re-evaluation of 2".
Similarly where there is a requirement to effect a feedrate change within a given contour such as towards the ends of the contour the attendant acceleration or deceleration can be achieved by reevaluation of 2". Thus the time at which interpolation steps are taken is variable. The size of the interpolation steps may also be made variable to allow for acceleration and deceleration by introduction of a factor K where K+l in evaluation of 2", i.e. K. 2" is evaluated.
WHAT WE CLAIM IS:
1. A numerical control system for automatic machinery wherein sequential control command signals are output from an interpolator, including data processing equipment for determining the rate at which said control command signals are calculated and generated, said data processing equipment comprising a shift register, means for entering data representative of feedrate of the machinery into the shift register, a comparator, means for applying the data in the shift register to one input of the comparator, means for applying data representative of the permitted maximum time interval (try) between control command signals to the other input of the comparator, means for repeatedly effecting a shift of the data in the shift register until such time as the output of the comparator changes state, and means responsive to said change of state for transferring the data in the shift register to said interpolator as a measure of the time interval (t,) between control command signals.
2. A numerical control system as claimed in Claim 1, wherein the shift register is controlled to left shift, and the data applied to the other input of the comparator is the inverse of the permitted maximum time interval (tm).
3. A numerical control system as claimed in Claim 1, wherein the shift register is controlled to right shift, the data initially
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (6)
1 1 1
=2-n(1±)-2-3n(-±)
2 2 16 =2-n+2-n#2-1-2-3n#2-1-2-3n#2-4 and similarly cos # may be evaluated in powers of 2 whereby the evaluation of x and y can be achieved by shift registers as previously described.
A system for implementing this procedure is illustrated in Fig. 2.
In the event that it is desired still further to conserve processing power the three single fractions, namely 3/2, 5/4, 7/4 may be used in a modification of the Fig. 2 system wherein a fourth comparator is provided with attendant components in a manner similar to the second and third comparators.
It will now be appreciated that the forgoing examples provide for an evaluation of the parameter 2n from time to time along the length of a given contour.
Thus for example where a contour changes from linear to curved or changes centre or radius of curvature with which there is associated a new value of feedrate parameter there is a re-evaluation of 2".
Similarly where there is a requirement to effect a feedrate change within a given contour such as towards the ends of the contour the attendant acceleration or deceleration can be achieved by reevaluation of 2". Thus the time at which interpolation steps are taken is variable. The size of the interpolation steps may also be made variable to allow for acceleration and deceleration by introduction of a factor K where K+l in evaluation of 2", i.e. K. 2" is evaluated.
WHAT WE CLAIM IS:
1. A numerical control system for automatic machinery wherein sequential control command signals are output from an interpolator, including data processing equipment for determining the rate at which said control command signals are calculated and generated, said data processing equipment comprising a shift register, means for entering data representative of feedrate of the machinery into the shift register, a comparator, means for applying the data in the shift register to one input of the comparator, means for applying data representative of the permitted maximum time interval (try) between control command signals to the other input of the comparator, means for repeatedly effecting a shift of the data in the shift register until such time as the output of the comparator changes state, and means responsive to said change of state for transferring the data in the shift register to said interpolator as a measure of the time interval (t,) between control command signals.
2. A numerical control system as claimed in Claim 1, wherein the shift register is controlled to left shift, and the data applied to the other input of the comparator is the inverse of the permitted maximum time interval (tm).
3. A numerical control system as claimed in Claim 1, wherein the shift register is controlled to right shift, the data initially
applied to the shift register is the inverse of the feedrate and the data applied to the other input of the comparator is the permitted maximum time interval (tm).
4. A numerical control system for automatic machinery wherein sequential control command signals are output from an interpolator, including data processing equipment for determining the rate at which said control command signals are calculated and generated, said data processing equipment comprising
a shift register for initially holding data representing the machinery feedrate,
first, second and third comparators,
means for applying data representative of the permitted maximum time interval (tm) between control commands to a first input of the first comparator,
means for applying to a first input of the second comparator data proportional in value by a factor K1 to the data applied to the first input of the first comparator, where 1AK,'A2 means for applying to a first input of the third comparator data proportional in value by a factor K2 to the data applied to the first input of the first comparator where K, 'AK2'A2 means for applying the data in the shift register to the second input of the first comparator,
means repeatedly effecting a shift of the data in the shift register until such time as the output of the first comparator changes state,
means responsive to the change of state of the first comparator for applying the data in the shift register to the second input of the second comparator,
means responsive to the change of state of the second comparator for applying the data in the shift register to the interpolator,
means responsive to the change of state of the first comparator for applying the data in the shift register to the second input of the third comparator,
means responsive to a change of state of the third comparator to apply to the interpolator the data in the shift register decreased by said factor K1, and
means coupled to the output of the third comparator to apply to the interpolator the data in the shift register decreased by said factor K2, in the absence of a change of state of the third comparator.
5. A numerical control system as claimed in Claim 4, wherein
5 K1 = 4
and
K2-1=3/2
6. A numerical control system as claimed in Claim 1 and substantially as hereinbefore described with reference to any one of the examples.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2253576A GB1568707A (en) | 1977-09-01 | 1977-09-01 | Data processing equipment |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2253576A GB1568707A (en) | 1977-09-01 | 1977-09-01 | Data processing equipment |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1568707A true GB1568707A (en) | 1980-06-04 |
Family
ID=10180965
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB2253576A Expired GB1568707A (en) | 1977-09-01 | 1977-09-01 | Data processing equipment |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1568707A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0121310A1 (en) * | 1983-03-31 | 1984-10-10 | Research Development Corporation of Japan | Apparatus for forming diverse shapes |
-
1977
- 1977-09-01 GB GB2253576A patent/GB1568707A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0121310A1 (en) * | 1983-03-31 | 1984-10-10 | Research Development Corporation of Japan | Apparatus for forming diverse shapes |
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| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |