US 3,941,987 A · Method and apparatus for numerical control

Abstract

Method and apparatus for numerical control to produce contouring by simultaneous coordinated motions along two or more axes, characterized by the creation of desired velocity signals supplied as the primary inputs to velocity servos coupled to drive a member relatively along the respective axes. Although capable of practice by and susceptible of embodiment in other apparatus, a digital computer is physically organized and conditioned by a master program, and associated with an adjustable interrupt clock which measures off successive time periods .DELTA.T, so as to supply a changeable velocity command number signal to each servo proportional to the distance per .DELTA.T through which motion along the associated axis is to occur. This velocity command number is algebraically added to a theoretical position number to signal dynamically during each period .DELTA.T the axis position at which the member should reside; and the latter number is used with a dynamically signaled actual position number to re-compute and signal during each period the position error. The position errors are used as a trimming or adjusting term in the signals applied to the respective axis servos. When the signaled error exceeds a first threshold on any axis, the periods .DELTA.T are lengthened to reduce all axis velocities; when it exceeds a second threshold, the system is put into a holding mode. On the other hand, as the error is reduced below the second threshold, the system returns to the running mode and as the error is reduced below the first threshold the periods .DELTA.T are reduced to increase all axis velocities back to programmed values. The input signal applied to each axis servo includes a further historical adjustment term incrementally changed during any period when the error exceeds a predetermined value --all to the objective of making the axis servos (a) operate with substantially zero following error, (b) correct themselves if the position error becomes at all appreciable, or (c) stop if that error becomes intolerable. Because of the accuracy of velocity control, the system terminates any path segment for one block of command data when the number of elapsed periods .DELTA.T equals a precomputed number of time periods .DELTA.T required for the controlled member to travel the segment length at the commanded velocity expressed in distance per period. No comparison of command end point coordinates with actual end point coordinates is required. Automatic acceleration and deceleration is performed by starting the execution of a block of command data at the commanded velocity, and beginning an incrementing of the velocity command number during each period .DELTA.T after the number of elapsed periods becomes equal to the total of the periods for the entire block less the quantity required for the velocity to change from one block velocity to the next at the chosen incrementing or acceleration value.

Claims50

Dependent claims

The method of controlling the velocity and changing position and a member movable along an axis in accordance with numerical command data designating the desired velocity V, said method comprising:

a. measuring off successive periods .DELTA.T in actual time, the durations of such periods normally being .DELTA.TN but being adjustable,
b. deriving from said command data first signals representing a velocity number PRXC designating said velocity V in units of distance per .DELTA.TN,
c. producing second signals representing a theoretical position which said member should occupy along the axis, and changing said second signals by the represented amount PRXC once during each period .DELTA.T,
d. utilizing said second signals during each period .DELTA.T to produce third signals representing the then-existing error XERR between the theoretical position of said member and the actual position of said member,
e. driving said member along the axis at a velocity which is a function of both the velocity number PRXC and the error XERR as represented by said first and third signals, and
f. changing the durations of the periods .DELTA.T measured off according to step (a) in response to predetermined conditions which are dependent upon the magnitude of the error XERR as represented by said third signals.

3 more elements

The method of controlling the velocity and position of a member movable along an axis X in accordance with a block of numerical command data designating the desired velocity V.sub.x, said method comprising:

a. measuring off successive time periods in actual time, each period having a duration .DELTA.T with the value of the normal duration being .DELTA.TN,
b. deriving from said command data first electric signals digitally representing a number PRXC which designates said velocity V.sub.x in units of distance per .DELTA.TN,
c. representing by second digital electrical signals a number XTC to designate the theoretical instantaneous position of said member and adding the number PRXC thereto to form a new value of XTC once during each time period, such that XTC.sub.i = XTC.sub.i.sub.-1 + PRXC,
d. creating third digital electrical signals dynamically representing the actual instantaneous position XIN of said member as such actual position changes,
e. utilizing said second and third signals representing XTC and XIN to compute and to represent, by fourth digital electricals, the position error XERR = XTC - XIN once during each time period,
f. utilizing said first and fourth signals to drive said member along the X axis at a speed proportional to the sum of the then-existing numbers PRXC and XTRIM.sup.. XERR, where XTRIM is a predetermined gain factor, and
g. incrementally increasing the next time period .DELTA.T measured off when in any given time period the error XERR is lagging and greater in magnitude than a predetermined threshold value, whereby the velocity of the member is reduced to reduce the error.

4 more elements

The method of controlling the movement of a member along an X axis in accordance with a block of numerical command data designating the desired velocity V.sub.x, said method comprising:

a. measuring off successive time periods .DELTA.T in actual time, each such period having a normal duration of .DELTA.TN,
b. deriving from said command data first electric signals digitally representing a velocity number PRXC tantamount to the velocity V.sub.x but expressed in distance per .DELTA.TN,
c. creating second digital electrical signals representing a number XTC to designate the dynamically changing theoretical position of said member and utilizing said first signals to add the number PRXC thereto and form a new value of XTC once during each time period .DELTA.T,
d. sensing said member to create third digital electrical signals representing a number XIN dynamically designating the changing actual instantaneous position of the member,
e. employing said second and third signals to subtract the two numbers XTC and XIN and create fourth electrical signals digitally representing an error number XERR = XTC - XIN once during each period .DELTA.T,
f. causing the duration of the next period .DELTA.T to be increased by a predetermined amount in response to said number XERR exceeding a predetermined threshold value during any given period, and
g. applying a velocity servo coupled to said member an input signal proportional to the sum (PRXC + G.sub.2.sup.. XERR), where G.sub.2 is a preselected gain factor.

4 more elements

The method of relatively moving a member simultaneously along two or more axes X and Y over a path lying between first and second coordinate points P.sub.n.sub.-1 and P.sub.n in accordance with numerical command data designating the points and the desired velocity V.sub.n of travel, said method comprising:

a. measuring off successive periods .DELTA.T in actual time by means which are adjustable to vary the duration of the periods, the normal duration being .DELTA.TN,
b. deriving from said command data first and second sets of electric signals digitally representing numbers PRXC and PRYC which are equal to the distance which the member must move along the X and Y axes during each time period of duration .DELTA.TN to travel at axis velocities V.sub.x and V.sub.y producing the resultant path velocity V.sub.n,
c. converting said first and second sets of signals representing PRXC and PRYC into corresponding analog signals E.sub.x and E.sub.y,
d. applying said analog signals E.sub.x and E.sub.y to respective velocity servos respectively including motors to drive said member relatively along the X and Y axes at speeds directly related to the magnitudes of such signals,
e. producing third and fourth sets of digital signals numerically representing the instantaneous theoretical desired positions XTC and YTC of the member along the X and Y axes,
f. changing said third and fourth sets of signals during each measured-off time period by utilizing said first and second sets of signals to perform the algebraic additions XTC.sub.i = XTC.sub.i.sub.-1 + PRXC and YTC.sub.i = YTC.sub.i.sub.-1 + PYRC,
g. physically sensing, and numerically representing by fifth and sixth sets of signals during each time period, the actual relative positions XIN and YIN of said member along the X and Y axes, and
h. modifying said analog signals E.sub.x and E.sub.y by amounts proportional to the error differences XERR = XTC - XIN and YERR = YTC - YIN to cause corrective changes in velocities when position errors exist, and
i. adjusting said measuring-off means to increase the durations of said time periods .DELTA.T being measured off by a predetermined incremental amount whenever during any given period either of said error differences represents a lagging error of greater than a predetermined threshold value.

6 more elements

In a system for controlling the movement of a member along an axis X in accordance with a block of command data numerically signaled to directly or indirectly designate the desired velocity V.sub.x, said system comprising in combination:

a. means for measuring off successive periods .DELTA.T in actual time, with each period normally having a duration .DELTA.TN,
b. means responsive to said signaled command data for producing first electric signals digitally representing a number PRXC which designates said velocity V.sub.x in units of distance per .DELTA.TN,
c. means for producing second electric signals digitally representing a number XTC denoting the theoretical instantaneous position of said member and modifying such signals once during each period .DELTA.T to add the represented number PRXC, such that XTC.sub.i = XTC.sub.i.sub.-1 + PRXC,
d. means for producing third electric signals dynamically representing the actual instantaneous position XIN of said member as such position changes,
e. means responsive to said second and third signals for determining and creating, during each period .DELTA.T, fourth electric signals representing the position error XERR = XTC - XIN,
f. means responsive to said first and fourth signals for driving said member along the X axis at a speed proportional to the sum of the then-existing numbers PRXC and XTRIM.sup.. XERR, where XTRIM is a predetermined gain factor, and
g. means responsive to said fourth signals for modifying the operation of said means (a) to incrementally lengthen the following periods .DELTA.T when in any given time period the error XERR is lagging and exceeds a magnitude greater than a predetermined threshold value TH1.

4 more elements

In a system for relatively moving a member simultaneously along two or more axes X and Y along a path D.sub.n lying between first and second coordinate points P.sub.n.sub.-1 and P.sub.n in accordance with numerical command data signals designating the points and the desired velocity V.sub.n of travel, said system comprising in combination

a. means for measuring off successive periods .DELTA.T in actual time, the normal durations of such periods being .DELTA.TN,
b. means responsive to said command data signals for producing first and second sets of electric signals digitally representing velocity numbers PRXC and PRYC respectively equal to the distances which the member must move along the X and Y axes during each time period .DELTA.TN to travel at axis velocities V.sub.x and V.sub.y producing the resultant vector path velocity V.sub.n,
c. means for converting said first and second sets of signals into analog signals E.sub.x and E.sub.y corresponding to the numbers PRXC and PRYC,
d. two velocity servo systems respectively coupled to drive said member along the X and Y axes,
e. means for applying said analog signals E.sub.x and E.sub.y as inputs to respective ones of said velocity servo systems,
f. means for producing third and fourth sets of electric signals digitally representing the instantaneous theoretical positions XTC and YTC which said member should occupy along the X and Y axes,
g. means responsive to said first and second signal sets and to said third and fourth signal sets for changing the latter once during each period .DELTA.T, such that XTC.sub.i = XTC.sub.i.sub.-1 + PRXC and YTC.sub.i = YTC.sub.i.sub.-1 + PRYC,
h. means physically coupled to said member for producing fifth and sixth sets of electric signals digitally representing the actual positions XIN and YIN of said member along the X and Y axes,
i. means responsive to said third, fourth, fifth and sixth signal sets for modifying said analog signals E.sub.x and E.sub.y by amounts proportional to the error differences XERR = XTC - XIN and YERR = YTC - YIN to effect trimming adjustments in the axes velocities when position errors arise, and
j. means for adjusting said means (a) to incrementally lengthen the following time periods .DELTA.T when, in any given period .DELTA.T, either of said error differences XERR and YERR represents a lagging error of greater than a predetermined threshold value.

7 more elements

The method of controlling the velocity and the dynamically changing position of a member movable along an axis X in accordance with a block of numerical command data designating the desired velocity V, said method comprising:

a. measuring off successive periods .DELTA.T in actual time, with each period normally having a duration .DELTA.TN,
b. deriving, from said command data, first electric signals numerically representing a velocity number PRXC expressing said velocity V in dimensions of distance per time period .DELTA.TN,
c. creating second electric signals numerically representing the theoretical desired position XTC of said member and utilizing said first signals to change such second signals once during each period .DELTA.T by the amount of the velocity number PRXC,
d. creating third electric signals dynamically and numerically representing the actual position XIN of said member as it moves along the axis,
e. utilizing said second and third signals to create, by subtraction once during each period .DELTA.T, fourth electric signals dynamically and numerically representing the then-existing error XERR = XTC - XIN between the theoretical and actual positions of said member,
f. creating fifth electric signals numerically representing an adjustment number XBIAS,
g. utilizing said first, fourth and fifth signals to compute, once during each period .DELTA.T, and to produce sixth electric signals numerically representing the then-existing value of a speed number XDAC = PRXC + G.sub.2.sup.. XERR + XBIAS, where G.sub.2 is a preselected gain constant,
h. energizing a velocity servo in accordance with said sixth signals to drive said member at a velocity theoretically proportional to the XDAC number to make the member theoretically travel the distance PRXC during each period .DELTA.T,
i. comparing, during each period .DELTA.T, the number XERR represented by said fourth signals with a predetermined threshold value, and when the former exceeds the latter in any given period, incrementally increasing the durations of those .DELTA.T periods which follow, and
j. comparing, curing each period .DELTA.T, the number XERR represented by said fourth signals with a second predetermined value, and when the former exceeds the latter, incrementally changing said fifth signals to represent a new value for XBIAS, such that XBIAS.sub.i = XBIAS.sub.i.sub.-1 .+-. XKBIAS, where XKBIAS is a predetermined increment number.

7 more elements

In a system for controlling the velocity and dynamically changing position of a member movable along an axis X in accordance with a block of numerically signaled command data designating the desired velocity V, said system comprising the combination of:

a. means for measuring off successive periods .DELTA.T in actual time, with each period normally having a duration .DELTA.TN,
b. means responsive to said signaled command data for producing first electric signals numerically representing a velocity number PRXC expressing said velocity V in dimensions of distance per period .DELTA.TN,
c. means for creating second electric signals representing the theoretical desired position XTC of said member, and means responsive to said first signals for modifying said second signals to change the number XTC by the amount PRXC once during each period .DELTA.T,
d. means for creating third electric signals representing dynamically the changing actual position XIN of said member as it moves along the axis,
e. means responsive to said second and third signals to produce, by subtraction once during each period .DELTA.T fourth electric signals dynamically representing the then-existing error XERR = XTC - XIN between the theoretical and actual positions of said member,
f. means for creating fifth electric signals representing an adjustment number XBIAS,
g. means responsive to said first, fourth and fifth signals for producing anew during each period .DELTA.T sixth electrical signals numerically representing a speed number XDAC, where XDAC is equal to PRXC + G.sub.2.sup.. +XBIAS and G.sub.2 is a preselected gain constant,
h. a velocity servo coupled to drive said member along the axis, and means responsive to said sixth signals for energizing said servo in accordance with the value of the number XDAC,
i. means for comparing said fourth signals with a predetermined threshold TH1 and for modifying the operation of said means (a) to incrementally increase the durations of the following periods .DELTA.T when, during any given period .DELTA.T, the magnitude of said error XERR exceeds the threshold TH1, and
j. means responsive to said fourth signals, during any period .DELTA.T when said number XERR exceeds a predetermined magnitude, for incrementally changing said fifth signals to represent a new value of XBIAS, such that XBIAS.sub.i = XBIAS.sub.i.sub.-1 .+-. XKBIAS, where XKBIAS is a predetermined constant.

7 more elements

The method of controlling the velocity and dynamically changing position of a member movable along an axis X according to a block of command data numerically designating the desired velocity V and distance DX to be traveled, said method comprising:

a. measuring off in actual time successive period .DELTA.T which normally have a standard duration .DELTA.TN,
b. deriving from said command data and producing first digital signals numerically representing a velocity number PRXC expressing said velocity V in dimensions of distance per .DELTA.TN,
c. creating second digital signals numerically representing the theoretical instantaneous position XTC of said member,
d. utilizing said first and second signals to algebraically add once during each period .DELTA.T to change said second signals and change the position number XTC, such that XTC.sub.i = XTC.sub.i.sub.-1 + PRXC,
e. creating third digital signals numerically and dynamically representing the changeable actual position XIN of said member,
f. utilizing said second and third signals to algebraically subtract once during each period .DELTA.T to produce fourth digital signals numerically representing changing values of a position error number XERR = XTC - XIN,
g. creating fifth and sixth digital signals numerically representing a changeable adjustment number XBIAS and a predetermined increment number XKBIAS,
h. utilizing said first, fourth and fifth signals to compute, once during each period .DELTA.T, and produce seventh signals representing a speed number XDAC = G(G.sub.1.sup.. PRXC + XTRIM.sup.. XERR + XBIAS), where G is an overall gain factor, and G.sub.1 and XTRIM are individual term gain factors,
i. energizing a velocity servo in accordance with said XDAC signals to drive said member along the axis theoretically at a speed equal to the XDAC number,
j. comparing said fourth signals numerically with a predetermined error threshold value TH1 during each .DELTA.T, and in response to the number XERR representing a lag greater than said threshold, incrementally increasing the duration of the succeeding periods .DELTA.T which are measured off according to step (a), and
k. comparing said fourth signals with a predetermined constant during each .DELTA.T, and in response to the former exceeding the latter in magnitude, changing said fifth signal by said sixth signals to increment or decrement the signaled number XBIAS, such that XBIAS.sub.i = XBIAS.sub.i.sub.-1 .+-. XKBIAS.

8 more elements

In a system for controlling the velocity and dynamically changing position of a member movable along an axis X according to a block of command data signals numerically designating the desired velocity V and the distance DX to be traveled, said apparatus comprising in combination:

a. means for measuring off successive periods .DELTA.T in actual time, with such periods normally having a duration .DELTA.TN,
b. means responsive to said command data signals for producing first digital signals numerically representing a velocity number PRXC expressing said velocity V in dimensions of distance per .DELTA.TN,
c. means for creating second digital signals numerically representing the theoretical position XTC of said member XTC, including means responsive to said first signals for changing said second signals during each period .DELTA.T such that XTC.sub.i = XTC.sub.i.sub.-1 + PRXC,
d. means for creating third digital signals numerically representing the changeable actual position XIN of said member as it moves along the axis,
e. means responsive to said second and third signals to produce during each period .DELTA.T fourth digital signals numerically representing the error XERR between the theoretical and actual positions, such that XERR = XTC - XIN,
f. means for creating fifth and sixth digital signals numerically and respectively representing a changeable adjustment number XBIAS and a predetermined increment number XKBIAS,
g. means responsive to said first, fourth and fifth signals to produce anew during each period .DELTA.T seventh digital signals numerically representing a speed number XDAC, where XDAC = G[G.sub.1.sup.. PRXC + XTRIM.sup.. XERR + XBIAS] where G is an overall gain factor, and G.sub.1 and XTRIM are individual term gain factors,
h. a velocity servo coupled to drive said member along the axis, and means responsive to said seventh signals for energizing said servo in accordance with the value of the number XDAC,
i. means responsive to said fourth signals for modifying the operation of said means (a) to incrementally lengthen the periods .DELTA.T which follow any given .DELTA.T in which the error XERR represents a lag exceeding in magnitude a predetermined threshold value TH1, and
j. means responsive to said fourth and sixth signals to change said fifth signals to increment or decrement the number XBIAS during any period .DELTA.T in which the error XERR exceeds a predetermined value, such that XBIAS.sub.i = XBIAS.sub.i.sub.-1 .+-. XKBIAS.

7 more elements

The method of controlling the movement of a member along an axis X in accordance with a block of command data numerically designating the desired velocity V and extent DX of motion, said method comprising:

a. measuring off successive time periods .DELTA.T in actual time,
b. deriving from said command data electric signals digitally representing a number PRXC equal to DX/.DELTA.T and representing the desired velocity V in distance per .DELTA.T period,
c. converting said electrical signals into a corresponding analog signal,
d. applying said analog signal as an input to a velocity servo which includes a motor coupled to said member to drive the latter along said axis at a speed corresponding to that signal,
e. deriving from said command data electrical signals digitally representing a number LOOPC corresponding to (DX/V.sup.. .DELTA.T) and representing the number of time periods .DELTA.T required for said member to travel the distance DX at the velocity V,
f. producing electrical signals digitally representing a number NLOOP which begins at zero and changing such signals to increase such number by 1 each time a period .DELTA.T elapses while said member is being driven by said motor, and
g. continuing the driving of said motor according to steps (b), (c) and (d) until the signaled number NLOOP becomes equal to the signaled number LOOPC.

4 more elements

The method of controlling the movement of a member along plural axes X and Y in accordance with successive blocks of command data each numerically designating directly or indirectly desired path velocity V and extent of motion D, said method comprising:

a. measuring of successive time periods .DELTA.T in actual time,
b. deriving from said command data for a given block B.sub.n first and second sets of signals numerically representing axis velocity numbers PRXC and PRYC, said numbers expressing distances per .DELTA.T for velocities V.sub.x and V.sub.y which are the vector components of said velocity V,
c. converting said first and second sets of signals into corresponding analog signals E.sub.x and E.sub.y proportional to the numbers PRXC and PRYC,
d. applying said analog signals E.sub.x and E.sub.y as inputs to two corresponding velocity servos which respectively include motors coupled to drive said member along the X and Y axes,
e. deriving from said command data for the block B.sub.n a third set of signals numerically representing a quantity LOOPC of time periods required for the member to travel the distance D at the velocity V, such that ##EQU16## f. producing signals numerically representing a number NLOOP which begins at zero and changing such signals to increase such number by 1 each time a period .DELTA.T elapses while said member is being driven by said motors, and
g. comparing said signals representing LOOPC and NLOOPS, and when the two numbers represented thereby become equal, setting the NLOOPS signals to zero and continuing said steps (b)-(f) with data from the next block B.sub.n.sub.+1.

3 more elements

In a system for controlling the movement of a member along an X axis in accordance with a block of command data numerically signaled to directly or indirectly designate the desired velocity V.sub.x and extent DX of motion, said system comprising in combination:

1. means for measuring off successive periods .DELTA.T in actual time,
2. means responsive to said command data signals for creating a first set of digital signals numerically representing a number PRXC equal to DX/.DELTA.T and expressing the desired velocity V.sub.x in distance per .DELTA.T period,
3. means for converting said first set of signals into an analog signal E.sub.x,
4. a velocity servo system coupled to drive said member, and means for applying said analog signal as the input thereto,
5. means responsive to said command data signals for producing a second set of signals digitally representing the quantity LOOPC of periods .DELTA.T which are within a time span DX/V.sub.x,
6. means for producing a third set of signals digitally representing a number NLOOP which begins at zero and increases by 1 as each successive time period .DELTA.T elapses, and
7. means responsive to said second and third sets of signals for continuing said steps (2)-(6) until said number NLOOP equals or exceeds said number LOOPC.

4 more elements

In a system for controlling the movement of a member along plural axes X and Y in accordance with successive blocks B.sub.n, B.sub.n.sub.+1, B.sub.n.sub.+2 . . . of command data each numerically signaled to directly or indirectly designate the desired path velocity V.sub.n, V.sub.n.sub.+1 . . . and extent D.sub.n, D.sub.n.sub.+1 . . . of motion, said system comprising, in combination:

1. means for measuring off successive periods .DELTA.T in actual time,
2. means responsive to the command data signals of block B.sub.n for creating first and second sets of digital signals numerically representing numbers PRXC and PRYC respectively expressing distances per .DELTA.T for velocities V.sub.x and V.sub.y which are vector components of said velocity V,
3. means for converting said first and second sets of signals into analog signals E.sub.x and E.sub.y,
4. two velocity servo systems coupled to drive said member respectively along the X and Y axes, and means for applying said analog signals E.sub.x and E.sub.y as the respective inputs thereto,
5. means responsive to said command data signals for producing a third set of signals digitally representing the quantity LOOPC of periods .DELTA.T which will make up a time span T.sub.p equal to D.sub.n /V.sub.n,
6. means for producing a fourth set of signals representing a number NLOOP which begins as zero and responsive to said means (1) for increasing the represented number by 1 as each period .DELTA.T elapses, and
7. means for comparing said third and fourth sets of signals and for (a) setting said number NLOOP to zero and (b) transmitting the next block B.sub.n.sub.+1 command data signals to said means (2) and (5) after said number NLOOP has equaled or exceeded said number LOOPC.

4 more elements

a. measuring off successive periods .DELTA.T in actual time with the normal duration of each period being .DELTA.TN,
b. deriving from said command data first digital signals numerically representing a velocity number PRXC expressing said velocity V in dimensions of distance per time period .DELTA.TN,
c. creating second digital signals numerically representing a number XBIAS,
d. computing from said first and second signals, once during each period .DELTA.T, and creating third digital signals numerically representing a speed command number XDAC = G[PRXC + XBIAS], where G is a predetermined gain factor,
e. energizing a velocity servo in accordance with said XDAC signals to drive said member at a velocity theoretically corresponding to the number represented by such signals,
f. sensing and representing by fourth digital signals the numerical value of any error XERR between the theoretical position which the member should occupy during each period .DELTA.T and the position it actually occupies, and
g. utilizing said fourth signals to cause said second signals to be incrementally changed to increment the number XBIAS by a predetermined amount XKBIAS during any period .DELTA.T when the represented error exceeds a predetermined value, whereby said XBIAS signals progressively change the XDAC signals to bring the position error progressively toward zero if the PRXC signals fail to keep the position error zero.

4 more elements

Dependencies are inferred from the claim text.

Method and apparatus for numerical control

Life of this patent

Method and apparatus for numerical control

Life of this patent

Abstract

Claims50