Final servo control in NC systems

In a system for controlling the velocity and position of a member movable along an axis to track the position represented by a primary command signal (XCP) which is changed by amounts .DELTA.X during successive time periods .DELTA.T, and wherein the magnitude of the amount .DELTA.X may abruptly change, the improvement which comprises in combination:

• a. means for producing a secondary command signal (XSCP),
• b. means responsive to said primary and secondary command signals for producing an increment signal (.DELTA.XS) proportional to the difference (XCP - XSCP) therebetween,
• c. means for changing said secondary command signal (XSCP) by an amount represented by said increment signal once during each period .DELTA.T, and
• d. power servo means responsive to said secondary signal (XSCP) for moving said member to keep its position substantially in agreement therewith.

In a system for controlling the velocity and position of a member movable along an axis, the combination comprising:

• a. means for producing a first signal (.DELTA.X) designating an ideal desired velocity, such signal being abruptly and widely changeable from time to time,
• b. means for producing a second signal (XCP) designating an ideal desired position of the member,
• c. means responsive to said first signal for changing said second signal in a sense and at a rate corresponding to the sign and magnitude of the first signal,
• d. servo means responsive to a changeable input for moving said member to keep its actual position dynamically in substantial agreement with said input signal,
• e. means for producing a third signal (XSCP) designating a desired position of the member,
• f. means for changing said third signal at a rate proportional to, and in a sense corresponding to the sign of, the difference (XCP - XSCP) between the values of said second and third signals, and
• g. means for supplying said third signal as the input to said servo means (d).

In a system for controlling the velocity and position of a member movable along an axis, the combination comprising:

• a. means for measuring off successive periods .DELTA.T in actual time,
• b. means for producing a primary commanded position signal (XCP) which by sign and magnitude represents the desired position of said member,
• c. means for producing a velocity increment signal (.DELTA.X) which by sign and magnitude represents the desired velocity (.DELTA.X/.DELTA.T) of said member,
• d. means for algebraically combining said position and velocity signals to iteratively update the former during each period .DELTA.T, such that XCP.sub.i = XCP.sub.i.sub.-1 + .DELTA.X,
• e. means for producing a secondary position signal (XSCP),
• f. means for algebraically subtracting said secondary signal from said primary signal to produce an auxiliary velocity signal (.DELTA.XS) during each period .DELTA.T, so that .DELTA.XS = GF (XCP - XSCP) where GF is a gain factor less than 1.0,
• g. means for algebraically combining said auxiliary signal and said secondary signal during each period .DELTA.T to iteratively update the latter, such that XSCP.sub.i = XSCP.sub.i.sub.-1 + .DELTA.XS, and
• h. position servo means responsive to said secondary position signal XSCP to keep the controlled member dynamically positioned substantially in accordance therewith,
• whereby abrupt or wide changes in said velocity signal (XCP) result in more gradual changes in said secondary signal so as to permit said servo means more accurately to accelerate or decelerate the controlled member.

In a servo system which comprises:

• a. a member movable along a path,
• b. means for producing a first signal (XAP) indicative of the actual position of the member,
• c. means for producing a second signal (XSCP) indicative of the desired position of the member,
• d. means responsive to said first and second signals for producing a third signal (XPER) which is proportional to the error difference between the desired and actual positions of the member,
• e. means responsive to an input signal for driving said member along the path in a direction corresponding to the sign of such input signal, and
• f. means for coupling said third signal into said means (e) as said input signal, such means (f) being susceptible to spurious influences so as possibly to introduce into said input signal undesired offsets, whereupon the member's actual position is offset from the desired position when the input signal is reduced to zero by the closed loop servo action,
• the improvement which is characterized by
• 1. means for producing a fourth (XBAL) signal which is changeable in magnitude and sign,
• 2. means for algebraically combining said fourth signal with said third signal and applying the resultant (XVC) to said means (f), and
• 3. means for changing said fourth signal progressively whenever said third signal is not substantially zero,
• whereby said fourth signal is automatically adjusted to eliminate any undesired offset between the desired and actual positions of said member.

In a servo system for keeping a movable member dynamically positioned substantially in agreement with a changeable commanded position signal. the combination comprising:

• a. means for producing a changeable position command signal (XSCP),
• b. means for producing an acutal position signal (XAP) representing the actual position of the member,
• c. means responsive to said command and actual position signals as inputs for producing a position error signal (XPER) proportional to the difference (XSCP - XAP) between such inputs,
• d. means for driving said member is a direction and at a speed corresponding to the sign and magnitude of an input signal (XVC),
• e. means for producing a balance signal (XBAL),
• f. means responsive to said error signal and said balance signal for producing said input signal and applying it to said means (d), said input signal normally being proportional to the algebraic sum of said error and balance signals (XPER + XBAL) but such means (f) being susceptible of aging, drift and the like so as to create spurious offsets in said input signal causing it to depart from proportionality to said sum, and
• g. means for progressively increasing or decreasing said balance signal whenever said command signal is unchanging and said error signal is positive or negative and not substantially zero,
• thereby to compensate for said spurious offsets.

In a servo system for keeping a movable member dynamically positioned substantially in agreement with a changeable commanded position signal, the combination comprising:

• a. means for producing a first changeable digital signal (XSCP) numerically representing a desired, commanded position,
• b. means for producing a second changeable digital signal (.DELTA.XS) numerically representing a changeable incremental distance,
• c. means for measuring off successive equal periods (.DELTA.T) in actual time,
• d. means for algebraically adding during each said period (.DELTA.T) said second signal (.DELTA.XS) to said first signal (XSCP) to cause the represented commanded position to change at a rate (.DELTA.XS/.DELTA.T) determined by the magnitude of said incremental distance,
• e. means physically coupled to said member for producing a third changeable digital signal (XAP) numerically representing the actual position of said member,
• f. means for algebraically subtracting during each period (.DELTA.T) the third signal from the first signal to produce a fourth digital signal (XPER) numerically representing the error difference (XPER = XSCP - XAP) between the commanded and actual positions,
• g. means responsive to an input signal for driving said member in a direction and at a velocity corresponding to the sign and magnitude of such input signal,
• h. means for producing a fifth changeable digital signal (XBAL) representing a balance term,
• i. means for algebraically adding during each period (.DELTA.T) a changeable increment quantity of GBX.multidot.XPER to said fourth signal, where such quantity is proportional to the error difference represented by said fourth signal, so that said balance term changes at a rate and in a sense proportional to said error difference,
• j. means for inhibiting the operation of said means (i) except when said incremental distance represented by said second signals (.DELTA.XS) is substantially zero,
• k. means for algebraically combining said fourth and fifth signals during each period (.DELTA.T) to create a sixth digital signal (XVC) representing a compensated position error, and
• l. means for converting and coupling said sixth digital signals into an input signal applied to said means (g),
• whereby any spurious offsets introduced into said input signal by said means (1) are balanced out by changes in said fifth signals.

In a system for controlling the velocity and position of a member movable along an axis to track the position represented by a primary command signal (XCP) which is periodically changed by amounts .DELTA.X, the improvement which comprises in combination:

• a. means for producing a secondary command signal (XSCP),
• b. means responsive to said primary and secondary command signals for producing an auxiliary signal (.DELTA.XS) which varies according to the difference (XCP - XSCP) between said command signals,
• c. means for changing said secondary command signal at a rate and in a sense corresponding to the magnitude and sign of said auxiliary signal,
• d. means for producing a feedback signal (XAP) which by its value represents the instantaneous actual position of the controlled member,
• e. means for producing an arror signal (XPER) proportional to the difference (XSCP - XAP) between the secondary command signal and the feedback signal,
• f. means for producing a balance signal (XBAL),
• g. means for changing the balance signal in a sense and at a rate corresponding to the sign and magnitude of said error signal whenever said auxiliary signal is substantially zero, and
• h. power means responsive to an algebraic sum function of said error and balance signals (XPER + XBAL) for driving said member at a velocity corresponding in magnitude and direction.

In a system for controlling the velocity and position of a member movable along an axis to track the position represented by a primary command signal (XCP) which is changed by amounts .DELTA.X during successive time priods .DELTA.T, the improvement which comprises in combination:

• a. means for producing a secondary command signal (XSCP),
• b. means responsive to said primary and secondary command signals for producing an increment signal (.DELTA.XS) proportional by a factor of less than 1.0 to the difference (XCP - XSCP) therebetween,
• c. means for changing said secondary signal by the amount represented by the increment signal during each period .DELTA.T, so that XSCP.sub.i = XSCP.sub.i.sub.-1 + .DELTA.XS,
• d. means for producing a feedback signal (XAP) which by its value represents the instantaneous actual position of the controlled member,
• e. means for producing an error signal (XPER) proportional to the difference (XSCP - XAP), between the secondary command signal and the feedback signal,
• f. means for producing a balance signal (XBAL),
• g. means for changing said balance signal by an amount proportional to the error signal (XPER) during each period .DELTA.T whenever said increment signal (.DELTA.XS) is substantially zero, so that XBAL.sub.i = XBAL.sub.i.sub.-1 + GBX.multidot.XPER, and
• h. power means responsive to the algebraic combination of said error and balance signals for driving said member at a velocity substantially proportional to such combination (XPER + XBAL).