Abstract: A sliding mode including a process of feeding back an amount of twist for controlling a servo loop is controlled by reading the position of a servomotor and the position of a mechanical actuator drivable by the servomotor (SP1), calculating an amount of twist which is an error (SP2), calculating a switching surface Suf with a value produced by filtering the amount of twist (SP3), and selecting a switching input with the produced value (SP4, SP5, SP6). The amount of twist is filtered by a filter which has a numerator and a denominator which are of a first order. The filter allows a system to be realized which suffers less vibration and is robust against inertia fluctuations.

Abstract: A feed rate control device for controlling the feeding operation of the electrode of a computerized numerical control type electric spark machine is equipped with an amplitude limiter, a regulator, and a proportional-plus-integral compensator. The amplitude limiter is capable of automatically limiting the amplitude of the input signal according to the moving situation of the electrode of the electric spark machine. By using of the amplitude limiter, the sensitivity of the system may be limited to a suitable level and therefore the stability of the whole system is increased. The proportional-plus-integral compensator is used to compensate the steady state error caused by improper low resolution when the output signal of the amplitude limiter is below an preliminary level. The regulator is used for facilitating the adjustment of the sensitivity of the system according to user's practical experiences.

Abstract: A collision detecting method for quickly securely detecting a collision between a driven body driven by a servomotor and an obstacle by using an observer, thereby preventing machine components from being damaged by the collision. An estimated distrubance torque (y) is obtained in accordance with a torque command (I) and an actual motor speed (.theta.) by means of the observer (50) formed of blocks (51 to 54) having transfer functions (Kt/J, K3, K4/S, 1/S), which depend individually on a torque constant, inertia, and parameters corresponding thereto, and a multiplier (61) having a transfer function (J.multidot.A) equivalent to the product of the inertia and a unit system conversion constant.

Abstract: A proportional plus integral controller operates an actuator in an HVAC system. The controller includes a setpoint circuit for providing a setpoint signal representative of a desired room temperature, a sensor circuit for providing a sensor signal representative of the actual room temperature, an error generator for generating an error signal proportional to the difference between the setpoint signal and the sensor signal, and an integrator for generating a control signal related to the time integral of the error signal. The setpoint and sensor signals are derived from a common voltage reference, so that accuracy of the controller is substantially independent of fluctuations of that reference. The integrator includes a capacitance multiplier that provides highly accurate integration of the error signal and a switch for selecting either proportional plus integral or proportional only control.

Abstract: A programmable PD servo compensator has the transfer function of the combination of a standard PD compensator in tandem with a second order low pass filter. The programmable PD servo compensator consists simply of a biquad filter having a single complex zero and a pair of conjugate complex poles. This servo compensator is comprised of two tandem connected operational amplifiers, each with a capacitor connected output to input across it. The tandem connection is effected by one switched-capacitor resistor between the output of the first amplifier to the input of the second. Another switched-capacitor resistor is connected between the PD compensator input and the input of the first amplifier. Yet another switched capacitor is connected between the PD compensator output and the input of the first amplifier.

Abstract: A servosystem comprising an adaptive digital controller (1) with an input signal (r.sub.t), an output control signal (u.sub.t) to the system (2) being controlled, and an input feedback signal (y.sub.t) from the system being controlled, the controller (1) incorporating an estimator (3) which operates recursively in response to the output control signal (u.sub.t) and feedback signal (y.sub.t) to estimate the values of parameters of a predetermined mathematical model (4) of the system being controlled and which makes use of a forgetting factor (.lambda.) to weight previous values of said parameters before these values are used in combination with current values of said output control and feedback signals (u.sub.t, y.sub.t) in each recursive estimation cycle, said output control signal (u.sub.

Abstract: The invention relates to control and, more particularly, to digital control of the relative positioning of an inertia system in translation or rotation.According to the invention, the position of the variable to be adjusted is defined digitally and this information is then processed to obtain the integral, to the first derivative and the second derivative. According to the invention, this second derivative is used to produce an automatic correction of the parameters to be applied to the integral, to the first derivative and to the position data in order to calculate the force or torque to be applied to the inertia system.Use for the adjustment of translation or rotation movements.

Abstract: An abnormality detecting method for a servo system capable of quickly detecting an abnormal condition even in a low rotation speed range is provided.While a digital servo control section (11-13) is executes a servo control operation for controlling the drive of a servomotor in accordance with a torque command (Tc) derived from a speed feedback (VA) and a speed command (Vc) corresponding to an actual position deviation (Er), a simulator (14) integrates a speed command (Vcs) equal to the product of a position loop gain (PG) and an estimated position deviation (Ers) obtained by subtracting a position feedback (PAS) from a movement command (Me). The simulator thus derives the position feedback (PAS), and an excessive error detecting section (15) compares the difference (Er-Ers) between the actual position deviation and the estimated position deviation with a predetermined value (As).

Abstract: A feedback controller inputs a reference signal instructing a controlled variable output from an object operated in accordance with a control signal and a feedback signal, to calculate the control signal such that the feedback signal is equal to the reference signal, and to supply the calculated control signal to the object. The controller has a transfer function Gf, and functions to generate the following response waveform f (t) due to a disturbance. That is, a response waveform of the controlled variable at the time when the disturbance is added to the controlled object is set to f (t), a response waveform of the feedback signal in an opened loop state, such that feedback of said controlled variable is turned off, is set to p (t), a relative degree of the disturbance is set to "d", and a relative degree of the controlled object is set to "g".

Abstract: In a control device for controlling a servo motor driving a robot arm, a target position command signal is input to a first operation section, which generates a speed command value for the speed feedforward. The target position command signal is also input to a delay section. A target position command signal delayed by a time period is obtained by the delay section and supplied to a second operation section. A positional deviation between the target position command signal and a position feedback signal is calculated by the second operation section. The obtained positional deviation is input to a third operation section and generated as a speed compensation command signal. A speed command signal obtained by addition of the speed feedforward signal and the speed compensation command signal is supplied to a servo driver for driving the servo motor.

Abstract: The invention relates to an electric control arrangement for generating analog manipulated variables, having at least one basic controller circuit having a particular controller structure. The transfer function of the basic controller circuit, which is determined by the controller structure, is established with respect to magnitude by means of controller parameters and is supplied with an analog control-difference signal formed from desired value and actual value. A digital adjusting arrangement is provided for simple adaptation to the particular controlling task with the least possible complexity as to computation. The digital adjusting arrangement 34, on the basis of digital input quantities, selects at least one basic controller circuit 12 having a particular controller structure from several basic controller circuits 12 and switches this basic controller circuit 12 into the analog control loop and/or allows a variation of the controller parameters.

Abstract: A limiter circuit of a servo motor control apparatus can perform limiter control in the right direction or reverse, direction or in both directions of a motor therefore. There is provided a microprocessor for outputting a switching signal by receiving rotating direction data from a motor rotating direction setter, and a converter for digital to analog converting the instantaneous limit value outputted from the microprocessor. Also included is a switching portion for selecting the output of instantaneous limit value outputted from the converter, and a limiter for limiting the amplitude the control voltage outputted the PID controller to within the scope of the instantaneous limit value selected according to the switching operation of the switching portion.

Abstract: A method for tuning P-, I- and D-type controller which is used in combination or individually to control a variable y of a process in a feedback system, which comprises making the integrating (I) and derivative (D) unit of the controller inoperative; increasing the proportional control gain K until a desired oscillation is obtained; calculating the ultimate gain Ku and ultimate period Tu in accordance with the amplitude and period measured from the oscillation; and setting the parameters of the PID controller in dependence upon the Ku and Tu values, wherein the control signal U resulting from the controller gain K is restricted to a range from a lower limit Umin to an upper limit Umax to avoid the system being operated in an unstable condition. An apparatus suitable for performing the present method is also disclosed.

Abstract: An autotuning procedure for a PID-type controller employs a low frequency sine wave as an exciting input and models the controlled system as a second order linear system. The system is tuned to a desired damping ratio by following an overdamped trajectory, in closed loop gain and phase lag space, to the target closed loop gain and phase lag values on a locus of a desired damping ratio as based on that modeling system.

Abstract: A discrete-type repetitive control unit which enables stable repetitive control even if a state variable of a controlled object is not observable, using time delay elements (Z.sup.-1). The number of time delay elements is equal to or greater than a value obtained by dividing a cycle period of a cyclic target input by a period of sampling the deviation between a controlled object output and the cyclic target input. Periodically applied to each of the time delay elements is a sum obtained by adding the product of the deviation and a first gain (h1, - - - , hn) associated with the time delay element, to the product of an input (u(k)) of the controlled object and a second gain (m1, - - - , mn) associated with the time delay element, and to an output (Wn(n+n), - - - , W1(k+1)) of a preceding element. The control unit periodically applies to the controlled object a sum (u(k)) obtained by adding the product of the deviation and a third gain (h0) to an output (W1(k)) of the last time delay element.

Abstract: A feed speed control method for a numerical control device in which a feed speed of a tool traveling along an instructed machining path is controlled in accordance with a machining program. The speed of each axis is derived (S2), and the acceleration of each axis is derived from a speed variation between adjacent blocks (S3). When the acceleration (.DELTA.Vx) is larger than a permissible acceleration (.DELTA.Vxmax) (S4), first ratios (K1) of the permissible accelerations to the accelerations are derived for individual axes (S5), and the smallest of the first ratios is selected. The command speed is multiplied by the square root of the smallest first ratio to derive an actual feed speed (S9). In this way, shock to a machine is reduced and an excessive load on a servomotor is reduced even when blocks continue for successive infinitesimal distribution distances, as in the case wherein a curve is approximated by the use of straight lines.

Abstract: A control system is provided for controlling a process system subject to an external disturbance by adjusting the value of a control amount output from the process system to a given target value. The system includes a target value generating unit for generating a given target value, and a main control unit receiving the target value and the control amount value for performing control operations to suppress fluctuation of the control amount value produced by the external disturbance and to adjust the control amount value to the given target value.

Abstract: The feedback gain for motor control for a control system in which the inertia of a load is greatly variable is adjusted. First, a feedback gain (K1) is determined. The value of feedback gain is calculated from a servomotor itself or the like, and selected so that the control loop will not oscillate (S1). A feed-forward gain (K) is determined according to a learning process with the feedback gain (K1) (S2). Then, a feedback gain (K1) is calculated from the feed-forward gain (K) (S3). Thereafter, a feed-forward gain (K) is determined again according to a learning process based on the feedback gain (S4). The second feed-forward gain (K) and the feedback gain (K1) are used to establish a control system. In this manner, a control system having an optimum feed-forward gain and an optimum feedback gain can be established.

Abstract: A device for positioning control includes a movable stage; an acceleration sensor disposed on the movable table; a feedback loop for controlling movement of the movable table; and an acceleration feedback loop provided in relation to an acceleration signal from the acceleration sensor, wherein the acceleration feedback loop is provided as an internal loop to the feedback loop.

Abstract: A numerical control unit for controlling the position of a movable part, such as a machine table, in response to input machining information. The unit employs a servo control loop that detects the values of the position, velocity, acceleration and motor current for the movable part at predetermined times. Using such detected values and, on the basis of a representative spring mass system model, values of inertia, mass, viscous friction and sliding friction can be calculated and used for automatically optimizing the gain and offset parameters applicable to control of the machine.

Abstract: When a workpiece is cut or otherwise machined by a machine using a servo motor control apparatus having a position feedback loop, a velocity feedback loop, and a current feedback loop, it is the common practice to preset the instructed current value to a voltage corresponding to friction torque when rotation of the motor is started or reversed. This is to compensate for the response delay of the motor introduced by the friction torque. The present invention relates to improvements in this technique. After the instructed motor velocity changes from a positive value, to a negative value or vice versa, or after the detected motor velocity changes from a positive value to a nonpositive value or from a negative value to a nonnegative value, the value of the integration element of a velocity control portion is reversed according to a function. The obtained output value is added to the instructed current value or to the integration term to compensate for the response delay, thus reducing machining error.

Abstract: In a feedback control system, a reference input element adjusts the amplitude and phase of a sinusoidal component of a command signal applied to the control system to cancel the transfer effects of the feedback loop, substantially eliminating error between a feedback signal and the common signal. The reference input element processes the sinusoidal component of a command signal through a network metaphor of a trigonometric identity. Adjustment of weights of the trigonometric identity permits arbitrary adjustment of the amplitude and phase of the command signal. A comparison of the command signal and the feedback signal, or of analogous signals, is used as an input to an automated trigonometric identity weight adjustment routine in the reference input element.

Abstract: A servo control system (100) for controlling a prime mover (16) to position a load (12) to a commanded position in accordance with the invention includes a position sensor (14) for providing a load position signal representative of a position of the load; a controller for producing a control signal controlling activation of the prime mover to cause the load to be positioned at the commanded position including a first summer (20) for producing a first difference signal equal to a difference between a position command specifying the commanded position and the load position signal which is applied to a proportional amplifier (22) and an integrator (24), a second summer (26) for producing a sum of outputs from the proportional amplifier and the integrator and a third summer (104) for producing the control signal which is equal to a difference between the sum of the outputs and a signal proportional to the load position signal.

Abstract: By means of a timer and by setting the compensation for the lag error, the correctness of automatic drift compensation in a position-loop controller is enhanced and the accuracy of position control is also improved. In the present invention, a method and a device for automatic drift compensation in a position-loop controller are disclosed which enable accurate displacement control so as to avoid inadvertent shutdowns of the system.

Abstract: A feedforward control apparatus capable of operating a servomotor smoothly and stably. A first feedforward controlled variable, obtained by differentiating a position command in a first feedforward term, is added to a control output of a position control loop, which varies depending on a positional deviation to obtain a speed command, whereby a response delay of the position control loop with respect to the position command is compensated to reduce control errors. Also, a second feedforward controlled variable, obtained by differentiating the first feedforward controlled variable in a second feedforward term, is added to a control output of a speed control loop, which varies depending on a speed deviation, whereby a response delay of the speed control loop with respect to the speed command is compensated to improve control stability, so that the servomotor and a mechanical system can be prevented from being shocked.

Abstract: A two degree of freedom PID controller which includes a setpoint filter for performing a derivative operation on a process disturbance signal in accordance with a setpoint value and a control value of a controlled system, thereby outputting a setpoint signal, a PI-control operation device for determining a deviation between the setpoint signal and the control value, and performing a PI-control operation on the deviation, thereby outputting a manipulative signal, and an adder for adding the process disturbance signal to the manipulative signal output by the PI-control operation device, thus obtaining a sum signal, and for supplying the sum signal to the controlled system.

Abstract: A servomotor control method controls a servomotor stably at a high speed. A control loop is switched from a PI control mode to an I-p control mode by varying a gain coefficient of a proportional arithmetic unit (1). This achieves a control process having the advantages of both the PI and I-p control modes.

Abstract: A control system having an open loop transfer function G expressed by a transfer function G.sub.2 of one control component having at least one integration element and a mass transfer function G.sub.1 of other control components and a saturation level of the other components expressed by the transfer function G.sub.2 set lower than that of the component expressed by G.sub.1.

Abstract: A method for control of servomotors includes limiting velocity feedforward as a second input to a velocity control loop in response to a velocity command, which is a first input, reaching a predetermined limit. Gain parameters for proportional and integral portions of a velocity-torque control loop and for the proportional and integral portions of the velocity feedforward loop may be adjusted independently to obtain varying control responses from the control system. The method is carried out in a microcomputer-based control module for an industrial controller.

Abstract: A digital controller comprising a deviation calculator, a positional P-controlling calculation device, a velocity-type I-controlling calculation device, a signal converter, and an adder unit. The deviation calculator for subtracts a process variable of an object from a set point variable, to obtain a deviation. The positional P-controlling calculation device performs positional P-calculation on the deviation obtained by the deviation calculator. The velocity-type I-controlling calculation device performs velocity-type I-calculation on the deviation. The signal-converting device converts the velocity-type I-calculation output of the velocity-type I-controlling algorithm device, into a positional I-signal. The adder unit adds the positional I-signal obtained by the signal-converting device and the positional P-calculation output obtained by the positional P-controlling algorithm device, thereby obtaining a manipulative variable. The manipulative variable value is supplied to the object to control the object.

Abstract: A vehicle speed control system comprises a vehicle speed controller (14) and an auxiliary engine speed controller (17) which keeps to the engine speed set by the first controller (14) and which controls the amount of fuel and/or air supplied to the vehicle engine. A comparator (13) compares actual and desired vehicle speed signals and is connected to the first controller (14), which produces a desired engine speed signal which is compared (16) with the actual engine speed signal from a sensor (21).

Abstract: In a position control system having force as a manipulated variable and position as a controlled variable, negative feedback of position and velocity is performed. Positive feedback of acceleration is performed through a first order lag circuit. Alternatively positive feedback of velocity is performed through a quasidifferential circuit. By the combination of negative and positive feedback, it is possible to stabilize vibration characteristics of the mechanism, which tends to make the control system stable, and to achieve position control with high gain, high response and high accuracy.

Abstract: A signal generator 16 is disclosed. The invention is adapted for use with industrial positioning systems and includes an integrating circuit 22 for integrating an input error signal to provide an output error signal and a limiting circuit 24, connected between the input and output of the integrating circuit 22 for limiting the output error signal. The output error signal is then used in a conventional manner to control a work piece or an implement. The integration of the low level input error signal rapidly increases the power delivered to the positioning system to overcome initial static friction. When the amplitude of the error signal indicates that the industrial apparatus is within a predetermined tolerance, the amplitude of output error signal decreases exponentially to diminish rapidly the power delivered to the positioning system. The apparatus will therefore be positioned within a given tolerance range.

Abstract: An integration-proportional controller in a servo-control system comprises in one aspect, an integrator for integrating a deviation of an input speed reference signal from a feedback signal fed back from an object to be controlled, and a proportional amplifier connected with the integrator for amplifying the feedback signal, the integrator including a clamping function in which an output value therefrom and an initial value for the next successive integration are changed, when the output value as a result of integration of the deviation is out of a predetermined proper output region, to the nearest boundary of the predetermined region value.

Abstract: A thermostat is disclosed which includes a Proportional-Integral-Derivative (PID) controller and a means for disabling the PID controller for selected periods. The PID controller is disabled during a temperature recovery period, which can be triggered by the occurrence of one or more of many preselected events. The PID controller is re-enabled when the thermostat setpoint less a void offset temperature is reached. To reduce error in future temperature recovery periods, the void offset temperature is adjusted after a temperature recovery by adding the amount of error to the void offset temperature to create a new void offset temperature for use in a next temperature recovery period.

Abstract: A method and system (10) for controlling radial movement of a machine tool, such as a turning machine, relative to a workpiece (11), is characterized by a digital filter (70, 72, 74) which produces a filtered final control signal which is a function of both radial position and velocity of a cutting tool (24) of the turning machine. The method and system (10) utilizes a tool position feedback signal which is compared with an initial control signal to produce a signal which is then digitally filtered to, in turn, provide the resulting final control signal. The surface geometry of the workpiece (11), such as a piston, is determined by a data matrix of angular, axial and radial position coordinants of the tool. An angular position signal representative of the angular position of the workpiece (11) and an axial position signal representative of the axial position of the cutting tool (24) relative to the workpiece (11) are both generated.

Abstract: A determination and control section of a process control system samples a set value, a difference value, a manipulated variable, and a controlled variable to determine a state of a process. When it is determined that the process is in an unstable state, an adaptive unit estimates a dynamic characteristic of the process, and calculate PID control parameters using a partial model matching method in a frequency region. When it is determined that the process is in an insufficient response state, the PID control parameter is regulated without operating the adaptive unit to decrease the gain of the process control system.

Abstract: A servo motor control device as provided in which the torque indication signal is not effected by the speed of rotation of the motor. This is accomplished by providing a torque corrector for converting an output of a speed detector into a torque correction signal. A subtractor is used for outputting the difference between a current instruction signal and the torque correction signal. The output of the subtractor is used as the torque indication signal.

Abstract: A servo motor controlling method for controlling both speed and current of a servo motor under digital control. An integration gain unit (22) and a loop proportional gain unit (26) of the current controlling loop are subjected to correction by respective gain units (23, 27) so as to be increased depending upon the rotational speed of the servo motor. Since a current loop gain is increased depending upon the rotational speed of the servo motor, the oscillation of the current loop does not occur at the time of low speed drive and stop, and the shortage of torque due to the lowering of the current loop gain at the time of high speed drive can be prevented.

Abstract: A control device for a servo motor comprises feedforward means for correcting a speed reference obtained by a position control device by a correction amount obtained on the basis of an objective position or an objective speed of the servo motor so that a response delay of the position control device for obtaining a reference speed necessary to control the rotation angle position of the servo motor to an objective rotation angle position is compensated for while restricting vibration.

Abstract: A digital servo system for causing a mechanical element (48) to track a desired path and hold various positions along the path and employing a lead/lag integrator (18) in parallel with a feedback control loop. The input to the integrator (18) is switched between velocity (V.sub.EK) error during pathtracking and position error (E.sub.K) during holding to increase the resistance of the mechanical element (48) to position changes caused by outside forces during both pathtracking and holding. The integrator function employed uses a term (U.sub.integrator(k-1)) representing a previous integrator output value to assist in smoothing perturbations caused by switching between position and velocity error.

Abstract: In an automatic control system including first and second control circuits, at least the second control circuit includes a proportional circuit and a differentiation circuit in addition to an integration circuit. When an object is controlled by switching from the first control circuit to the second circuit, an error signal between a target signal and a feedback signal is first applied to the integration circuit of the second control circuit, and after the lapse of predetermined time, the error signal is applied to the proportional circuit and the differentiation circuit of the second control circuit. With the constitution, jumping phenomenon is prevented which would be caused from the proportional circuit and the differentiation circuit.

Abstract: An apparatus and method for eliminating integrator windup in control systems having a control input, a feedback signal and an actuator that can saturate in response to dynamic non linearities such as slew rate limits. The apparatus of the invention is comprised of circuitry that determines the rate of change of the output of the integrator and compares it to predetermined maximum allowable rates of change. If these maximum allowable rates of change have been exceeded, the comparator circuitry generates a compensation error signal which when combined with normal error signal integrated by the compensator tends to reduce the rate of change on the output of the integrator.

Abstract: A method for process control to minimize hunting using a controller wherein a PID arithmetic operation is performed with respect to a deviation of a setting parameter and a processed variable fed back from a process, and a resultant manipulation variable is applied to the process including the steps of monitoring the waveforms of the setting parameter and the processed variable from the process to obtain an oscillation period of the deviation, identifying process characteristics of the process, obtaining a phase angle of a frequency response of an open-loop transfer function of a system from the oscillation period and the process characteristics, and detecting a hunting of the process by the magnitude of the phase angle.

Abstract: A first servo system (31) which feeds back at least position and speed and a second servo system (32) which effects integral control by feeding back position are connected in series. A first signal obtained by multiplying the output of the integral controller of the second servo system by a first gain is added to the position feedback signal of the first servo system, while a second signal obtained by multiplying the input of the integral controller of the second servo system by a second gain is added to the speed feedback signal of the first servo system. In this way, feedback control is effected using one mutual position detector, thereby eliminating the dynamic interference between the first and second servo systems, and thus enabling the two servo systems to be activated simultaneously.

Abstract: A tuning adjustment for a PI controller is disclosed which produces a desired response for a controlled variable in a selective control loop having an external reset feedback signal for anti-reset-windup protection. The desired control effect is evident in the time response of the controlled variables return to set point when a select switches signals and suddenly selects an output limited PI controller to control a process variable, and the selected controller assumes control of the process variable starting with its output at the limiting value. The tuning adjustment is implemented by combining the signal selected for controlling the process variable and a tuning factor for use as the reset feedback signal for the PI controller.

Abstract: A universal three-element digital control system is described which forms a proportional signal, an integral signal and a derivative (differential) signal from an error signal and combines such signals to provide a controlling output signal to a device being controlled. The error signal is the difference between the actual signal, representative of the actual condition of the device being controlled, and the setpoint, which is representative of the desired condition. The proportional signal is proportional to the error signal. The integral and differential signals can be approximated by combining the previous error signals with the present error signal. Offset and multiplying elements are provided by which each of the signals can be offset or proportionalized to customize the control system for a particular application.

Abstract: Method for adjusting the setting of a digital process regulator on the basis of the result obtained from a simple relay feedback experiment. When an adjustment of the regulator setting is to be made, the relay feedback is connected in the control feedback circuit instead of the regulator in order to cause self-oscillation. The self-oscillation signal is utilized to calculate the new setting of the regulator.

Abstract: This invention relates to an improved device for reducing the lag of position of a non-linear copying system or subsidiary controller for a regulation loop, which comprises a comparator establishing the difference which enters in a multiplier from which emerges a signal sent into another comparator elaborating the difference between this signal and the difference between the frequency and the frequency reference, so that the output of this comparator is introduced into the integral action circuit of the subsidiary controller.

Abstract: A servo motor control apparatus for a cutting machine comprises a position feedback loop, a speed feedback loop and a current feedback loop. A current command for the machine is preset to a voltage corresponding to a frictional torque when the motor starts rotation or changes rotating direction, in order to compensate for response lag of motor resulting from frictional torque. The response lag is improved and machining error is reduced by setting a value of a pertinent integral element in the controller comprising an integral element to zero. The sign of such value can be reversed at the moment that the motor operation start command or direction inversion command has changed to positive or negative from zero.