DE1255775B - Digital position control, especially for numerically controlled machines - Google Patents

Description

GERMAN

PATENT OFFICE

EDITORIAL

G05f

German KL: 21c-46/54

Number: 1 255 775

File number: L 49614 VIII b / 21 c

Filing date: December 28, 1964

Opened on: December 7, 1967

Should a numerically controlled machine tool be used in at least two coordinates during machining are moved, a path control with an interpolator is generally used to create Intermediate values between two programmed nominal position values are required. A pure speed control the drives, d. H. Speed control of the moving machine part in the individual coordinate directions, works too imprecisely in the changing technological conditions to be able to control a position setpoint exactly. Controls of the type mentioned, in which in addition to the position control, which is essentially the shutdown of the Drives has to take over, a speed control operating at the same time is required Inaccurate despite considerable effort, because the position error is the time integral of the speed error μηα can be very large if only the integration time is sufficiently large.

The invention relates to a digital position control, in particular for numerically controlled machines, ζ. B. Machine tools at which the speeds with which the in at least two coordinate directions at the same time moving machine part is brought into its target position, depending on given Setpoints can also be regulated. It's the job to make sure that, too without creating intermediate values by an interpolator, the position setpoint with sufficient accuracy is approached.

According to the invention, this is achieved in that before reaching a certain range the speed control loops alone, then the position control loops are effective around the position setpoint are.

The setpoints of the speed control loops are in general for each coordinate on the Program carrier, e.g. B. a punched tape saved. A simple monitoring of the area in which the Switching of the control loops takes place, is then according to a special embodiment of the invention possible if the switching area forms a rectangle or square area with the position setpoint to be approached lies.

After switching to the position control loops, the speed control loops, which are then no longer necessary, can be subordinated to the position control loops in a manner known per se, ie the position control deviations form the setpoints of the speed control loops. The consequence of this is that the speed when entering the position setpoint can be matched exactly to the position control deviation, especially with digital position control
numerically controlled machines

Applicant:

Licentia Patent-Verwaltungs-G. m. b. H.,

Frankfurt / M., Theodor-Stern-Kai 1

Named as inventor:

Dr.-Ing. Heinz Günter Lott, Neu-Isenburg

and disturbance variables influencing the speed are also corrected.

The particular advantage of the invention is that it approximates the quality of a real path control with linear interpolation without the need for an interpolator.

The invention is explained in more detail with reference to the drawing showing an exemplary embodiment. It shows

F i g. 1 a speed-distance diagram,

F i g. 2 schematically the control circuit according to the invention,

F i g. 3 shows a graphical representation of the error in the event of deviations from the nominal path.

In Fig. 1, a tool (not shown) is to be moved during machining from point P ₁ with coordinates X ₁ ^ ₁ along straight line G ₁ to point P ₂ with coordinates x _z y ₂ . In addition to the coordinates of the new position setpoint, the program carrier also specifies speed setpoints v * 2> vy ₂ . Since the correct speed setpoints cannot be precisely specified for high accuracy requirements and the accuracy of the speed control is also limited, the resulting vector v _{r will} generally not coincide with the desired vector v _t , but will deviate somewhat from it, so that the position setpoint P _{2 will} not would be achieved. Therefore, as soon as the square area B _{2 is} touched at the point P ₂ ', a switchover to the position control loops takes place, which guide _{the tool exactly to the point P 2.} If this is reached,

709 707/445

the new position and speed setpoints X ₃ , y ₃ or VX ₃ , vy _{3 are} specified; the tool is controlled solely by the speed control loops back until it reaches the point P ₃ 'of the region _{B, etc.,} after which it is retracted from the position control loops in the target value _P3.

Of course, this method is not restricted to a movement in two coordinates. the Speed control loops can be subordinate to these after switching to the position control loops, so that the approach speed to the setpoint is in an exact ratio to the position control deviation can be brought.

In Fig. 2 the control arrangement is shown schematically. From the reader LS on the digital program carrier, not shown, z. B. a punched tape L, read the applied position and speed information and stored in the corresponding buffer ZLx, ZLy or ZVx, ZVy assigned to the individual coordinate directions. In addition, a value is brought into the memory UB , which corresponds to the dimensions of the switchover area. In a manner known per se, suitable digital measuring transducers for the actual position values MLx, MLy and the speed values MVx, MVy are attached to the machine tool W. The drives for the individual directions are labeled Ax and Ay.

At the beginning of a machining block, the drives of the machine W are first controlled by the speed control loops. The speed control deviations for the individual coordinate directions are determined in the subtraction elements VVx, VVy according to amount and sign and control the drives Ax and Ay via control amplifiers Vx and Vy.

The position control deviations are determined simultaneously for the individual coordinate devices in the subtraction elements VLx, VLy and are applied to the computing device R, which forms the deviations in χ and y . When this value is at the same time as the value stored in OB , ie when the switchover range around the position setpoint is reached, the switchover device S receives a command so that the position control deviations form the setpoints of the speed control loops. The drives are now controlled as a function of the position control loops via the now subordinate speed control loops until the setpoint is reached. After the new setpoints have been taken over from the punched tape, S switches over again, since the output value of R again differs from the value stored in ÜB.

In Fig. 3 shows how a movement of the machine on the path P ₁ , P ₂ , P ₃ affects the contour error /. Basically applies to

/: / = Ra (1 - cos <p),

when Ra represents the radius of the machining tool.

Furthermore, approximately applies

As_.
2 Ra

it follows

Ra (I ^ ¹

As *

The error can therefore be approximated to for small angles φ

As *
* ~ ZRa '

With a step size of s - 1 mm and a cutter radius of 12.5 mm, the error / z. B. 1/100 mm, that is, the control system according to the invention works very precisely.

Claims (5)

Patent claims: 1. Digital position control, especially in numerically controlled machines, in the the speeds at which the was moving in at least two coordinate directions at the same time Machine part is brought into its target position, also depending on predetermined target values are regulated, characterized that before a certain range around the nominal position value is reached, only the speed control loops, then the position control loops are effective. 2. Digital position control according to claim 1, characterized in that the setpoints of the Speed control loops are stored on a program carrier. 3. Digital position control according to claim 1 or 2, characterized in that the area around the Position setpoint, when it is reached the switchover from the speed control loops to the Position control circles are made by straight lines, preferably parallel to the coordinate directions, is limited. 4. Digital position control according to claim 1 or the following, characterized in that according to When the switchover range is reached, the position control deviations form the setpoints of the speed control loops. 5. Digital position control according to claim 1 to 3, characterized in that after taking effect the position control loops switch over if certain position control deviations are not reached at a reduced speed ' Considered publications:
German Auslegeschriften No. 1 079 170, 1 037 367, 007; Austrian Patent No. 230 479;
"Bulletin SEV" magazine, 1956, p. 85. 1 sheet of drawings 709 707/445 11.67 © Bundesdruckerei Berlin