METHOD AND CONTROL DEVICE FOR CONTROLLING A ROTATIONAL SPEED

Abstract

Various aspects of the present disclosure are directed to, for example, methods of controlling a rotational speed of a maching. in one example embodiment, the method includes the steps of: generating a rotational speed reference variable for a controller from a rotational speed setpoint value; determining an adapted rotational speed setpoint value which considers a rotation angle actual value and a rotation angle setpoint value determined on the basis of the rotational speed setpoint value; and switching the rotational speed reference variable between the rotational speed setpoint value and the adapted rotational speed setpoint value as a function of the rotational speed.

Claims

1. Method for controlling a rotational speed of a machine including the following steps: generating a rotational speed reference variable for a controller from a rotational speed setpoint value; determining an adapted rotational speed setpoint value which considers a rotation angle actual value and a rotation angle setpoint value determined on the basis of the rotational speed setpoint value; switching the rotational speed reference variable between the rotational speed setpoint value and the adapted rotational speed setpoint value as a function of the rotational speed.

2. The method according to claim 1, characterized in that the switching is carried out according to a switching characteristic curve including a transition phase, the rotational speed reference variable corresponding to a linear combination of the rotational speed setpoint value and the adapted rotational speed setpoint value in the transition phase.

3. The method according to claim 1, characterized in that the adapted rotational speed setpoint value is determined from a deviation of the rotation angle actual value from the rotation angle setpoint value.

4. The method according to claim 1, characterized in that the rotation angle setpoint value is determined as an integrated and normalized value from the rotational speed setpoint value.

5. The method according to claim 1, characterized in that the rotation angle actual value is determined as a scaled and normalized value from a rotation angle raw signal.

6. The method according to claim 1, characterized in that a rotational speed feedback variable of the control system is switched between a general rotational speed measurement value and a high-resolution rotational speed measurement value as a function of the rotational speed.

7. The method according to claim 6, characterized in that the switching is carried out according to a switching characteristic curve including a transition phase, the rotational speed feedback variable corresponding to a linear combination of the general rotational speed measurement value and the high-resolution rotational speed measurement value in the transition phase.

8. A control arrangement for controlling the rotational speed of a machine, the control arrangement comprising: an integrating element configured and arranged to determine a rotation angle setpoint value from a rotational speed setpoint value; an adapting element is configured and arranged to utilize a rotation angle actual value and the rotation angle setpoint value to determine an adapted rotational speed setpoint value; and a setpoint value switching element configured and arranged to switch a rotational speed reference variable between the rotational speed setpoint value and the adapted rotational speed setpoint value as a function of the rotational speed.

9. The control arrangement according to claim 8, characterized in that the setpoint value switching element is further configured and arranged to carry out the switching process according to a switching characteristic curve, in which the rotational speed reference variable is determined as a linear combination of the rotational speed setpoint value and the adapted rotational speed setpoint value.

10. The control arrangement according to claim 8, wherein the adapting element is configured and arranged to determine the adapted rotational speed setpoint value from a deviation of the rotation angle actual value from a rotation angle setpoint value.

11. The control arrangement according to claim 8, wherein the integrating element is configured and arranged to determine the rotation angle setpoint value as an integrated and normalized value from the rotational speed setpoint value.

12. The control arrangement according to claim 8, further including an angle signal processing element configured and arranged to determine the rotation angle actual value as a scaled and normalized value from a rotation angle raw signal.

13. The control arrangement according to claim 8, characterized in that the control arrangement further includes an actual value switching element configured and arranged to switch a rotational speed feedback variable of the control system between a general rotational speed measurement value and a high-resolution rotational speed measurement value as a function of the rotational speed.

14. The control arrangement according to claim 13, characterized in that the actual value switching element is configured and arranged to carry out the switching process according to a switching characteristic curve in which the rotational speed feedback variable is determined as a linear combination of the general rotational speed measurement value and the high-resolution rotational speed measurement value.

15. The method of claim 1, wherein the machine is a load machine on a test bench.

16. The control arrangement of claim 8, wherein the machine is a load machine on a test bench.

17. The method of claim 2, wherein the transition phase of the switching characteristic curve is a ramp-like transition phase.

18. The method of claim 7, wherein the transition phase of the switching characteristic curve is a ramp-like transition phase.

19. The control arrangement of claim 9, wherein the switching characteristic curve includes a preferably ramp-like transition phase.

20. The control arrangement of claim 14, wherein the switching characteristic curve includes a preferably ramp-like transition phase.

Description

[0018] In the following, the present invention is described in greater detail with reference to FIGS. 1 to 5 which, by way of example, show schematic and non-limiting advantageous embodiments of the invention. In the drawings,

[0019] FIG. 1 is a schematic view of a control arrangement according to a first embodiment,

[0020] FIG. 2 is a block diagram of a setpoint value switching element of the control system according to an advantageous embodiment,

[0021] FIG. 3 is a block diagram of part of the control system in a more detailed view,

[0022] FIG. 4 is a block diagram of an actual value switching element according to a further embodiment of the control system according to the invention, and

[0023] FIG. 5 is a schematic view of a control arrangement according to a second embodiment.

[0024] FIG. 1 shows the control system of a load machine 2 of a test bench, the load machine 2 being connected to a test object (not shown) via a shaft. The rotational speed n at which the shaft on the load machine 2 rotates is the controlled variable. The rotational speed n is measured by means of a sensor arrangement 9 and fed back to a controller 3 as a rotational to speed feedback variable n.sub.r. In the controller 3, the deviation of the rotational speed feedback variable n.sub.r from a rotational speed reference variable n.sub.lead is determined and supplied as a control difference to a control element 10 which generates a manipulated variable for the load machine 2 in accordance with a defined control strategy.

[0025] During “normal” operation, i.e. above a certain minimum rotational speed n.sub.min, the rotational speed reference variable n.sub.lead conventionally corresponds to a rotational speed setpoint value n.sub.set, which is generated, for example, by a system controller or a simulation.

[0026] In the case of known control methods for load machines on test benches, there is a reduction in control quality at low rotational speeds n, in particular when accelerating from a standstill and decelerating to a standstill. In order to improve the control quality, according to the invention, the rotational speed reference variable n.sub.lead is therefore switched to an adapted rotational speed setpoint value n.sub.adapt by a setpoint value switching element 4, which is upstream of the controller 3, when the rotational speed n is below the minimum rotational speed n.sub.min. In the case shown, the comparison with the minimum rotational speed n.sub.min is carried out on the basis of the rotational speed setpoint value n.sub.set, but the comparison could also be carried out, for example, on the rotational speed feedback variable n.sub.r. The adapted rotational speed setpoint value n.sub.adapt ensures a high and stable control quality, even in the slow rotational speed range. The minimum rotational speed n.sub.min is selected such that the critical ranges of low rotational speeds are completely covered and that switching takes place in a rotational speed range that is as uncritical as possible.

[0027] The adapted rotational speed setpoint value n.sub.adapt is formed by an adapting element 5 on the basis of a rotation angle evaluation, in which a rotation angle setpoint value φ.sub.set determined by an integrating element 6 from the rotational speed setpoint value n.sub.set is compared with a rotation angle actual value φ.sub.act determined on the basis of the sensor arrangement 9 (or a corresponding other measuring arrangement). By means of this adapted rotational speed setpoint value n.sub.adapt, the rotational speed reference variable n.sub.lead is adjusted in the low rotational speed range as a function of how the load machine 2 follows its ideal (angular) position over time. The rotation angle actual value φ.sub.act is determined in the shown embodiment from a rotation angle raw signal φ.sub.raw measured by the sensor arrangement 9, whereas an angle signal processing element 7 generates the rotation angle actual value φ.sub.act in a form matching the rotation angle setpoint value φ.sub.set from the rotation angle raw signal φ.sub.raw.

[0028] The use of a position signal (i.e. angle signal) prevents the problem of the resolution of the measured rotational speed signal (i.e. the signal on which the rotational speed feedback variable n.sub.r is based) being too low at low rotational speeds and also has the advantage that, in the case that a rotational speed setpoint value=0 rpm, the rotational speed cannot drift away due to the connection to the absolute value of the angle.

[0029] FIG. 2 shows an alternative embodiment of the setpoint value switching element 4. In this case, the rotational speed reference variable n.sub.lead is switched between the rotational speed setpoint value n.sub.set and the adapted rotational speed setpoint value n.sub.adapt according to a switching characteristic curve 11 which provides a ramp-like transition phase t. A minimum rotational speed n.sub.min is also defined in this case (both for a positive rotational direction n.sub.min.sup.+ and for a negative rotational direction n.sub.min.sup.−). At rotational speeds n, of which the absolute value is above the minimum rotational speed n.sub.min, the setpoint value switching element 4 in turn uses the rotational speed setpoint value n.sub.set as the rotational speed reference variable n.sub.lead. As soon as the absolute value of the rotational speed falls below the minimum rotational speed n.sub.min, the setpoint value switching element 4 creates the rotational speed reference variable Read as a linear combination of the rotational speed setpoint value n.sub.set and the adapted rotational speed setpoint value n.sub.adapt within the transition phase t. If the absolute value of the rotational speed is below the transition phase, the adapted rotational speed setpoint value n.sub.adapt is used as the rotational speed reference variable n.sub.lead.

[0030] FIG. 3 shows an advantageous embodiment of part of the control system outlined in FIG. 1, the integrating element 6, the angle signal processing element 7, and the adapting element 5 being shown in greater detail. With reference to FIG. 3, the generation of the adapted rotational speed setpoint value n.sub.adapt will now be explained using this specific embodiment.

[0031] The integrating element 6 generates the rotation angle setpoint value φ.sub.set from the rotational speed setpoint value n.sub.set as an integrated value normalized to an angle range of between 0° and 360°. In order to be able to directly compare the rotation angle actual value (pad with this value, the rotation angle raw signal φ.sub.raw is scaled in the angle signal processing element 7 (scaling element 12) and also normalized to an angle range of between 0° and 360° in a normalizing element 13.

[0032] In the adapting element 5, a rotation angle difference φ.sub.delta is formed from the rotation angle setpoint value φ.sub.set and the rotation angle actual value φ.sub.act. The rotation angle difference φ.sub.delta is normalized to an angle range of between −180° and +180° in a second normalizing element 14 and is amplified in an amplifier element 15. In order to obtain the adapted rotational speed setpoint value n.sub.adapt, the signal is also subjected to a gradient correction 16 and is limited in a value limitation 17.

[0033] FIG. 4 is a detailed view of an actual value switching element 8 according to an alternative embodiment of the invention. The actual value switching element 8 shown in FIG. 4 can be used in addition to the control system described above or, optionally, also “on its own,” i.e. in conjunction with a conventional control system. The functionality of the actual value switching element 8 is based on the concept of using a high-resolution measurement signal as the rotational speed feedback variable n.sub.r at low speeds, which prevents the problems of the measurement signals normally used, which originate from low-resolution measuring systems. Nevertheless, the advantages offered by these low-resolution measuring systems in higher rotational speed ranges should still be usable.

[0034] The actual value switching element 8 has two input values, each of which originates from a measuring device, for example the sensor arrangement 9, and an output value which is fed back into the control system as a rotational speed feedback variable n.sub.r. The first input value is a general rotational speed measurement value n.sub.sr which originates, for example, from a conventional rotational speed measuring device, for example an encoder. The general rotational speed measurement value n.sub.sr can originate, for example, from an encoder having a line count of 512 and the input type “1-edge evaluation”. At low rotational speeds, the time intervals between the individual measurement points naturally increase and can ultimately lead to problems with regard to the control quality. For example, such an encoder generates less than 9 pulses per second at a rotational speed of 1 rpm (this corresponds to an angle that increases or decreases at 6°/s). If the absolute value of the rotational speed is below a minimum rotational speed n′.sub.min, the actual value switching element 8 therefore switches from the general rotational speed measurement value n.sub.sr to a high-resolution rotational speed measurement value n.sub.hr, which originates from a high-resolution measurement sensor. This is the second input value of the actual value switching element 8.

[0035] The high-resolution rotational speed measurement value n.sub.hr can be obtained, for example, by rotational speed measuring systems which provide a high-resolution signal, for example a signal having a frequency of 100 kHz or more, even at a rotational speed of 0 rpm. Examples of such high-resolution speed measurement systems include an HMCR16 rotary encoder together with an HEAG-158 or HMCP 16A signal splitter, which are available from Baumer-Hubner. Although such sensors have the advantage that they produce a correct measured value even at very low rotational speeds, they can no longer be used above a certain maximum rotational speed because the values become imprecise. Switching between the high-resolution speed measurement value n.sub.hr and the general rotational speed measurement value n.sub.sr takes place in a rotational speed range in which the reliable working ranges of the two sensors overlap, such that, when switching at the minimum rotational speed n′.sub.min, the two values, i.e. the general rotational speed measurement value n.sub.sr and the high-resolution rotational speed measurement value n.sub.hr match. This prevents jumps in the value of the rotational speed feedback variable n.sub.r when switching. In addition, as already described in connection with the setpoint value switching element 4, the switching process can take place with a ramp-like transition phase t′, in which the value for the rotational speed feedback variable n.sub.r is created as a linear combination of the high-resolution rotational speed measurement value n.sub.hr and the general rotational speed measurement value n.sub.sr.

[0036] The minimum rotational speed n′.sub.min used by the actual value switching element 8 can match the minimum rotational speed n.sub.min used by the setpoint value switching element 4 (if these two components are used together in a conntrol system), but the values can also differ. In the representation in the drawings, the same absolute value is used in each case for the positive minimum rotational speed n.sub.min.sup.+or n′.sub.min.sup.+ and the negative minimum rotational speed n.sub.min.sup.− or n′.sub.min.sup.−. However, this is not a mandatory requirement and these values can also differ from one another. The ramp-like transitions shown in the drawings illustrate a preferred embodiment due to the simple implementation possibilities; however, it is clear that other types of transitions or switching characteristic curves can also be used, for example to implement a stepped switching or a curved switching without points of discontinuity, if this is advantageous.

[0037] FIG. 5 shows a control arrangement 1 in which all of the variants described above are implemented together. The sensor arrangement 9 in this case comprises a plurality of sensors and generates a general rotational speed measurement value n.sub.sr, a high-resolution rotational speed measurement value n.sub.hr and a rotation angle raw signal φ.sub.raw in order to provide these values to the actual value switching element 8 and the angle signal processing element 7.

VARIABLES

[0038] rotational speed n

[0039] rotational speed setpoint value n.sub.set

[0040] rotational speed reference variable n.sub.lead

[0041] adapted rotational speed setpoint value n.sub.adapt

[0042] rotational speed feedback variable n.sub.r

[0043] general rotational speed measurement value n.sub.sr

[0044] high-resolution rotational speed measurement value n.sub.hr

[0045] to minimum rotational speed n.sub.min

[0046] rotation angle actual value φ.sub.act

[0047] rotation angle setpoint value φ.sub.set

[0048] rotation angle raw signal φ.sub.raw

[0049] rotation angle difference φ.sub.delta

REFERENCE SIGNS

[0050] control arrangement 1

[0051] load machine 2

[0052] controller 3

[0053] setpoint value switching element 4

[0054] adapting element 5

[0055] integrating element 6

[0056] angle signal processing element 7

[0057] actual value switching element 8

[0058] sensor arrangement 9

[0059] control element 10

[0060] switching characteristic curve 11, 11′

[0061] scaling element 12

[0062] standardizing element 13

[0063] second standardizing element 14

[0064] amplifier element 15

[0065] gradient correction 16

[0066] value limitation 17

[0067] transition phase t, t′