METHOD AND CONTROL DEVICE FOR CONTROLLING A SPEED

Description

[0001] The invention relates to a method for controlling the speed of a test bench load machine, wherein a speed command variable for a controller is generated from a speed setpoint. Furthermore, the invention relates to a control arrangement for controlling the speed of a test bench load machine.

[0002] With conventional speed sensors (particularly incremental encoders), as they are commonly used with electrical load cells on test benches, the measuring range around zero rpm and at exactly zero rpm is generally only inadequately covered. Below a certain minimum speed, the speed-dependent deviation between the absolute value and the incremental signal can no longer be simply neglected. The poorly resolved speed signal subsequently leads to control problems. The required control quality cannot be achieved. This problem of speed control at low speeds arises on automotive test benches, especially when tests are to be carried out from a standstill or at very low speeds. The problem is also known from powertrain test benches, where the load cell acts at wheel level. Since the increased introduction of electrified components (e.g.Electric motors or hybrid drives) the problem is also increasingly occurring on engine test benches.

[0003] The object of the present invention is to improve the control of the speed of a machine with regard to its performance even at speeds close to zero or during control processes from or to standstill.

[0004] According to the invention, these and other objects are achieved by a method as claimed in claim 1. As a result, at low speeds the speed setpoint for the control can be adapted depending on how the controlled machine follows the ideal (angular) position over time. At higher speeds, for example if the speed sensor has a sufficiently high resolution, the control switches to the conventional control method. The use of a position signal (i.e. angle signal) at low speeds also has the advantage that with a speed setpoint of zero rpm the speed cannot drift due to the reference to the absolute value of the angle. The speed at which the switching occurs is selected to be high enough that the control functions sufficiently well even without an adapted speed setpoint.In this range, no deviation of the actual angle of rotation from the setpoint angle of rotation is to be expected, so that no sudden changes in the speed command variable are to be expected when switching over.

[0005] Advantageously, the switching can be carried out according to a switching characteristic with a preferably ramp-like transition phase, wherein the speed command variable during the transition phase corresponds in particular to a linear combination of the speed setpoint and the adapted speed setpoint. The resulting ramp-like control transition is advantageous for reasons of control stability, while preventing the occurrence of torque surges.

[0006] In a preferred embodiment, the adapted speed setpoint can be determined from a deviation of the actual rotation angle value from the desired rotation angle value. This can be achieved using a simple summing element in conjunction with appropriate signal conditioning.

[0007] Advantageously, the angle of rotation setpoint can be determined as a standardized value from the speed setpoint.

[0008] According to a further advantageous embodiment, the actual angle of rotation value can be determined as scaled and standardized values ​​from a raw angle of rotation signal. This allows the desired angle of rotation value and the actual angle of rotation value to be easily correlated with each other.

[0009] In an advantageous embodiment, according to the invention, a speed feedback variable of the control system can be switched between the general speed measurement value and a high-resolution speed measurement value depending on the speed. This feature allows the control accuracy to be further increased, since a high-resolution speed measurement value is used in the low speed range.

[0010] Advantageously, the switching can be carried out according to a switching characteristic with a preferably ramp-like transition phase, wherein, during the transition phase, the speed feedback variable corresponds in particular to a linear combination of the general speed measurement value and the high-resolution speed measurement value. This, in turn, serves to ensure control stability and prevent torque surges.

[0011] The objects of the invention are further achieved by a control arrangement according to claim 8. This control arrangement allows an advantageous implementation of the method disclosed above.

[0012] Advantageously, the setpoint switching element can be designed to carry out the switching process according to a switching characteristic with a preferably ramp-like transition phase in which the speed command variable is determined in particular as a linear combination of the speed setpoint and the adapted speed setpoint.

[0013] In an advantageous embodiment of the invention, the control arrangement can have an adapter element which determines the adapted speed setpoint from a deviation of the actual rotation angle value from a rotation angle setpoint.

[0014] In a further advantageous embodiment, the control arrangement can have an integrating element which determines the rotation angle setpoint as a standardized value from the speed setpoint.

[0015] According to a further advantageous embodiment, the control arrangement can have an angle signal conditioning element which determines the actual angle of rotation value as a scaled and standardized value from a raw angle of rotation signal.

[0016] Advantageously, the control device can have an actual value switching element which switches a speed feedback variable of the control between the general speed measurement value and a high-resolution speed measurement value depending on the speed.

[0017] In a further advantageous embodiment according to the invention, the actual value switching element can be designed to carry out the switching process according to a switching characteristic with a preferably ramp-like transition phase in which the speed feedback variable is determined in particular as a linear combination of the general speed measured value and the high-resolution speed measured value.

[0018] The present invention is described below with reference to the Figures 1 to 2 which show exemplary, schematic and non-limiting advantageous embodiments of the invention. Fig.1 a schematic representation of a control arrangement according to a first embodiment, Fig. 2 a block diagram of a setpoint switching element of the control according to an advantageous embodiment, Fig. 3 a block diagram of part of the control system in a more detailed representation, Fig. 4a block diagram of an actual value switching element according to a further embodiment of the control according to the invention and Fig. 5 a schematic representation of a control arrangement according to a second embodiment.

[0019] Fig. 1 shows the control of a dynamometer 2 of a test bench, wherein the dynamometer 2 is connected to a test specimen (not shown) via a shaft. The speed n, at which the shaft on the dynamometer rotates, is the controlled variable. The speed n is measured via a sensor arrangement 9 and fed back to a controller 3 as a speed feedback variable nr. In controller 3, the deviation of the speed feedback variable nr from a speed reference variable n lead is determined and fed as a control difference to a control element 10, which generates a manipulated variable for the dynamometer 2 according to a defined control strategy.

[0020] During "normal" operation, ie above a certain minimum speed n min , the speed command variable n lead conventionally corresponds to a speed setpoint n set , which is generated, for example, by a system controller or a simulation.

[0021] At low speeds n, in particular when accelerating from a standstill and decelerating to a standstill, known control methods for load machines in test benches result in losses in terms of control quality. To improve the control quality, according to the invention, the speed reference variable n lead is switched to an adapted speed setpoint n adap using a setpoint switching element 4 that is arranged upstream of the controller 3, when the speed n is below the minimum speed n min. In the case shown, the comparison with the minimum speed n min is made using the speed setpoint n set , but the comparison could also be made, for example, using the speed feedback variable nr. The adapted speed setpoint n adap ensures high and stable control quality even in the slow speed range.The minimum speed n min is selected so that the critical low speed ranges are completely covered and that switching takes place in a speed range that is as uncritical as possible.

[0022] The adapted speed setpoint n adap is formed by an adapter element 5 on the basis of an angle of rotation evaluation, wherein a rotation angle setpoint ϕ set determined by an integrator 6 from the speed setpoint n set is compared with an actual rotation angle value ϕ act determined on the basis of the sensor arrangement 9 (or another corresponding measuring arrangement). With the help of this adapted speed setpoint n adap, the speed reference variable n lead is adjusted in the low speed range depending on how the load machine 2 follows its ideal (angular) position over time. In the case shown, the actual rotation angle value ϕ act is determined from a raw rotation angle signal ϕ raw measured by the sensor arrangement 9, wherein an angle signal conditioning element 7 generates the actual rotation angle value ϕ act from the raw rotation angle signal ϕ raw in a form that matches the rotation angle setpoint ϕ set.

[0023] The use of a position signal (ie angle signal) avoids the problem of the low resolution of the measured speed signal (ie the signal on which the speed feedback variable nr is based) at low speeds n and also has the advantage that at a speed setpoint = 0 rpm the speed cannot drift due to the reference to the absolute value of the angle.

[0024] Fig. 2shows an alternative embodiment of the setpoint switching element 4. Here, the switching of the speed command variable n lead between the speed setpoint n set and the adapted speed setpoint n adap takes place according to a switching characteristic curve 11 which provides a ramp-like transition phase t. Here, too, a minimum speed n min is defined (both for a positive direction of rotation n min +< and for a negative direction of rotation n min -<). For speeds n whose absolute value is above the minimum speed n min, the setpoint switching element 4 again uses the speed setpoint n set as the speed command variable n lead. As soon as the absolute value of the speed falls below the minimum speed n min, the setpoint switching element 4 creates the speed command variable n lead within the transition phase t as a linear combination of the speed setpoint n set and the adapted speed setpoint n adap.If the absolute value of the speed is below the transition phase, the adapted speed setpoint n adap is used as the speed reference variable n lead.

[0025] Fig. 3 shows an advantageous embodiment of a part of the Fig. 1 outlined control, wherein the integrator 6, the angle signal conditioning element 7, and the adapter element 5 are shown in more detail. With reference to Fig. 3 The generation of the adapted speed setpoint n adap will now be explained using this specific embodiment.

[0026] The integrating element 6 generates the angle setpoint ϕ set from the speed setpoint n set as an integrated value normalized to an angular range between 0° and 360°. To enable direct comparison of the actual angle value ϕ act with this value, the raw angle signal ϕ raw is scaled in the angle signal conditioning element 7 (scaling element 12) and also normalized to an angular range between 0° and 360° in a normalizing element 13.

[0027] In the adapter element 5, a rotation angle difference ϕ delta is formed from the rotation angle setpoint ϕ set and the rotation angle actual value ϕ act. The rotation angle difference ϕ delta is normalized in a second normalization element 14 to an angular range between -180° and +180° and amplified in an amplifier element 15. To obtain the adapted speed setpoint n adap, the signal is further subjected to a gradient adjustment 16 and limited by a value limiter 17.

[0028] Fig. 4shows a detailed representation of an actual value switching element 8 according to an alternative embodiment of the invention. Fig. 4 The actual value switching element 8 shown can be used in addition to the control system described above or, if necessary, "standalone," i.e., in conjunction with a conventional control system. The functionality of the actual value switching element 8 is based on the idea of ​​using a high-resolution measurement signal as the speed feedback variable nr at low speeds, which avoids the problems of the measurement signals normally used and originating from low-resolution measuring systems. Nevertheless, the advantages offered by these low-resolution measuring systems should still be usable in higher speed ranges.

[0029] The actual value switching element 8 has two input values, each originating from a measuring device, for example, the sensor arrangement 9, and an output value that is fed back into the control system as a speed feedback variable nr. The first input value is a general speed measurement value nsr, which originates, for example, from a conventional speed measurement device, such as an encoder. The general speed measurement value nsr can, for example, originate from an encoder with a pulse count of 512 and the "1-edge evaluation" acquisition type. At low speeds, the time intervals between the individual measurement points naturally become increasingly larger and can ultimately lead to problems with the control quality. For example, at a speed of 1 rpm (which corresponds to an angle that increases or decreases at 6° / s), such an encoder only generates fewer than 9 pulses per second.If the absolute value of the speed is below a minimum speed n' min, the actual value switching element 8 switches from the general speed measurement value n sr to a high-resolution speed measurement value n hr, which originates from a high-resolution measuring sensor. This is the second input value of the actual value switching element 8.

[0030] The high-resolution speed measurement value n hr can, for example, be obtained from speed measuring systems that already provide a high-resolution signal at a speed of 0 rpm, for example a signal with a frequency of 100 kHz or more. Examples of such high-resolution speed measuring systems include an HMCR16 rotary encoder in conjunction with a HEAG-158 or HMCP 16A signal splitter, both offered by Baumer-Hübner. While such sensors have the advantage of producing a correct measurement value even at very low speeds, they are no longer usable above a certain maximum speed because the values ​​become inaccurate. Switching between the high-resolution speed measurement value n hr and the general speed measurement value n sr occurs in a speed range in which the reliable operating ranges of both sensors overlap, so that when switching at the minimum speed n' min, both values, i.e.the general speed measurement value n sr and the high-resolution speed measurement value n hr match. This avoids jumps in the value of the speed feedback variable nr during switching. Additionally, as already described in connection with setpoint switching element 4, the switching process can be performed with a ramp-like transition phase t', in which the value for the speed feedback variable nr is created as a linear combination of the high-resolution speed measurement value n hr and the general speed measurement value n sr.

[0031] The minimum speed n' min used by the actual value switching element 8 can be the same as the minimum speed n min used by the setpoint switching element 4 (if these two components are used together in a control system), but the values ​​can also differ. In the representation of the figures, the same absolute value is used for the positive minimum speed n min +< or n' min +< and the negative minimum speed n min -< or n' min -<. However, this is not a mandatory requirement and these values ​​can also differ from one another. The ramp-like transitions shown in the figures represent a preferred embodiment due to their simple implementation options; however, it is clear that other types of transitions or switching characteristics can also be used, for example to implement a step-like switchover or a curved switchover without discontinuities, if this is advantageous.

[0032] Fig. 5 shows a control arrangement 1 in which all of the variants described above are implemented together. The sensor arrangement 9 comprises several sensors and generates a general speed measurement value n sr , a high-resolution speed measurement value n hr , and a raw angle signal ϕ raw in order to provide these values ​​to the actual value switching element 8 and the angle signal conditioning element 7, respectively. Variables: Speed ​​n Speed ​​setpoint n set Speed ​​reference variable n lead Adapted speed setpoint n adap Speed ​​feedback variable nr General speed measured value n sr High-resolution speed measured value n hr Minimum speed n min Actual angle of rotation ϕ act Setpoint of rotation ϕ set Raw angle of rotation signal ϕ raw Difference in angle of rotation ϕ delta Reference symbol:Control arrangement 1 Load machine 2 Controller 3 Setpoint switching element 4 Adaptor element 5 Integrating element 6 Angle signal conditioning element 7 Actual value switching element 8 Sensor arrangement 9 Control element 10 Switching characteristic 11, 11' Scaling element 12 Normalizing element 13 Second normalizing element 14 Amplifier element 15 Gradient correction 16 Value limitation 17 Transition phase t, t'

Claims

1. Method for controlling a rotational speed (n) of a load machine (2) on a test bench, the load machine (2) being connected to a test object via a shaft, wherein a rotational speed reference variable (nlead) for a controller (3) is generated from a rotational speed setpoint value (nset), characterized in that an adapted rotational speed setpoint value (nadapt) is determined taking into consideration a rotation angle actual value (ϕact) and a rotation angle setpoint value (ϕset), the rotation angle setpoint value (ϕset) being determined as an integrated value from the rotational speed setpoint value (nset), wherein the rotational speed reference variable (nlead) is switched between the rotational speed setpoint value (nset) and the adapted rotational speed setpoint value (nadapt) as a function of the rotational speed.

2. Method according to claim 1, characterized in that the switching is carried out according to a switching characteristic curve (11) having a preferably ramp-like transition phase (t), the speed reference variable (nlead) in particular corresponding to a linear combination of the rotational speed setpoint value (nset) and the adapted rotational speed setpoint value (nadapt) in the transition phase (t).

3. Method according to either claim 1 or claim 2, characterized in that the adapted rotational speed setpoint value (nadapt) is determined from a deviation of the rotation angle actual value (ϕact) from the rotation angle setpoint value (ϕset).

4. Method according to any of claims 1 to 2, characterized in that the rotation angle setpoint value (ϕset) is determined as a normalized value from the rotational speed setpoint value (nset).

5. Method according to any of claims 1 to 4, characterized in that the rotation angle actual value (ϕact) is determined a as scaled and normalized value from a rotation angle raw signal (ϕraw).

6. Method according to any of claims 1 to 5, characterized in that a rotational speed feedback variable (nr) of the control system is switched between a general rotational speed measurement value (nsr) and a high-resolution rotational speed measurement value (nhr) as a function of the rotational speed.

7. Method according to claim 6, characterized in that the switching is carried out according to a switching characteristic curve (11') having a preferably ramp-like transition phase (t'), the rotational speed feedback variable (nr) in particular corresponding to a linear combination of the general rotational speed measurement value (nsr) and the high-resolution rotational speed measurement value (nhr) in the transition phase (t').

8. Control arrangement (1) for controlling the rotational speed (n) of a load machine (2) on a test bench, the load machine (2) being connected to a test object via a shaft, characterized in that the control arrangement (1) has an integrating element (6) which determines a rotation angle setpoint value (ϕset) from a rotational speed setpoint value (nset), an adapting element (5) which, taking into consideration a rotation angle actual value (ϕact) and the rotation angle setpoint value (ϕset), determines an adapted rotational speed setpoint value (nadapt), and a setpoint value switching element (4) which switches a rotational speed reference variable (nlead) between the rotational speed setpoint value (nset) and the adapted rotational speed setpoint value (nadapt) as a function of the rotational speed.

9. Control arrangement (1) according to claim 8, characterized in that the setpoint value switching element (4) is designed to carry out the switching process according to a switching characteristic curve 11 having a preferably ramp-like transition phase (t), in which the rotational speed reference variable (nlead) is in particular determined as a linear combination of the rotational speed setpoint value (nset) and the adapted rotational speed setpoint value (nadapt).

10. Control arrangement (1) according to either claim 8 or claim 9, characterized in that the control arrangement (1) has an adapting element (5) which determines the adapted rotational speed setpoint value (nadapt) from a deviation of the rotation angle actual value (ϕact) from a rotation angle setpoint value (ϕset).

11. Control arrangement (1) according to any of claims 8 to 10, characterized in that the control arrangement (1) has an integrating element (6) which determines the rotation angle setpoint value (ϕset) as an integrated and normalized value from the rotational speed setpoint value (nset).

12. Control arrangement (1) according to any of claims 8 to 11, characterized in that the control arrangement (1) has an angle signal processing element (7) which determines the rotation angle actual value (ϕact) as a scaled and normalized value from a rotation angle raw signal (ϕraw).

13. Control arrangement (1) according to any of claims 8 to 12, characterized in that the control arrangement (1) has an actual value switching element (8) which switches a rotational speed feedback variable (nr) of the control system between a general rotational speed measurement value (nsr) and a high-resolution rotational speed measurement value (nhr) as a function of the rotational speed.

14. Control arrangement according to claim 13, characterized in that the actual value switching element (8) is designed to carry out the switching process according to a switching characteristic curve (11') having a preferably ramp-like transition phase (t'), in which the rotational speed feedback variable (nr) is in particular determined as a linear combination of the general rotational speed measurement value (nsr) and the high-resolution rotational speed measurement value (nhr).