Controlled stopping method for a textile machine and textile machine stopped by this process

Abstract

A method and a device for bringing a textile machine to a controlled standstill in the event of a failure of the power supply, and a correspondingly equipped textile machine, the textile machine having at least two axes that are driven in synchronization by respective electric motors (M1-M.sub.5) connected to a common intermediate voltage circuit (1), and in which at least one electric motor acting as power generator can supply electric power to at least one other electric motor via the common DC bus (1), and in which the voltage (V) on the common DC bus is controlled by varying at least two variables in such a way that the voltage follows a previously defined curve while the textile machine is being brought to a standstill.

Claims

1. A method for bringing a textile machine to a controlled standstill in a condition without power supply or with reduced or disturbed power supply, the textile machine having at least two axes provided to be driven in synchronization by respective separately controlled electric motors connected to a common intermediate voltage circuit (common DC bus), and in which at least one electric motor acting as power generator can supply electric power to at least one other electric motor via the common DC bus, comprising controlling the voltage on the common DC bus by varying at least two variables in such a way that the value of the voltage follows a previously defined curve while the textile machine is being brought to a standstill, wherein the voltage on the common DC bus is controlled by a cascade control, and wherein the cascade control comprises: a relatively slow control loop repeatedly or continuously determining a voltage difference, being the difference between a measured instantaneous value of the voltage on the common DC bus and the desired value at that moment of the voltage corresponding to the previously determined curve of the voltage, varying the voltage on the common DC bus in such a way that the voltage difference is reduced, and determining the energy flow required to bring the voltage difference to zero.

2. The method according to claim 1, characterized in that at least one of said variables is a motor parameter of one or more electric motors.

3. The method according to claim 1, characterized in that one or more main axes are selected that have a higher energy content during normal operation of the textile machine than the other axes of the textile machine, and that at least one motor parameter of only one or more electric motors driving a main axis of the textile machine is varied.

4. The method according to claim 1, characterized in that the textile machine is a machine for the manufacture of a product made from textile material, comprising one or more pattern-forming elements controllable by means of electric controllers, and that at least part of said controllers of the pattern-forming elements is connected to the common DC bus.

5. The method according to claim 4, characterized in that the pattern-forming elements are controlled in such a way during the period the textile machine comes to a standstill that they remain in operation forming the pattern until the textile machine has come to a complete standstill, as with a controlled switching-off of the textile machine.

6. The method according to claim 1, characterized in that the cascade control further comprises: a relatively fast control loop repeatedly or continuously calculating the actual value of the energy flow supplied by the axis from the measured value of the speed of at least one axis and from one or more motor parameters of an electric motor driving the axis, and varying one or more motor parameters of at least one electric motor driving an axis in such a way that a determined difference between the required energy flow and the calculated value of the energy flow supplied by the axis is reduced.

7. The method according to claim 6, characterized in that the cascade control entails calculating a first value of one or more parameters that are proportional to the energy flow that is proportional to the desired energy flow, and calculating a second value that is proportional to the actual energy flow, and with the relatively fast control loop, varying said one or more motor parameters in such a way that a difference determined between the first and the second value of one or more parameters is reduced.

8. The method according to claim 1, characterized in that one or more of the following motor parameters are varied to control the voltage on the common DC bus: motor current, motor voltage, motor flux and motor torque.

9. A control device for bringing a textile machine to a controlled standstill in a condition without power supply or with reduced or disturbed power supply, the textile machine having at least two axes provided to be driven in synchronization by respective separately controlled electric motors connected to a common intermediate voltage circuit (common DC bus), and in which at least one electric motor acting as power generator can supply electric power to at least one other electric motor via the common DC bus, wherein the control device is provided to control the voltage on the common DC bus by varying at least two variables in such a way that the value of this voltage follows a previously defined curve while the textile machine is being brought to a standstill, wherein the control device comprises a cascade control for controlling the voltage on the common DC bus, and wherein the cascade control comprises: a relatively slow control loop repeatedly or continuously determining a voltage difference, being the difference between a measured instantaneous value of the voltage on the common DC bus and the desired value at that moment of the voltage corresponding to the previously determined curve of the voltage, varying the voltage on the common DC bus in such a way that the voltage difference is reduced, and determining the energy flow required to bring the voltage difference to zero.

10. The control device according to claim 9, characterized in that at least one of said variables is a motor parameter of one or more electric motors.

11. The control device according to claim 9, characterized in that the cascade control comprises: a relatively fast control loop provided to repeatedly or continuously calculate the actual value of the energy flow supplied by the axis from the measured value of the speed of at least one axis with a relatively large energy content, and from one or more motor parameters of an electric motor driving the axis, and vary one or more motor parameters of at least one electric motor driving an axis in such a way that a determined difference between the required energy flow and the calculated value of the energy flow is reduced.

12. The control device according to claim 11, characterized in that the cascade control is provided to calculate a first value that is proportional to the desired energy flow from one or more parameters that are proportional to the energy flow, and to calculate a second value that is proportional to the actual energy flow, and, with the relatively fast control loop, to vary said one or more motor parameters in such a way that a difference determined between the first and the second value of one or more parameters is reduced.

13. The control device according to claim 9, characterized in that it is provided for bringing a textile machine to a controlled standstill in a condition without power supply or with reduced or disturbed power supply by controlling the voltage on the common DC bus by varying at least two variables in such a way that the value of the voltage follows a previously defined curve while the textile machine is being brought to a standstill.

14. A textile machine comprising at least two axes provided to be driven in synchronization by respective separately controlled electric motors connected to a common intermediate voltage circuit (common DC bus), in which at least one electric motor acting as power generator can supply electric power to at least one other electric motor via the common DC bus, and a control device for bringing said axes to a controlled standstill in a condition without power supply or with reduced or disturbed power supply, wherein the textile machine comprises a control device according to claim 9.

15. The textile machine according to claim 14, characterized in that it comprises one or more main axes that have a higher energy content during normal operation of the textile machine than the other axes of the textile machine, and that the control device is provided only to vary at least one motor parameter of one or more electric motors driving a main axis of the textile machine.

16. The textile machine according to claim 14, characterized in that it is a machine for the manufacture of a product made from textile material, comprising one or more pattern-forming elements controllable by means of electric controllers, and that at least part of said controllers of the pattern-forming elements is connected to the common DC bus.

17. The textile machine according to claim 16, characterized in that it comprises a control device provided to control the pattern-forming elements in such a way during the period the textile machine comes to a standstill that the pattern-forming elements remain in operation forming the pattern until the textile machine has come to a complete standstill, as with a controlled switching-off of the textile machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to further illustrate the characteristics of the invention, a detailed description is given below of a possible control device according to this invention. It should be clear that this is only one example of the many possible embodiments covered by the invention, and that this description can in no way be regarded as a limitation of the scope of the protection. In this detailed description, reference numbers are used to refer to the attached figures, wherein

(2) FIG. 1 is a schematic representation of the various electric motors of a textile machine according to an embodiment of this invention connected to a common DC bus;

(3) FIG. 2 is a schematic representation of a control device for bringing a textile machine to a controlled standstill according to an embodiment of this invention;

(4) FIG. 3 is a schematic representation of the cascade controller of the control device according to FIG. 2;

(5) FIG. 4 shows a stepwise declining curve of the voltage on the common DC bus, and

(6) FIG. 5 shows a continuously declining curve of the voltage on the common DC bus.

DETAILED DESCRIPTION OF EMBODIMENTS

(7) A textile machine according to this invention in the embodiment shown schematically in FIG. 1 has five axes driven by respective electric motors (M.sub.1, M.sub.2, M.sub.3, M.sub.4, M.sub.5). Each axis has its own inertia (J.sub.1, J.sub.2, J.sub.3, J.sub.4, J.sub.5). The electric motors are controlled by separate motor controllers (I.sub.1), (I.sub.2), (I.sub.3), (I.sub.4), (I.sub.5) and are connected to a common intermediate voltage circuit (1) or common DC bus. Under normal operating conditions, they are supplied with electric power from the mains via an AC/DC converter (2) and a switching device (3).

(8) The axis driven by the left-hand motor (M.sub.1) is the axis with the highest energy content or the energy-dominant axis. On a weaving machine this is the main axis.

(9) The word axis is used to mean not only the axis itself, but also all the parts set in motion by this axis. Energy content means the kinetic energy that with a rotational motion is a function of the inertia (J.sub.1) and the angular velocity () of the axis according to the following formula:
Kinetic energy=.Math.J.sub.1.Math..sup.2

(10) When a failure of the power supply or a reduction or fault in the power supply is detected by means of detection means (not shown in the figure), a control device with a cascade controller is automatically activated which ensures that the kinetic energy present in the energy-dominant axis is reduced in a controlled manner. In the process, the kinetic energy is converted by the electric motor (M.sub.1) acting as a generator into electrical energy that is supplied via the common DC bus (1) to the other electric motors (M.sub.2, M.sub.3, M.sub.4, M.sub.5) connected to the common DC bus (1). The supply of energy by the electric motor (M.sub.1) is indicated symbolically in FIG. 1 by means of an arrow pointing upwards. The consumption of energy by the other electric motors (M.sub.2, M.sub.3, M.sub.4, M.sub.5) is indicated symbolically by means of arrows pointing downwards. The cascade controller (20),(21) is described in further detail by reference to FIGS. 2 and 3.

(11) Via the cascade controller (20), (21), the available energy is reduced in such a way that the returning energy flow is high enough to supply the separately driven motors with energy and to enable these to bring the associated actuators to a sufficiently safe position and to block them there. On servo-controlled weaving frames, for example, this is a top dead centre or bottom dead centre position so that rapier movements can no longer cause damage due to an incorrect position of the weaving frames. For rapiers this is a position outside the shed forming zone.

(12) FIG. 2 shows a schematic representation of a possible embodiment of the control system for the energy-dominant axis with inertia (J.sub.1) that is driven by motor (M.sub.1). In variant embodiments, the location and the arrangement of the controllers differ.

(13) The motor controller (6) ensures the pure hardware transformation of the desired motor behaviour by controlling the motor currents. This motor controller (6) is provided at the input with a switch (7) that can be either mechanical or electronic or purely in the form of software.

(14) The device also comprises a speed controller (8) that bases its control on the measured value (v) of the instantaneous speed and a certain target value or a desired speed (v.sub.des). In a normal operating situation, the output signal (9) from this speed controller current (8) is transmitted to a torque or frequency controller (10) to determine the optimum motor current.

(15) The output (11) from the torque or frequency controller (10) is connected via the switch (7) to the motor controller (6) which controls the motor (M.sub.1) directly on the basis of the specific desired motor current.

(16) The device also comprises detection means for detecting the failure of the power supply. These detection means (not shown in the figure) are provided to transmit a detection signal to the switch so that this switch (7) can be switched from the position indicated by the solid line in which the motor controller (6) is connected to the output of the combination of speed controller (8) and torque or frequency controller (10) to the position indicated by the dotted line in which the motor controller (6) is connected to the output of the cascade controller (20), (21).

(17) After detection of the failure of the power supply (mains failure or mains drop) or after detection of a reduced or disturbed power supply, the normal speed control (8), (10) with this/these motor controller(s) is thus replaced by a special cascade controller (20), (21) with a slow and a fast control loop with the goal of making efficient use of the kinetic energy present in the global system as much as possible (energy harvesting) so that both the main system with the energy-dominant axis driven by the electric motor (M.sub.1) and all the sub-systems with the respective axes driven by the other electric motors (M.sub.2-M.sub.5) connected to the intermediate voltage circuit (common DC bus) can be brought to a standstill in a safe manner.

(18) According to some embodiments of the invention, the voltage (V) on the common DC bus (1) is allowed to follow the most favourable possible curve instead of allowing the speed of the energy-dominant axis to follow an imposed deceleration profile.

(19) Depending on the known characteristics, the conditions, the desired result, etc., the values for a number of parameters of the dominant axis can be used in the faster cascade control loop (21) to compensate the fault in the voltage (V) of the common DC bus (1) as well as possible.

(20) In addition to the measured value (v) for the speed, this cascade controller (20),(21) also uses a number of other measured parameters (30), including the motor current, motor voltage, etc., and parameters (30) calculated on the basis of a motor model from the measured parameters (30), such as the motor flux.

(21) FIG. 3 is an illustration of a possible implementation of the cascade controller (20), (21) in which the motor controller (6) is connected to the output of the cascade controller (20), (21); this represents the situation after detection of a failure of the power supply (mains failure or mains drop) or after detection of a reduced or disturbed power supply. This cascade controller consists of a slower common DC bus controller (20) and a faster internal controller (21).

(22) The slower common DC bus controller (20) comprises a comparator (20a) and a control section (20b). In the first instance, the slower common DC bus controller (20) controls the voltage (V) to the desired voltage level. For this, the voltage difference (V) is continuously determined in the comparator (20a) between the measured actual value (V.sub.m) of the voltage (V) on the common DC bus (1) and the desired value (V.sub.des) at that moment of the voltage (V) corresponding to the previously determined curve of the voltage (V). Examples of this imposed voltage curve are shown in FIGS. 4 and 5.

(23) The control section (20b) of the slower common DC bus controller (20) continuously varies the voltage (V) of the common DC bus with the goal of reducing the determined voltage difference (V).

(24) The output signal from the control section (20b) is a parameter (it can also be several parameters) that is proportional to the difference between the desired DC bus voltage (V.sub.des) and the actual measured DC bus voltage (V.sub.m), such as this voltage difference itself or other values calculated from this. This voltage difference or this calculated value is in any case representative of the energy flow (E.sub.des) required (hereinafter referred to as the required energy flow) to reduce the determined voltage difference (V)i.e. the measuring error of the slow controller (20)to zero, and this is used as input signal for the faster controller (21).

(25) The faster controller (21) comprises a comparator (21a), a control section (21b), a first computation module (21c) provided to calculate certain other parameters from measured parameters on the basis of a motor model, and a second computation module (21d).

(26) In the first computation module (21c), a number of other parameters (30) are calculated from the measured values (v) of the instantaneous speed and from other measured parameters (30) on the basis of the motor model, and from these measured (v) and calculated parameters (30) the value of a parameter representative of the actual value (E.sub.act) of the energy flow supplied by the dominant axis is calculated in the second computation module (21d).

(27) If a difference (E) is determined between the required energy flow (E.sub.des) and the calculated value of the energy flow (E.sub.act) supplied by the energy-dominant axis, the faster controller (21) will vary one or more motor parameters (I.sub.mot, V.sub.mot, .sub.mot, T.sub.mot) of the electric motor (M.sub.1) driving the energy-dominant axis with the goal of reducing this determined difference (E) to zero.

(28) The control error (V) of the slow controller (20) is therefore used as an input in order to control one or more parameters of the electric motor (M.sub.1) driving the energy-dominant axis taking this control error into account in such a way that this error is minimized and the harvested energy is maximized.

(29) Internally in the cascade controller (20), (21), the slow controller (20) continuously adapts the target value of the selected control parameter E.sub.des so that the voltage (V) on the common DC bus follows the previously determined curve.

(30) If the instantaneous voltage (V.sub.m) on the common DC bus is lower than the desired value (V.sub.des) for that voltage, energy has to be harvested. The electric motor (M.sub.1) of the energy-dominant axis then has to act as a generator (operate in generator mode), whereby kinetic energy is being converted into electrical energy that is supplied via the common DC bus to the connected electric motors of the whole system. As a result, the instantaneous voltage (V.sub.m) increases.

(31) If the instantaneous voltage (V.sub.m) is higher than the desired value (V.sub.des) of that voltage, the energy-dominant axis can run in production mode. In production mode, the electric motor has a predominantly motoring or driving behaviour. In order to not have to provide undesirable and otherwise useless energy-dissipating components (in the form of brakes, resistance elements, etc.), the energy-dominant axis can at that moment increase its speed so that the excess kinetic energy is not lost and the whole system has sufficient energy available over a prolonged period.

(32) For this control device, the cascade control is of particular importance, particularly the interaction between on the one hand the internal faster controller (21) that both compensates instantaneous variations in speed and friction of the energy-dominant axis and at the same time cushions the drop in energy as a result of the decreasing machine speed, and on the other hand the slower common DC bus controller (20) that compensates the instantaneous voltage variations as a result of the drives connected to the common DC bus (1).

(33) As a result of this cascade control with a high closed-loop bandwidth thanks to the internal faster controller (21), the mechanical properties of the energy-dominant axis (its inertia and friction) have practically no influence on the effectiveness of the voltage control.

(34) In order to make the maximum energy content of the main axis available to all the motors, the final voltage of the common DC bus must be reduced as far as possible. In other words, the energy content present in the textile machine must be used up as much as possible.

(35) Initially the target value of the voltage on the common DC bus at the moment of failure of the power supply is equal to the maximum permissible value. Alternatively, the value of the voltage on the common DC bus at the moment of failure of the power supply can also be taken as the target value.

(36) The imposed voltage on the common DC bus can be constant, for example the maximum permitted voltage on the common DC bus or the voltage on the common DC bus at the moment of failure of the power supply. The imposed voltage can also be variable.

(37) Examples of the curve of the voltage on the common DC bus imposed by the control device according to some embodiments of this invention are: a constant higher value (voltage boost) relative to the initial value immediately after the failure of the power supply; and a constant lower value relative to the initial value immediately after the failure of the power supply; and a varying value, decreasing as a function of the decreasing speed of the movements in order to be able to use the regenerated energy for as long as possible.

(38) The controller can be coupled to one single motor controller, preferably the motor controller of the motor with the highest kinetic energy, or to several motor controllers if there are several energy-dominant axes.

(39) FIG. 4 illustrates a possible imposed curve of the voltage (V) on the common DC bus as a function of time (t), where the target value of the voltage decreases stepwise and successively takes on the following constant values: V.sub.dc,1: the target value with power failure at time t.sub.1 V.sub.dc,2: the reduced target value from time t.sub.2 V.sub.dc,3: the further reduced target value from time t.sub.3, and V.sub.dc,4: the lowest target value from time t.sub.4.

(40) These values for the voltage on the common DC bus ensure a sufficiently high speed of the connected axes and also guarantee the minimum required operating voltage for the servo-controlled axes (e.g. 250 to 300 volt DC).

(41) From time t.sub.4, the desired common DC bus voltage must remain constant in order to maintain a good function of the system.

(42) Instead of a stepwise reduction in the target value of the common DC bus controller, a voltage curve following a continuously varying function can be imposed. This type of curve is shown in FIG. 5. This function is determined, taking into consideration the dynamic behaviour of the connected primary and secondary axes.

(43) In one variant of this, this function can also be determined by the moment of the failure of the power supply, taking into consideration the position and corresponding energy behaviour of the connected axes at that moment in time.