Laboratory apparatus having a movable element and a drive device

Abstract

A laboratory apparatus (100) comprises a movable element (10) and a drive device (50) for moving the movable element (10). The drive device (50) includes a stepper motor (20) and a control unit (30) for controlling the stepper motor (20). The control unit (30) is designed to control the stepper motor (20) by way of field-oriented control.

Description

[0001] Laboratory device with a movable element and a drive device

[0002] The present invention relates to a laboratory device with a movable element and a drive device for the same.

[0003] Laboratory equipment is used in laboratory operations, for example, in the fields of physics, chemistry, biology, and pharmacy. Some of these laboratory devices have movable elements through which substances are conveyed or mixed, for example. These include peristaltic pumps, shaker-mixers, laboratory stirrers, and rotary evaporators.

[0004] Such a movable element is usually driven by a DC motor or a shaded-pole motor. However, these motor types only deliver low torque at low speeds. To achieve the torque required for operation in laboratory equipment, such a motor is operated at a high speed, which is then reduced to the required speed via a gearbox (a reduction gear). Such a drive is complex and contains many parts. On the other hand, designing such a motor for high torque at low speeds would require large dimensions, making it unsuitable for use in many laboratory equipment.

[0005] The object of the present invention is to provide a drive device for a laboratory device and a laboratory device with this drive device, which are simplified compared to the conventional drive and contain fewer parts.

[0006] This object is achieved by a laboratory device according to claim 1. Further developments of the invention are specified in the subclaims.

[0007] The laboratory device according to the invention contains a movable element and a drive device for moving the movable element. The drive device contains a stepper motor and a control unit for controlling the stepper motor. The control unit is designed to control the stepper motor using a field-oriented control system.

[0008] Field-oriented control (FOC), also known as vector control, is a control method that aims to align the excitation flux and the armature magnetomotive force of a motor as perpendicular to each other as possible. This makes it possible to achieve the motor's maximum torque. For this purpose, a feedback control loop is provided in which data acquired from the machine is processed via transformations.

[0009] Implementing the drive device with a stepper motor and controlling the stepper motor using field-oriented control makes it possible, for example, to simplify the structure of the laboratory device and reduce the number of parts it contains. This can lead to simplified production of the laboratory device and lower manufacturing costs.

[0010] Preferably, the movable element is connected to the stepper motor without a gear. This allows, for example, a further reduction in the number of parts, further simplifies manufacturing, and further reduces manufacturing costs.

[0011] Preferably, the movable element is connected to a rotor of the stepper motor via a shaft. The movable element can also be formed by a shaft or contain a shaft, be drivingly connected to the output shaft of the stepper motor, or be formed integrally with it. This allows, for example, a particularly simple method of connecting the movable element to the stepper motor.

[0012] Preferably, the field-oriented control is designed so that the speeds and / or torques required to drive the movable element are generated directly by the stepper motor. "Control design" refers to the dimensioning of the individual function blocks contained in a control loop used to implement the control. In other words, the control design includes a suitable selection of the transfer function parameters of these function blocks. Such a control design can be used, for example, to enable a gearless connection between the movable element and the stepper motor.

[0013] Preferably, the drive device further includes a two-phase inverter for generating a two-phase AC voltage from an input DC voltage, wherein the output of the two-phase inverter is connected to the stepper motor via two motor leads. By driving the stepper motor with a sinusoidal AC voltage, it is possible, for example, to avoid step losses of the stepper motor and reduce running noise.

[0014] Preferably, the stepper motor includes an encoder for outputting an encoder signal containing information about the position of the rotor in the stepper motor. This makes it possible, for example, to perform field-oriented control of the stepper motor depending on the current rotor position.

[0015] Preferably, the control unit contains a position and speed determination unit for determining a rotor angle, an actual position, and an actual speed from the encoder signal output by the encoder and from current measurement signals that reflect the currents flowing in the two motor leads. This makes it possible, for example, to provide the actual variables of the stepper motor operation required for field-oriented control.

[0016] Preferably, the control unit further includes a first controller, preferably a PI controller, for generating a target speed from a deviation between a predetermined target position and the actual position, a second controller, preferably a PI controller, for generating a target control signal from a deviation between the target speed and the actual speed, a first transformation unit for performing a Park transformation to generate a first control signal and a second control signal from the current measurement signals and the rotor angle, a third controller, preferably a PI controller, for generating a third control signal from a deviation between the target control signal and the first control signal, a fourth controller, preferably a PI controller,for generating a fourth control signal from the second control signal and a second transformation unit for performing an inverse Park transformation to generate voltage control signals from the third control signal, the fourth control signal and the rotor angle, wherein the voltage control signals are applied to the two-phase inverter to control the generation of the two-phase AC voltage.

[0017] This selection of individual function blocks and their arrangement in a control loop makes it possible, for example, to provide a concrete structure for the field-oriented control of the stepper motor.

[0018] Preferably, the control unit further includes a maximum torque determination unit for calculating a maximum torque, wherein the second controller is configured to generate the target control signal taking into account the maximum torque calculated by the maximum torque determination unit. This makes it possible, for example, to prevent the control loop from becoming unstable at higher speeds.

[0019] Preferably, the control unit further includes a torque current determination unit for calculating a value of the first control signal required to achieve a predetermined torque, and a torque current limiting unit for limiting the value of the first control signal calculated by the torque current determination unit. This makes it possible, for example, to prevent an overcurrent and any resulting overheating or damage to the motor.

[0020] Preferably, the control unit further includes a decoupling network for decoupling the control of the first control signal and the second control signal. This makes it possible, for example, to control the magnetic flux and the torque of the motor separately, thereby achieving improved motor dynamics.

[0021] Preferably, the laboratory device is a laboratory stirrer, a peristaltic pump, a rotary evaporator, or a shaker-mixer. This makes it possible, for example, to apply the effects of the invention to the respective types of laboratory devices.

[0022] A method according to the invention for controlling a movable element in a laboratory device comprises connecting the movable element to a stepper motor and controlling the stepper motor by means of a field-oriented control.

[0023] The field-oriented control is preferably designed so that the speeds and / or torques required to drive the movable element are generated directly by the stepper motor.

[0024] With such a method and its further developments described below, for example, the same effects can be achieved as with the laboratory device according to the invention.

[0025] Preferably, the method according to the invention further comprises generating a two-phase alternating voltage by means of a two-phase inverter from an input direct voltage and applying the two-phase alternating voltage as operating voltage to the stepper motor, outputting an encoder signal containing information about a position of the rotor in the stepper motor by means of a decoder contained in the stepper motor, determining a rotor angle, an actual position and an actual speed from the encoder signal output by the encoder and from current measurement signals that reflect the currents flowing in the two motor leads by means of a position and speed determination unit, generating a target speed from a deviation between a predetermined target position and the actual position by means of a first controller,generating a target control signal from a deviation between the target speed and the actual speed using a third controller; performing a Park transformation to generate a first control signal and a second control signal from the current measurement signals and the rotor angle using a first transformation unit; generating a third control signal from a deviation between the target control signal and the first control signal using a third controller; generating a fourth control signal from the second control signal using a fourth controller; performing an inverse Park transformation to generate voltage control signals from the third control signal, the fourth control signal, and the rotor angle using a second transformation unit; and applying the voltage control signals to the two-phase inverter to control the generation of the two-phase AC voltage.

[0026] Further features and advantages of the invention will become apparent from the description of embodiments with reference to the accompanying drawings.

[0027] Fig. 1 is a schematic diagram of a laboratory device according to a first embodiment of the present invention.

[0028] Fig. 2a is a schematic block diagram of a drive device included in the laboratory device shown in Fig. 1.

[0029] Fig. 2b is a schematic block diagram of a modification of the drive device shown in Fig. 2a.

[0030] Fig. 3 is a schematic diagram of a laboratory device according to a second embodiment of the present invention.

[0031] Fig. 4 is a schematic diagram of a laboratory device according to a third embodiment of the present invention.

[0032] Fig. 5 is a schematic diagram of a laboratory device according to a fourth embodiment of the present invention. Embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a schematic diagram of a laboratory device 100 according to a first embodiment.

[0033] According to the present embodiment, the laboratory device 100 is designed as a laboratory stirrer. The movable element is formed by a stirring rod 10. The stirring rod 10 comprises a stirring head 11 and a shaft 12 connected thereto. The stirring rod can be used to stir substances in a vessel (not shown) into which the stirring head is immersed.

[0034] A stepper motor 20 is provided to drive the stirring rod 10. During operation of the laboratory device, the stepper motor 20 rotates the stirring head 11 via the shaft 12. The stepper motor 20 contains a stator 21 and a rotor 22. The stirring head 11 is connected to the rotor 22 of the stepper motor via the shaft 12.

[0035] Furthermore, a control unit 30 is provided, which is designed to control the stepper motor 20. The stepper motor 20 and the control unit 30 together form a drive device 50 for the stirring rod 10. To supply the stepper motor 20 and the control unit 30, the laboratory device 100 further includes a power supply 40, for example, a wide-range power supply, for generating internal supply voltages from an externally supplied mains voltage.

[0036] The control unit 30 is designed to control the stepper motor 20 using a field-oriented control. Fig. 2a is a schematic block diagram of the drive device 50, which serves to explain this field-oriented control.

[0037] The stepper motor 20 contains an encoder 23 which outputs an encoder signal E containing information about a position of the rotor 22 in the stepper motor 20.

[0038] The control unit 30 contains a two-phase inverter 31 that generates a two-phase alternating voltage VAC from a direct voltage VDC provided by the power supply 40. The output of the two-phase inverter is connected to the stepper motor 20 via two motor leads 31a, 31b. The alternating voltage VAC is applied as the operating voltage to the stator 21 of the stepper motor 20 via the motor leads 31a, 31b.

[0039] The control unit 30 further includes a first transformation unit 32 and a position and speed determination unit 34. The currents flowing in the motor supply lines 31a, 31b are detected via current sensors (not shown) and fed as current measurement signals Ia and Iß to the first transformation unit 32 and the position and speed determination unit 34.

[0040] The position and speed determination unit 34 determines a rotor angle cp, an actual position P and an actual speed n from the encoder signal E output by the encoder 23 and the current measurement signals Ia and Iß. The rotor angle <p eine Winkelstellung des Rotors 22 innerhalb des Schrittmotors in einem Bereich von 0° bis 360°. Die Istposition dagegen zählt den Winkel fortlaufend weiter und erreicht somit bei mehrfacher Drehung des Rotors ein Mehrfaches von 360°.

[0041] A first controller 35, which is preferably designed as a PI controller, generates a target speed nz from a deviation between a predetermined target position Pz and the actual position P. A second controller 36, which is preferably designed as a PI controller, generates a target control signal Iqz from a deviation between the target speed nz and the actual speed n.

[0042] The first transformation unit 32 performs a Park transformation and generates a first control signal Iq and a second control signal Id from the current measurement signals Ia and Iß and the rotor angle ωp in a two-axis coordinate system with axes d and q, which rotates with the rotor, so that Iq and Id represent temporally constant quantities in the stationary case. Id represents the magnetic flux density of the magnetic excitation in the rotor, and Iq is an expression for the torque generated by the rotor. Temporal changes in the speed or torque result in temporal changes in Id or Iq, respectively. A third controller 37, which is preferably designed as a PI controller, generates a third control signal Vq from a deviation between the target control signal Iqz and the first control signal Iq. A fourth controller 38, which is preferably designed as a PI controller, generates a fourth control signal Vd from the second control signal Id.

[0043] A second transformation unit 33 performs an inverse Park transformation and generates from the third control signal Vq, the fourth control signal Vd and the rotor angle <p die Spannungssteuersignale Va und Vß. Die Spannungssteuersignale Va und Vß werden an den zweiphasigen Wechselrichter 31 angelegt und steuern die Erzeugung der zweiphasigen Wechselspannung VAC.

[0044] The individual function blocks of this control loop are dimensioned in such a way, ie the parameters of the transfer functions of these function blocks are selected in such a way that the stepper motor 20 directly generates the speed and torque required to drive the movable element 10.

[0045] This allows the movable element to be firmly connected to the stepper motor without any type of gearing in between. Compared to conventional drive devices, the structure is simplified and the number of parts is reduced. This can also reduce manufacturing costs, for example.

[0046] Even if a gearbox is provided between the motor and the moving element, it can be dimensioned for a much lower reduction ratio, thus still simplifying the design and reducing manufacturing costs. For example, a 1:1 gearbox can also be used.

[0047] Since the field-oriented control operates with a sinusoidal alternating voltage and not with steps like conventional stepper motor control, step loss is also eliminated. Furthermore, the running noise associated with conventional stepper motor control, which is highly disruptive in many laboratory environments, is eliminated. This control allows full torque to be accessed even at the lowest speeds. By dimensioning the successive function blocks of the control loop, the positions of the moving element in the laboratory device can be precisely approached and maintained.

[0048] These properties make the field-oriented controlled stepper motor a suitable drive for all types of laboratory equipment that has a movable element.

[0049] Fig. 2b is a schematic block diagram of a drive device 50', which is a modification of the drive device 50 shown in Fig. 2a. Like elements are provided with like reference numerals and will not be explained again in the following description.

[0050] In addition to the elements of the drive device 50, the drive device 50' includes a torque maximum determination unit 80, a torque current determination unit 81, a torque current limiting unit 82, a reference signal generation unit 83 and a decoupling network 84.

[0051] The maximum torque determination unit 80 receives the first control signal Iq and the second control signal Id and calculates the maximum torque Mmax that can be applied at a specific operating point. The second controller 36 takes into account the maximum torque Mmax calculated by the maximum torque determination unit 80.

[0052] The torque current determination unit 81 receives the output signal of the second controller 36 and calculates a corresponding value of Iq required for a specific motor torque. The torque current limiting unit 82 receives the output signal of the torque current determination unit 81 and limits the value of Iq so that the condition Iq 2 + ID 2 < Imax 2 is fulfilled, whereby

[0053] Imax is a maximum current. The output signal of the torque current limiting unit 82 is a first reference signal Iqref (a reference signal for the first control signal Iq). The third controller 37 is supplied with a difference signal from the first reference signal Iqref and the first control signal Iq.

[0054] The reference signal generation unit 83 generates a second reference signal Idref (a reference signal for the second control signal Id). A differential signal from the second reference signal Idref and the second control signal Id is supplied to the fourth controller 38.

[0055] The decoupling network 84 receives the first control signal Iq and the second control signal Id and is configured to decouple the control of the two components Iq and Id, and thus the magnetic flux and torque of the motor 20, from each other. The decoupling network 84 outputs a fifth control signal Vq_FF and a sixth control signal Vd_FF. The suffixes FF denote the fact that the fifth and sixth control signals are output by the decoupling network 84 in a feedforward manner.

[0056] The second transformation unit 33 is supplied with a first sum signal Vqsum from the third control signal Vq and the fifth control signal Vq_FF and a second sum signal Vdsum from the fourth control signal Vd and the sixth control signal Vd_FF.

[0057] Otherwise, the operation of all components is the same as described above for the drive device 50 and will not be described again here.

[0058] Using drive device 50', the same effects can be achieved as with drive device 50. In addition, by calculating the maximum torque Mmax and incorporating it into the control system, the control loop can be prevented from becoming unstable at higher speeds. Furthermore, current limitation by means of torque current determination unit 81 and torque current limiting unit 82 can prevent overcurrent and any resulting overheating or damage to the motor.

[0059] Furthermore, improved motor dynamics can be achieved by decoupling the two components Iq and Id using the decoupling network 84. This block can also predict an expected open-circuit voltage to compensate for it.

[0060] Fig. 3 is a schematic representation of a laboratory device 200 according to a second embodiment. The laboratory device 200 according to this embodiment is designed as a peristaltic pump (hose pump). The movable element is formed by a wheel 10a, to which rollers 13 are attached on both sides. The wheel 10a is connected to the rotor of the stepper motor 20 via a shaft 12a.

[0061] During operation of the peristaltic pump, a tube 14 is pressed against a housing wall 15 by the rollers 13, thus clamping it at these points. A medium contained in the tube between the clamped points is conveyed further within the tube 14 by the rotation of the wheel 10a.

[0062] To drive the wheel 10a, the laboratory device 200 includes the drive device 50 containing the stepper motor 20 and the control unit 30, and the power supply 40, as described in the first embodiment. Thus, the advantageous effects of the first embodiment can also be achieved with a peristaltic pump.

[0063] Fig. 4 is a schematic representation of a laboratory device 300 according to a third embodiment. The laboratory device 300 according to this embodiment is designed as a rotary evaporator. The movable element is formed by an evaporation flask 10b.

[0064] The evaporator flask 10b is connected to the rotor of the stepper motor via a shaft 12b

[0065] 20. The shaft 12b can be designed as a hollow shaft through which a vapor passage 16 is inserted into an opening 17 of the evaporator piston 10b and seals it.

[0066] During operation of the rotary evaporator, the evaporation flask 10b is partially immersed in a heating bath (not shown) and rotated. The heat supplied by the heating bath evaporates a portion of a substance contained in the evaporation flask 10b and is passed through the vapor passage 16, for example, into a condenser (not shown).

[0067] To drive the evaporation flask 10b, the laboratory device includes the drive device 50 containing the stepper motor 20 and the control unit 30, and the power supply 40, as described in the first embodiment. Thus, the advantageous effects of the first embodiment can also be achieved in a rotary evaporator.

[0068] Fig. 5 is a schematic representation of a laboratory device 400 according to a fourth embodiment. The laboratory device 400 according to this embodiment is designed as a shaking and mixing device. The movable element is formed by a shaking platform 10c. The shaking platform 10c is connected to the rotor of the stepper motor 20 via a shaft 12c.

[0069] During operation of the shaker-mixer, the shaking platform 10c is set into an oscillating motion, for example, by rotation of the shaft 12c, depending on its bearings and the type of connection to the shaft 12c. This causes substances in vessels (not shown) placed on the shaking platform 10c to be shaken and mixed.

[0070] To drive the shaking platform 10c, the laboratory device 400 includes the drive device 50 containing the stepper motor 20 and the control unit 30, and the power supply 40, as described in the first embodiment. Thus, the advantageous effects of the first embodiment can also be achieved in a shaking-mixing device. The embodiments described above are to be understood as non-limiting examples. The drive device according to the invention can also be used in other types of laboratory devices that have a movable element.

Claims

CLAIMS 1. Laboratory device with a movable element (10, 10a, 10b, 10c) and a drive device (50) for moving the movable element (10, 10a, 10b, 10c), wherein the drive device (50) contains a stepper motor (20) and a control unit (30) for controlling the stepper motor (20), wherein the control unit (30) is designed to control the stepper motor (20) by means of a field-oriented control.

2. Laboratory device according to claim 1, wherein the movable element (10, 10a, 10b, 10c) is connected to the stepper motor (20) without a gear.

3. Laboratory device according to claim 1 or 2, wherein the movable element (10, 10a, 10b, 10c) is connected to a rotor (22) of the stepper motor (20) via a shaft (12, 12a, 12b, 12c).

4. Laboratory device according to one of claims 1 to 3, wherein the field-oriented control is designed such that the speeds and / or torques required for driving the movable element (10, 10a, 10b, 10c) are generated directly by the stepper motor (20).

5. Laboratory device according to one of claims 1 to 4, wherein the drive device (50) further includes a two-phase inverter (31) for generating a two-phase alternating voltage (VAC) from an input direct voltage (VDC), the output of the two-phase inverter (31) being connected to the stepper motor (20) via two motor leads (31 a, 31 b).

6. Laboratory device according to one of claims 1 to 5, wherein the stepper motor (20) includes an encoder (23) for outputting an encoder signal (E) containing information about a position of the rotor (22) in the stepper motor (20).

7. Laboratory device according to claim 6, wherein the control unit (30) contains a position and speed determination unit (34) for determining a rotor angle (q>), an actual position (P) and an actual speed (n) from the encoder signal (E) output by the encoder (23) and from current measurement signals (Ia, Iß) which reflect the currents flowing in the two motor supply lines (31a, 31b).

8. Laboratory device according to claim 7, wherein the control unit (30) further includes a first controller (35), preferably a PI controller, for generating a target speed (nz) from a deviation between a predetermined target position (Pz) and the actual position (P).

9. Laboratory device according to claim 8, wherein the control unit (30) further includes a second controller (36), preferably a PI controller, for generating a target control signal (Iqz) ​​from a deviation between the target speed (nz) and the actual speed (n).

10. Laboratory device according to claim 9, wherein the control unit (30) further includes: a first transformation unit (32) for performing a Park transformation to generate a first control signal (Iq) and a second control signal (Id) from the current measurement signals (Ia, Iß) and the rotor angle (ωp), a third controller (37), preferably a PI controller, for generating a third control signal (Vq) from a deviation between the target control signal (Iqz) ​​and the first control signal (Iq), a fourth controller (38), preferably a PI controller, for generating a fourth control signal (Vd) from the second control signal (Id), and a second transformation unit (33) for performing an inverse Park transformation to generate voltage control signals (Va, Vß) from the third control signal (Vq), the fourth control signal (Vd) and the rotor angle (ωp), wherein the voltage control signals (Va,Vß) are applied to the two-phase inverter (31) for controlling the generation of the two-phase alternating voltage (VAC)., 11. Laboratory device according to claim 10, wherein the control unit (30) further includes a torque maximum determination unit (80) for calculating a maximum torque (Mmax), and the second controller (36) is designed to generate the target control signal (Iqz) ​​taking into account the maximum torque (Mmax) calculated by the torque maximum determination unit (80).

12. Laboratory device according to claim 10 or 11, wherein the control unit (30) further includes: a torque current determination unit (81) for calculating a value of the first control signal (Iq) required to achieve a predetermined torque, and a torque current limiting unit (82) for limiting the value of the first control signal (Iq) calculated by the torque current determination unit (81).

13. Laboratory device according to one of claims 10 to 12, wherein the control unit (30) further includes a decoupling network (84) for decoupling the control for the first control signal (Iq) and the second control signal (Id).

14. Laboratory device according to one of claims 1 to 13, wherein the laboratory device is a laboratory stirrer (100), a peristaltic pump (200), a rotary evaporator (300) or a shaker-mixer (400).

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