Laboratory device having movable element and 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 stepping motor (20) and a control unit (30) for controlling the stepping motor (20). The control unit (30) is designed to control the stepping motor (20) by means of a field-oriented control.

Description

Technical Field

[0001] The present invention relates to a laboratory device having a movable element and a drive device therefor. Background Art

[0002] Laboratory devices are used for laboratory operations, such as those in the fields of physics, chemistry, biology, and pharmacy. Some of these laboratory devices have movable elements, for example, to convey or mix substances by means of such elements. These include peristaltic pumps, vibrating stirrers, laboratory stirrers, and rotary evaporators.

[0003] Such movable elements are typically driven by a DC motor or a shaded-pole motor. However, these types of motors only provide low torque at low speeds. To achieve the torque required for laboratory instrument operation, such motors operate at high speed and are then decelerated to the required speed via a gearbox (reduction gear). Such a drive is complex and contains many parts. On the other hand, designing such a low-speed high-torque motor requires a large motor size and is therefore not suitable for use in many laboratory devices. Summary of the Invention

[0004] An object of the present invention is to provide a drive device for a laboratory instrument and a laboratory instrument having the drive device, which are simplified and contain fewer parts compared to conventional drives.

[0005] This object is achieved by a laboratory device according to claim 1. Further improvements of the present invention are specified in the dependent claims.

[0006] The laboratory device according to the present invention includes a movable element and a drive device for moving the movable element. The drive device includes a stepper motor and a control unit for controlling the stepper motor. The control unit is designed to control the stepper motor by field-oriented control.

[0007] Field-oriented control (FOC), also known as vector control, is a control method aimed at making the excitation magnetic flux and the armature magnetomotive force of the motor as perpendicular to each other as possible. This enables the maximum torque of the motor to be achieved. For this purpose, a control loop with feedback is provided, in which the data recorded on the machine is processed via transformation.

[0008] Implementing the drive device by a stepper motor and controlling the stepper motor by field-oriented control can, for example, simplify the structure of the laboratory device and reduce the number of parts it contains. For example, this can lead to simplifying the production of the laboratory device and reducing the manufacturing cost.

[0009] Preferably, the movable element is connected to the stepper motor without a gear. For example, this can lead to a further reduction in the number of parts, further simplifying the production and further reducing the manufacturing cost.

[0010] Preferably, the movable element is connected to the rotor of the stepper motor via a shaft. The movable element may also be formed by or include a shaft that is drivingly connected to or integrally formed with the output shaft of the stepper motor. For example, this enables the creation of a particularly simple method for connecting the movable element to the stepper motor.

[0011] Preferably, the field-oriented control is designed such that the speed and / or torque required to drive the movable element are directly generated by the stepper motor. "Control design" refers to the design of the dimensions of the individual functional blocks included in the control loop for performing the control. In other words, the design of the control system includes the proper selection of the parameters of the transfer functions of these functional blocks. For example, such a control design can be used to achieve a gearless connection between the movable element and the stepper motor.

[0012] Preferably, the drive device further includes the two-phase inverter for generating a two-phase AC voltage from the input DC voltage, wherein the output of the two-phase inverter is connected to the stepper motor via two motor leads. By controlling the stepper motor using a sinusoidal AC voltage, for example, it is possible to avoid the loss of steps of the stepper motor and reduce the running noise.

[0013] Preferably, the stepper motor includes an encoder for outputting an encoder signal containing information about the position of the rotor in the stepper motor. For example, this enables the performance of field-oriented control of the stepper motor based on the current rotor position.

[0014] Preferably, the control unit includes a position and speed determination unit for determining the rotor angle, actual position, and actual speed based on the encoder signal output by the encoder and the current measurement signal reflecting the current flowing in the two motor leads. For example, this enables the provision of the actual variables of the stepper motor operation required for field-oriented control.

[0015] Preferably, the control unit further includes

[0016] a first controller, preferably a PI controller, for generating a target speed based on the deviation between a predetermined target position and the actual position,

[0017] a second controller, preferably a PI controller, for generating a target control signal based on the deviation between the target speed and the actual speed,

[0018] a first transformation unit for performing a Park transformation to generate a first control signal and a second control signal based on the current measurement signal and the rotor angle,

[0019] A third controller, preferably a PI controller, which is used to generate a third control signal according to the deviation between the target control signal and the first control signal.

[0020] A fourth controller, preferably a PI controller, which is used to generate a fourth control signal according to the second control signal, and

[0021] A second transformation unit, which is used to perform an inverse Park transformation to generate a voltage control signal according to the third control signal, the fourth control signal and the rotor angle,

[0022] wherein the voltage control signal is applied to the two-phase inverter to control the generation of the two-phase AC voltage.

[0023] This selection of individual functional blocks and their arrangement in the control loop enables, for example, a specific structure to be provided for the field-oriented control of a stepper motor.

[0024] Preferably, the control unit further includes a maximum torque determination unit for calculating the maximum torque, wherein the second controller is configured to generate the target control signal considering the maximum torque calculated by the maximum torque determination unit. For example, this can prevent the control loop from becoming unstable at higher speeds.

[0025] Preferably, the control unit further includes: a torque current determination unit for calculating the 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. For example, this can prevent overcurrent and the resulting motor overheating or damage.

[0026] Preferably, the control unit further includes a decoupling network for decoupling the control of the first control signal and the second control signal. This enables, for example, the magnetic flux and torque of the motor to be controlled separately, thereby achieving better motor dynamic performance.

[0027] Preferably, the laboratory equipment is a laboratory stirrer, a peristaltic pump, a rotary evaporator or a vibrating mixer. For example, this enables the effects of the present invention to be applied to corresponding types of laboratory equipment.

[0028] A method for controlling a movable element in laboratory equipment according to the present invention includes connecting the movable element to a stepper motor and controlling the stepper motor by field-oriented control. Preferably, the field-oriented control is designed such that the speed and / or torque required to drive the movable element is directly generated by the stepper motor.

[0029] For example, by using this method and the improvements described below, the same effects as those of the laboratory equipment according to the present invention can be achieved.

[0030] Preferably, the method according to the present invention further includes

[0031] generating a two-phase AC voltage from an input DC voltage using a two-phase inverter and applying the two-phase AC voltage as an operating voltage to the stepping motor,

[0032] outputting an encoder signal including position information about a rotor in the stepping motor through a decoder included in the stepping motor,

[0033] determining a rotor angle, an actual position, and an actual speed by a position and speed determination unit based on the encoder signal output by the encoder and a current measurement signal reflecting currents flowing in the two motor leads,

[0034] generating a target speed by a first controller based on a deviation between a predetermined target position and the actual position,

[0035] generating a target control signal by a third controller based on a deviation between the target speed and the actual speed,

[0036] performing a Park transformation by a first transformation unit to generate a first control signal and a second control signal based on the current measurement signal and the rotor angle,

[0037] generating a third control signal by a third controller based on a deviation between the target control signal and the first control signal,

[0038] generating a fourth control signal by a fourth controller based on the second control signal,

[0039] performing an inverse Park transformation by a second transformation unit to generate a voltage control signal based on the third control signal, the fourth control signal, and the rotor angle, and

[0040] applying the voltage control signal to the two-phase inverter to control the generation of the two-phase AC voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Additional features and advantages of the present invention will become apparent from the following description of exemplary embodiments based on the drawings.

[0042] Figure 1 is a schematic diagram of a laboratory equipment according to a first embodiment of the present invention.

[0043] Figure 2a is Figure 1Schematic block diagram of the drive device included in the laboratory equipment shown in

[0044] Figure 2b is Figure 2a Schematic block diagram of a variant of the drive device shown in

[0045] Figure 3 Schematic diagram of a laboratory equipment according to a second embodiment of the present invention.

[0046] Figure 4 Schematic diagram of a laboratory equipment according to a third embodiment of the present invention.

[0047] Figure 5 Schematic diagram of a laboratory equipment according to a fourth embodiment of the present invention. Detailed implementation

[0048] Embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 Schematic diagram of a laboratory equipment 100 according to a first embodiment.

[0049] According to this embodiment, the laboratory equipment 100 is designed as a laboratory stirrer. The movable element is formed by a stirring rod 10. The stirring rod 10 includes a stirring head 11 and a shaft 12 connected thereto. The stirring rod can be used to stir the substances in a container (not shown) into which the stirring head is immersed.

[0050] A stepper motor 20 is provided to drive the stirring rod 10. During the operation of the laboratory instrument, the stepper motor 20 rotates the stirring head 11 via the shaft 12. The stepper motor 20 includes 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.

[0051] In addition, 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 power to the stepper motor 20 and the control unit 30, the laboratory equipment 100 further includes a power supply 40, such as a wide-range power supply, for generating an internal supply voltage from the main voltage supplied from the outside.

[0052] The control unit 30 is designed to control the stepper motor 20 by field-oriented control. Figure 2a Schematic block diagram of the drive device 50 for explaining this field-oriented control.

[0053] The stepper motor 20 includes an encoder 23, which outputs an encoder signal E containing information about the position of the rotor 22 in the stepper motor 20.

[0054] The control unit 30 includes a two-phase inverter 31 that generates a two-phase alternating voltage VAC from the DC voltage VDC provided by a power supply 40. The output of the two-phase inverter is connected to a stepping motor 20 via two motor leads 31a, 31b. The alternating voltage VAC is applied as an operating voltage to the stator 21 of the stepping motor 20 via the motor leads 31a, 31b.

[0055] The control unit 30 further includes a first transformation unit 32 and a position and speed determination unit 34. The current flowing in the motor power lines 31a, 31b is detected via a current sensor (not shown) and fed as current measurement signals Iα and Iβ to the first transformation unit 32 and the position and speed determination unit 34.

[0056] The position and speed determination unit 34 determines a rotor angle φ, an actual position P, and an actual speed n based on an encoder signal E output by an encoder 23 and the current measurement signals Iα and Iβ. The rotor angle φ represents the angular position of the inner rotor 22 within the stepping motor, ranging from 0° to 360°. On the other hand, the actual position continues to calculate the angle and thus reaches a multiple of 360° when the rotor rotates several times.

[0057] A first controller 35 (which is preferably designed as a PI controller) generates a target speed nz based on the 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 based on the deviation between the target speed nz and the actual speed n.

[0058] The first transformation unit 32 performs a Park transformation and generates a first control signal Iq and a second control signal Id in a two-axis coordinate system having axes d, q that rotates with the rotor, based on the current measurement signals Iα, Iβ, and the rotor angle φ, such that Iq, Id represent time-constant quantities in the stationary case. Id represents the magnetic flux density of the magnetic excitation in the rotor, and Iq represents the torque generated by the rotor. A time variation in speed or torque results in a time variation in Id or Iq.

[0059] A third controller 37 (which is preferably designed as a PI controller) generates a third control signal Vq based on the 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 based on the second control signal Id.

[0060] The second transformation unit 33 performs an inverse Park transformation and generates voltage control signals Vα and Vβ based on the third control signal Vq, the fourth control signal Vd, and the rotor angle φ. The voltage control signals Vα and Vβ are applied to the two-phase inverter 31 and control the generation of the two-phase alternating voltage VAC.

[0061] The dimensions of the respective functional blocks of the control loop are set such that, that is to say, the parameters of the transfer functions of these functional blocks are selected such that the stepping motor 20 directly generates the speed and torque required to drive the movable element 10.

[0062] This allows the movable element to be firmly connected to the stepping motor without any type of transmission in between. Compared with traditional drive devices, the structure is simplified and the number of parts is reduced. For example, this can also reduce production costs.

[0063] Even if a gearbox is provided between the motor and the movable element, its size can be designed with a lower reduction ratio, so that the structure can still be simplified and the manufacturing cost can be reduced. For example, a 1:1 gearbox can also be used.

[0064] Since field-oriented control uses a sinusoidal AC voltage instead of steps as in traditional stepping motor control, step loss does not occur. In addition, the running noise generated by traditional stepping motor control is eliminated, which is very disturbing in many laboratory environments.

[0065] This control system can achieve maximum torque even at the lowest motor speed. By determining the dimensions of the successive functional blocks of the control loop, the position of the movable element in laboratory equipment can be accurately approached and maintained.

[0066] These characteristics make the field-oriented control stepping motor a suitable drive for all types of laboratory equipment with movable elements.

[0067] Figure 2b is a schematic block diagram of a drive device 50', which drive device is Figure 2a a variant of the drive device 50 shown in. The same elements are provided with the same reference numerals and will not be explained again in the following description.

[0068] In addition to the elements of the drive device 50, the drive device 50' further includes a maximum torque 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.

[0069] The maximum torque determination unit 80 receives a first control signal Iq and a second control signal Id and calculates therefrom 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.

[0070] The torque current determination unit 81 receives the output signal of the second controller 36 and calculates the 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 such that the condition Iq 2 + Id2 ≤Imax 2 , where Imax is the maximum current.

[0071] The output signal of the torque current limiting unit 82 is the first reference signal Iqref (the reference signal of the first control signal Iq). The third controller 37 is supplied with the difference signal between the first reference signal Iqref and the first control signal Iq.

[0072] The reference signal generation unit 83 generates a second reference signal Idref (the reference signal of the second control signal Id). The fourth controller 38 is supplied with the difference signal between the second reference signal Idref and the second control signal Id.

[0073] The decoupling network 84 receives the first control signal Iq and the second control signal Id, and is designed to decouple the control of the two components Iq and Id from each other, thereby decoupling 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 suffix FF indicates that the fifth control signal and the sixth control signal are output from the decoupling network 84 in a feedforward manner.

[0074] The first sum signal Vqsum obtained from the third control signal Vq and the fifth control signal Vq_FF, and the second sum signal Vdsum obtained from the fourth control signal Vd and the sixth control signal Vd_FF are provided to the second transformation unit 33.

[0075] Except for this, the operations of all components are the same as those described above for the drive device 50, and will not be described here again.

[0076] Using the drive device 50', the same effects as those of the drive device 50 can be achieved. In addition, by calculating the maximum torque Mmax and considering it in the control, it is possible to prevent the control loop from becoming unstable at higher speeds.

[0077] In addition, current limiting by the torque current determination unit 81 and the torque current limiting unit 82 can prevent overcurrent and the resulting motor overheating or damage.

[0078] In addition, by using the decoupling network 84 to decouple the two components Iq and Id, better motor dynamic performance can be achieved. In addition, this block can also predict the expected open circuit voltage for compensation.

[0079] Figure 3 is a schematic diagram of the laboratory equipment 200 according to the second embodiment. The laboratory equipment 200 according to this embodiment is designed as a peristaltic pump (hose pump). The movable element is formed by a wheel 10a, and rollers 13 are attached to both sides of the wheel. The wheel 10a is connected to the rotor of the stepper motor 20 via a shaft 12a.

[0080] During the operation of the peristaltic pump, the hose 14 is pressed against the housing wall 15 by the roller 13 and thus clamped at these points. The medium contained in the hose between the clamping points is further conveyed within the hose 14 by the rotation of the wheel 10a.

[0081] To drive the wheel 10a, the laboratory device 200 includes a drive device 50 and a power supply 40, and the drive device includes a stepper motor 20 and a control unit 30, as described in the first embodiment. Therefore, the advantageous effects of the first embodiment can also be achieved by using the peristaltic pump.

[0082] Figure 4 is a schematic view of a laboratory device 300 according to the third embodiment. The laboratory device 300 according to this embodiment is designed as a rotary evaporator. The movable element is formed by an evaporator piston 10b.

[0083] The evaporator piston 10b is connected to the rotor of the stepper motor 20 via a shaft 12b. The shaft 12b can be designed as a hollow shaft, and a steam channel 16 is inserted through the hollow shaft into an opening 17 of the evaporator piston 10b and seals it.

[0084] During the operation of the rotary evaporator, the evaporator piston 10b is partially immersed in a heating bath (not shown) and starts to rotate. Due to the heat supplied by the heating bath, a part of the substance contained in the evaporator piston 10b evaporates and is transferred through the steam channel 16 to, for example, a condenser (not shown).

[0085] To drive the evaporator piston 10b, the laboratory device includes a drive device 50 and a power supply 40, and the drive device includes a stepper motor 20 and a control unit 30, as described in the first embodiment. Therefore, the advantageous effects of the first embodiment can also be achieved in the rotary evaporator.

[0086] Figure 5 is a schematic view of a laboratory device 400 according to the fourth embodiment. The laboratory device 400 according to this embodiment is designed as a vibrating mixer. The movable element is formed by a vibrating platform 10c. The vibrating platform 10c is connected to the rotor of the stepper motor 20 via a shaft 12c.

[0087] During the operation of the vibrating mixing device, the shaking platform 10c is set to perform an oscillating movement, for example, by the rotation of the shaft 12c, which depends on its bearings and its connection type to the shaft 12c. This causes the substances in a container (not shown) placed on the vibrating platform 10c to be vibrated and mixed.

[0088] To drive the vibrating platform 10c, the laboratory device 400 includes a drive device 50 and a power supply 40. The drive device includes a stepper motor 20 and a control unit 30, as described in the first embodiment. Therefore, the advantageous effects of the first embodiment can also be achieved in the vibration mixing device.

[0089] The above-described embodiments should be understood as non-limiting examples. The drive device according to the present invention can also be used in other types of laboratory equipment having movable elements.

Claims

1. A laboratory device, comprising: 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) Comprises: 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 field-oriented control.

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

4. The laboratory device according to any one of claims 1 to 3, wherein the field-oriented control is designed such that the speed and / or torque required to drive the movable element (10, 10a, 10b, 10c) is directly generated by the stepper motor (20).

5. The laboratory device according to any one of claims 1 to 4, wherein the drive device (50) further comprises a two-phase inverter (31) for generating a two-phase AC voltage (VAC) from an input DC voltage (VDC), Wherein the output of the two-phase inverter (31) is connected to the stepper motor (20) via two motor leads (31a, 31b).

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

7. The laboratory device according to claim 6, wherein the control unit (30) comprises a position and speed determination unit (34) for determining the rotor angle (φ), the actual position (P), and the actual speed (n) based on the encoder signal (E) output by the encoder (23) and the current measurement signals (Iα, Iβ) reflecting the current flowing in the two motor leads (31a, 31b).

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

9. The laboratory device according to claim 8, wherein the control unit (30) further comprises a second controller (36), preferably a PI controller, for generating a target control signal (Iqz) based on the deviation between the target speed (nz) and the actual speed (n).

10. The laboratory equipment according to claim 9, wherein the control unit (30) further comprises: a first transformation unit (32) for performing a Park transformation to generate a first control signal (Iq) and a second control signal (Id) based on the current measurement signals (Iα, Iβ) and the rotor angle (φ), a third controller (37), preferably a PI controller, for generating a third control signal (Vq) based on the 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) based on the second control signal (Id), and a second transformation unit (33) for performing an inverse Park transformation to generate voltage control signals (Vα, Vβ) based on the third control signal (Vq), the fourth control signal (Vd), and the rotor angle (φ), wherein the voltage control signals (Vα, Vβ) are applied to the two-phase inverter (31) to control the generation of the two-phase AC voltage (VAC).

11. The laboratory equipment according to claim 10, wherein the control unit (30) further comprises a maximum torque determination unit (80) for calculating the maximum torque (Mmax), and the second controller (36) is designed to generate the target control signal (Iqz) considering the maximum torque (Mmax) calculated by the maximum torque determination unit (80).

12. The laboratory equipment according to claim 10 or 11, wherein the control unit (30) further comprises: a torque current determination unit (81) for calculating the 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. The laboratory equipment according to any one of claims 10 to 12, wherein the control unit (30) further comprises a decoupling network (84) for decoupling the control of the first control signal (Iq) and the second control signal (Id).

14. The laboratory equipment according to any one of claims 1 to 13, wherein the laboratory equipment is a laboratory stirrer (100), a peristaltic pump (200), a rotary evaporator (300), or a vibrating mixer (400).

Images