WO2002003526A2 - A control for two or more dc motors, in particular actuators for adjustment of furniture - Google Patents

A control for two or more dc motors, in particular actuators for adjustment of furniture Download PDF

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Publication number
WO2002003526A2
WO2002003526A2 PCT/DK2001/000470 DK0100470W WO0203526A2 WO 2002003526 A2 WO2002003526 A2 WO 2002003526A2 DK 0100470 W DK0100470 W DK 0100470W WO 0203526 A2 WO0203526 A2 WO 0203526A2
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WO
WIPO (PCT)
Prior art keywords
motors
motor
control
voltage
power supply
Prior art date
Application number
PCT/DK2001/000470
Other languages
French (fr)
Other versions
WO2002003526A3 (en
Inventor
Jeppe Bastholm
Original Assignee
Linak A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Linak A/S filed Critical Linak A/S
Priority to AU2001268959A priority Critical patent/AU2001268959A1/en
Priority to JP2002507494A priority patent/JP2004503194A/en
Priority to US10/312,994 priority patent/US6841953B2/en
Priority to DK01947212.5T priority patent/DK1314234T3/en
Priority to AT01947212T priority patent/ATE496415T1/en
Priority to EP01947212A priority patent/EP1314234B1/en
Priority to DE60143897T priority patent/DE60143897D1/en
Publication of WO2002003526A2 publication Critical patent/WO2002003526A2/en
Publication of WO2002003526A3 publication Critical patent/WO2002003526A3/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P5/00—Arrangements specially adapted for regulating or controlling the speed or torque of two or more electric motors
    • H02P5/46—Arrangements specially adapted for regulating or controlling the speed or torque of two or more electric motors for speed regulation of two or more dynamo-electric motors in relation to one another
    • H02P5/50—Arrangements specially adapted for regulating or controlling the speed or torque of two or more electric motors for speed regulation of two or more dynamo-electric motors in relation to one another by comparing electrical values representing the speeds
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
    • A61G7/00—Beds specially adapted for nursing; Devices for lifting patients or disabled persons
    • A61G7/002—Beds specially adapted for nursing; Devices for lifting patients or disabled persons having adjustable mattress frame
    • A61G7/018—Control or drive mechanisms

Definitions

  • the present invention relates to a control for two or more DC motors, in particular actuators driven by a DC motor for adjustment of furniture, such as tables, beds, chairs, etc, wherein the motors are connected to an adjustable power supply, and wherein the control is adapted to adjust the power supply to the individual motors such that the motors mutually keep the same or essentially the same speed independent of different loads on them.
  • Adjustment of beds and tables is performed using linear actuators of the type which comprises a spindle driven by a reversible DC motor, said spindle being provided with a spindle nut which, either directly or via an extension rod, is connected with the element to be adjusted.
  • linear actuators of the type which comprises a spindle driven by a reversible DC motor, said spindle being provided with a spindle nut which, either directly or via an extension rod, is connected with the element to be adjusted.
  • the prior art for operating linear actuators to obtain uniform travel thereamong is based on a direct or indirect measurement of a distance travelled and a comparison of these.
  • a typical approach is to count the number of revolutions of the spindle or another element in the transmission by an encoder or a rotary potentiometer, e.g. as described in the above US-patent.
  • a comparison of the number of revolutions forms the basis for the control of the motors. It will be appreciated that a certain span of time elapses from a beginning aparallelism between the two actuators before a regulation can be carried out.
  • These controls are relatively expensive and complicated since they are based on computer controls.
  • the object of the invention is to provide a simple and low cost control which may be used for operating two or more actuators to obtain uniform travel thereamong.
  • a pseudomotor is a circuit which electrically behaves like the DC motors concerned, and which is determined on the basis of the electrical properties of the motors.
  • control may be based on a pseudomotor which supplies a voltage corresponding to the speed of the motor on the basis of the energy supplied to the motor, said voltage being used for regulating the power supply.
  • control departs from the previously mentioned controls in that the actuator does not have to travel a distance before an adjustment can take place, but that, instead, the energy transformed in the motor is used as the basis, thus allowing a quicker adjustment to be made.
  • the present control additionally comprises a compensation circuit based on the frequency of the commutator noise from the individual motors, wherein a comparison is made in the compensation circuit of the frequencies from the individual motors, and in case of a deviation of the frequency from one motor relative to the frequencies of the others, the power supply to said motor or to the other motors is adjusted so that the frequencies correspond. This results in a very accurate control of the motors.
  • the speed depends on the con- struction of the actuating device, while the invention adjusts speed through determination of a reference value, as the reference applies the voltage at which the motor should desirably run.
  • a high reference value gives a high speed, and vice versa.
  • the present control may be implemented at low cost and without computer control. It will be appreciated that this does not rule out the possibility that the invention may be used in general for the control of two or more DC motors .
  • Fig. 1 shows a block diagram of an embodiment of the control according to the invention
  • Fig. 2 shows an explanatory block diagram of the control for further understanding of the invention
  • Fig. 3 shows a block diagram illustrating the individual motor.
  • the present control comprises:
  • a power supply 30 7 A delay
  • the power supply comprises a transformer, a bridge coupling and a rectifier capacitor. It supplies the necessary energy to the system and is therefore the "block” that limits the performance of the system with respect to load and speed of the actuators.
  • the voltage is unregulated, therefore is superposed by some ripple when loaded.
  • the reference “block” controls the system, and determines how fast the actuators must/may run.
  • the reference circuit receives information from the two actuators and the power supply, and supplies a reference voltage based on the information that enables the other circuits to stay within their regulation ranges.
  • PI regulator regulates the speed of the individual actuator as close as possible to the voltage (speed) determined by the reference.
  • the regulator contains a proportional part P, to keep the difference small at rapid changes in load, and an integration part I, to make the difference go toward zero over an extended period of time.
  • the PWM power output regulates the energy to the actuator. This is done by quickly connecting the power supply to and disconnecting it from the actuator. The proportion of the connection time and the disconnection time thus determines the supply of energy.
  • the resistor R converts the current running through the actuator into a voltage. This voltage is amplified in the subsequent amplifier so that the output voltage corresponds to the voltage lying across the internal resistance in the motor plus the one lying across the shunt resistance.
  • the RL compensation compensates for current delays caused by the motor which contains a coil. This coil contributes to delaying the current relative to the voltage across the motor, which means that there will always be a time delay between voltage and speed of the motor.
  • band-pass filter extracts the commutator noise from the motor and removes all other noise.
  • the bandwidth of the filter is adapted to the range of speed in which the motor will normally operate (1800-4000 r.p.m.).
  • Phase control Here, the two signals are compared for match/uniformity, and as a result an instantaneous evaluation of the relation of the two signals to each other is emitted.
  • the motors are running at the same speed the two signals are totally identical, phase displaced 90°, and an average value of zero is given and no adjustment is made.
  • the signal from the phase control provides instantaneous values and the double frequency is generated when comparing the two signals, averaging of this signal is needed. This is done by means of the low-pass filter.
  • the explanation is based on a height-adjustable desk having a height-adjustable leg at each side, where the height adjustment is performed with a linear actuator driven by a DC motor.
  • the DC motors I, II of the actuators are connected in parallel to an adjustable DC power supply.
  • a pseudomotor I, II is provided in the inlet to the two motors I, II.
  • a compensation circuit having a signal input from each of the two motors I, II for commutator noise.
  • the actuator concerned i.e. motor II
  • the actuator concerned i.e. motor II
  • the actuator concerned i.e. motor II
  • the actuator concerned will decelerate, and there will be a correspondingly greater current draw, e.g. 3A, which is recognized in the pseudomotor II, so that the voltage from the power supply to the motor will be stepped up correspondingly to 30V.
  • Fig. 3 of the drawing exemplifies an embodiment of the pseudomotor and its mode of operation.
  • the pseudomotor is based on a shunt resistor and an amplifier whose gain is determined on the basis of the formula:
  • the voltage from the amplifier is added to the voltage from the power supply.
  • the voltage to the motor will be increased correspondingly from 26.04V to 30.12V.
  • the motor speeds are adjusted with the compensation circuit until a dominating commutator frequency from the two motors is within a predetermined value. In this respect one motor is picked as a master and the other as a slave to follow this.
  • Trendelenburg adjustments can readily be performed e.g. by activation of one actuator or both of them, but then in their separate directions. If the bed is to be raised or lowered while it is in a Trendelenburg position, the actuators are activated in parallel, i.e. in the same direction and the mattress frame is thereby displaced in parallel.
  • the mattress frame is brought from a Trendelenburg position or an unintentional oblique po- sition to a horizontal position by running it to an extreme position or by control of the actuators.
  • Trendelenburg adjustment, tilting the mattress frame about an axis perpendicular to the mattress frame, is well known and e.g. described in US 4,425,673, see Fig. 7 to 10 and the relating text.
  • the invention is based on model motors and no direct feedback for the evaluation of the current position of the actuators .
  • the invention provides a new way of controlling and regulating two or more actuators so that these run in parallel, irrespective of differences in load, without using microprocessors and feedback other that of the motor in the actuator, in other words no reed switches, hall elements or potentiometers .
  • the invention provides a simple and low cost paral- lei control of two or more DC motors which will meet most requirements to parallel running of actuators within the furniture industry, including nursing and hospital equipment .

Abstract

A control for DC motors, in particular actuators driven by a DC motor for adjustment of furniture, such as tables, beds, chairs, etc. inlcudes a pseudomotor which is capable of supplying a voltage that corresponds to the motor speed on the basis of the current and voltage supplied to the motor. The voltage of the pseudomotor is supplied to an adjustable power supply, where it is compared with an internal reference voltage and adjusts the voltage difference down to the smallest possible difference between the voltage of the pseudomotor and the internal reference voltage. For greater accuracy, the control additionally includes a compensation circuit configured to evaluate a dominating frequency in the commutator noise. Thus, there is provided a simple and low cost control for parallel running of two or more actuators.

Description

A control for two or more DC motors, in particular actuators for adjustment of furniture
The present invention relates to a control for two or more DC motors, in particular actuators driven by a DC motor for adjustment of furniture, such as tables, beds, chairs, etc, wherein the motors are connected to an adjustable power supply, and wherein the control is adapted to adjust the power supply to the individual motors such that the motors mutually keep the same or essentially the same speed independent of different loads on them.
Adjustment of beds and tables is performed using linear actuators of the type which comprises a spindle driven by a reversible DC motor, said spindle being provided with a spindle nut which, either directly or via an extension rod, is connected with the element to be adjusted. For a height-adjustable desk carried by a single leg at each side there is a linear actuator in each leg, and for beds there is one at each end for lifting the mattress frame. US 5 224 429 Haworth Inc. describes such a height adjustable desk and EP 488 552 Huntleigh Technology pic describes a height adjustable bed.
The prior art for operating linear actuators to obtain uniform travel thereamong is based on a direct or indirect measurement of a distance travelled and a comparison of these. A typical approach is to count the number of revolutions of the spindle or another element in the transmission by an encoder or a rotary potentiometer, e.g. as described in the above US-patent. A comparison of the number of revolutions forms the basis for the control of the motors. It will be appreciated that a certain span of time elapses from a beginning aparallelism between the two actuators before a regulation can be carried out. These controls are relatively expensive and complicated since they are based on computer controls.
The object of the invention is to provide a simple and low cost control which may be used for operating two or more actuators to obtain uniform travel thereamong.
This is achieved according to the invention by a control as defined in claim 1.
In the present context, a pseudomotor is a circuit which electrically behaves like the DC motors concerned, and which is determined on the basis of the electrical properties of the motors.
The invention thus realizes that the control may be based on a pseudomotor which supplies a voltage corresponding to the speed of the motor on the basis of the energy supplied to the motor, said voltage being used for regulating the power supply.
It will be appreciated that the control departs from the previously mentioned controls in that the actuator does not have to travel a distance before an adjustment can take place, but that, instead, the energy transformed in the motor is used as the basis, thus allowing a quicker adjustment to be made.
It is recognized that there is a certain deviation in the electrical values of the motors, which results in inaccu- racy in the control. This is obviated in that the present control additionally comprises a compensation circuit based on the frequency of the commutator noise from the individual motors, wherein a comparison is made in the compensation circuit of the frequencies from the individual motors, and in case of a deviation of the frequency from one motor relative to the frequencies of the others, the power supply to said motor or to the other motors is adjusted so that the frequencies correspond. This results in a very accurate control of the motors.
It is known to control a DC motor on the basis of the frequency of the commutator noise, see e.g. DE 33 05 770 Al, page 8 line 11 and on, but the unique aspect of the invention is that the motors are caused to run in parallel by the pseudomotors, while the commutator frequency is used for fine adjustment of the control. Since, beforehand, the commutator frequencies from the individual motors are the same or quite close to each other, the compensation circuit can respond quickly. A control exclusively based on commutator frequency will basically respond too slowly and will also be too complicated and expensive. It should be noted that a linear ac- tuator has a speed, which is typically of the order of 50 mm/sec, i.e. the control must respond relatively quickly to avoid travelling non-uniformly .
In the prior art solutions, the speed depends on the con- struction of the actuating device, while the invention adjusts speed through determination of a reference value, as the reference applies the voltage at which the motor should desirably run. Thus, a high reference value gives a high speed, and vice versa. The present control may be implemented at low cost and without computer control. It will be appreciated that this does not rule out the possibility that the invention may be used in general for the control of two or more DC motors .
The invention will be explained more fully below with reference to the accompanying drawings. In the drawings:
Fig. 1 shows a block diagram of an embodiment of the control according to the invention,
Fig. 2 shows an explanatory block diagram of the control for further understanding of the invention, and
Fig. 3 shows a block diagram illustrating the individual motor.
Referring now to the block diagram in Fig. 1 the present control comprises:
A power supply 30 7: A delay
A reference A band-pass filter
A PI regulator A A/D conversion
A PWM power output 10:A phase control
A R shunt with amplifier 11:A low-pass filter
A RL compensation
Power supply
The power supply comprises a transformer, a bridge coupling and a rectifier capacitor. It supplies the necessary energy to the system and is therefore the "block" that limits the performance of the system with respect to load and speed of the actuators. The voltage is unregulated, therefore is superposed by some ripple when loaded.
2 : Reference
The reference "block" controls the system, and determines how fast the actuators must/may run. The reference circuit receives information from the two actuators and the power supply, and supplies a reference voltage based on the information that enables the other circuits to stay within their regulation ranges.
3. PI regulator The PI regulator regulates the speed of the individual actuator as close as possible to the voltage (speed) determined by the reference. The regulator contains a proportional part P, to keep the difference small at rapid changes in load, and an integration part I, to make the difference go toward zero over an extended period of time.
4. PWM power output
The PWM power output regulates the energy to the actuator. This is done by quickly connecting the power supply to and disconnecting it from the actuator. The proportion of the connection time and the disconnection time thus determines the supply of energy.
5: R shunt with amplifier
The resistor R converts the current running through the actuator into a voltage. This voltage is amplified in the subsequent amplifier so that the output voltage corresponds to the voltage lying across the internal resistance in the motor plus the one lying across the shunt resistance.
6: RL compensation
The RL compensation compensates for current delays caused by the motor which contains a coil. This coil contributes to delaying the current relative to the voltage across the motor, which means that there will always be a time delay between voltage and speed of the motor.
7 : Delay
To find the "internal voltage" of the motor, it is neces- 'sary to subtract the potential cross the internal resistance and the coil in the motor. This is done in a subtraction circuit, but for the result to be correct it is necessary that the signals to be subtracted from each other arrive at the same time. Therefore, a delay is in- troduced in the direct path to the subtraction point, which corresponds to the delay existing in the path through the motor.
8: Band-pass The band-pass filter extracts the commutator noise from the motor and removes all other noise. The bandwidth of the filter is adapted to the range of speed in which the motor will normally operate (1800-4000 r.p.m.).
9: A/D conversion
For these two signals to be compared, they may advantageously be converted into digital values. The values may now be processed according to various logical rules, as needed.
10: Phase control Here, the two signals are compared for match/uniformity, and as a result an instantaneous evaluation of the relation of the two signals to each other is emitted. When the motors are running at the same speed the two signals are totally identical, phase displaced 90°, and an average value of zero is given and no adjustment is made.
11: Low-pass
Since the signal from the phase control provides instantaneous values and the double frequency is generated when comparing the two signals, averaging of this signal is needed. This is done by means of the low-pass filter.
With reference to the explanatory block diagrams in Fig. 2 and 3 the invention is explained in further detail. The diagrams and the values indicated in the diagrams exclusively serve to explain, but not limit the invention. To simplify the description, this takes its point of departure in the ohmic resistances, but the explanation is basically the same for the other electrical phenomena, such as the inductance.
The explanation is based on a height-adjustable desk having a height-adjustable leg at each side, where the height adjustment is performed with a linear actuator driven by a DC motor.
As shown in fig. 2, the DC motors I, II of the actuators are connected in parallel to an adjustable DC power supply. A pseudomotor I, II is provided in the inlet to the two motors I, II. Also present is a compensation circuit having a signal input from each of the two motors I, II for commutator noise.
For example, if the end of the table is suddenly loaded by an additional apparatus when the tabletop is raised, the actuator concerned, i.e. motor II, will decelerate, and there will be a correspondingly greater current draw, e.g. 3A, which is recognized in the pseudomotor II, so that the voltage from the power supply to the motor will be stepped up correspondingly to 30V.
Fig. 3 of the drawing exemplifies an embodiment of the pseudomotor and its mode of operation. The pseudomotor is based on a shunt resistor and an amplifier whose gain is determined on the basis of the formula:
Rjnternal "*" ^shunt Rshunt
The voltage from the amplifier is added to the voltage from the power supply. When the current draw from the motor is increased e.g. from 1A to 3A, the voltage to the motor will be increased correspondingly from 26.04V to 30.12V.
If, because of manufacturing tolerances, the motors do not run at exactly the same speed, the motor speeds are adjusted with the compensation circuit until a dominating commutator frequency from the two motors is within a predetermined value. In this respect one motor is picked as a master and the other as a slave to follow this. In hospital beds with Trendelenburg adjustments, Trendelenburg adjustments can readily be performed e.g. by activation of one actuator or both of them, but then in their separate directions. If the bed is to be raised or lowered while it is in a Trendelenburg position, the actuators are activated in parallel, i.e. in the same direction and the mattress frame is thereby displaced in parallel. The mattress frame is brought from a Trendelenburg position or an unintentional oblique po- sition to a horizontal position by running it to an extreme position or by control of the actuators. Trendelenburg adjustment, tilting the mattress frame about an axis perpendicular to the mattress frame, is well known and e.g. described in US 4,425,673, see Fig. 7 to 10 and the relating text.
The invention is based on model motors and no direct feedback for the evaluation of the current position of the actuators .
As understood from the above, the invention provides a new way of controlling and regulating two or more actuators so that these run in parallel, irrespective of differences in load, without using microprocessors and feedback other that of the motor in the actuator, in other words no reed switches, hall elements or potentiometers .
Thus, the invention provides a simple and low cost paral- lei control of two or more DC motors which will meet most requirements to parallel running of actuators within the furniture industry, including nursing and hospital equipment .

Claims

P a t e n t C l a i m :
1. A control for two or more DC motors, in particular actuators driven by a DC motor for adjustment of furniture, such as tables, beds, chairs, etc, the control is adapted to adjust the power supply to the individual motors such that the motors mutually keep the same or essentially the same speed independent of different loads on them, c h a r a c t e r i z e d in the control comprising a device for adjusting the power supply for each individual motor, a pseudomotor connected to each individual motor, said pseudomotor being constructed to supply a voltage which corresponds to a speed of the motor on the basis of the current and voltage supplied to the motor, wherein the voltages of the pseudomotor supplied to the power supply adjusting device are compared with a common reference voltage, and, when one motor experiences a greater load than the load of the other motors, the reference voltage is reduced such that the power supply to the other motors is reduced reducing the speed of the other motors corresponding to the reduction in speed of the one motor with the greater load.
2. A control according to claim 1, c h a r a c t e r i z e d in that the control additionally comprises a compensation circuit constructed according to a frequency of commutator noise of the motors, wherein a comparison is made in the compensation circuit of the frequencies of the commutator noise of each the motors, and, in case of a deviation of the frequency of one motor relative to the frequencies of the other motors, the power supply to said one motor or to the other motors is adjusted so that the frequencies of the commutator noise of all the motors are within a predetermined value.
3. A control according to claim 2, c h a r a c t e r i z e d in that the frequency of the commutator noise is a dominating frequency
PCT/DK2001/000470 2000-07-05 2001-07-05 A control for two or more dc motors, in particular actuators for adjustment of furniture WO2002003526A2 (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
AU2001268959A AU2001268959A1 (en) 2000-07-05 2001-07-05 A control for two or more dc motors, in particular actuators for adjustment of furniture
JP2002507494A JP2004503194A (en) 2000-07-05 2001-07-05 Control device for two or more DC motors, especially actuators for furniture adjustment
US10/312,994 US6841953B2 (en) 2000-07-05 2001-07-05 Control for two or more dc motors, in particular actuators for adjustment of furniture
DK01947212.5T DK1314234T3 (en) 2000-07-05 2001-07-05 Control for DC motors
AT01947212T ATE496415T1 (en) 2000-07-05 2001-07-05 CONTROLLER FOR TWO OR MORE DC MOTORS, IN PARTICULAR ACTUATORS FOR ADJUSTING FURNITURE
EP01947212A EP1314234B1 (en) 2000-07-05 2001-07-05 A control for two or more dc motors, in particular actuators for adjustment of furniture
DE60143897T DE60143897D1 (en) 2000-07-05 2001-07-05 CONTROL FOR TWO OR MORE DC MOTORS, ESPECIALLY CONTROLLERS FOR THE ADJUSTMENT OF FURNITURE

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DKPA200001048 2000-07-05
DKPA200001048 2000-07-05
DKPA200100092 2001-01-18
DKPA200100092 2001-01-18

Publications (2)

Publication Number Publication Date
WO2002003526A2 true WO2002003526A2 (en) 2002-01-10
WO2002003526A3 WO2002003526A3 (en) 2003-04-03

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DK2001/000470 WO2002003526A2 (en) 2000-07-05 2001-07-05 A control for two or more dc motors, in particular actuators for adjustment of furniture

Country Status (9)

Country Link
US (1) US6841953B2 (en)
EP (1) EP1314234B1 (en)
JP (1) JP2004503194A (en)
CN (1) CN1297064C (en)
AT (1) ATE496415T1 (en)
AU (1) AU2001268959A1 (en)
DE (1) DE60143897D1 (en)
DK (1) DK1314234T3 (en)
WO (1) WO2002003526A2 (en)

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CN1297064C (en) 2007-01-24
EP1314234B1 (en) 2011-01-19
US20030117094A1 (en) 2003-06-26
DE60143897D1 (en) 2011-03-03
CN1441993A (en) 2003-09-10
ATE496415T1 (en) 2011-02-15
US6841953B2 (en) 2005-01-11
AU2001268959A1 (en) 2002-01-14
DK1314234T3 (en) 2011-03-21
WO2002003526A3 (en) 2003-04-03
EP1314234A2 (en) 2003-05-28
JP2004503194A (en) 2004-01-29

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