JP2002247890A - Dc motor power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply device for a linear actuator which is low in cost, prevents a voltage from exceeding an allowable voltage of a low voltage structure, and is free from performance deterioration. SOLUTION: A power supply device for DC motors, in particular for actuators for use in the adjustment of tables, beds and the like, comprises a transformer T1 with a rectifier (D1-D4) and a buffer capacitor. The power supply device comprises voltage limiting means Z1 coupled in parallel with the motor and connected to switch means Q1, so that the motor is connected on a first part of a sine half-wave, but is disconnected when the voltage determined for the voltage limiter is reached. This ensures a proper mean voltage, and the voltage does not exceed an upper permissible value. This also means that the motor speed is more independent of the load, which is advantage, e.g. in case of height- adjustable tables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DC motor,
In particular, it relates to power supplies for actuators for use in adjusting tables, beds, and similar furniture. The power supply includes a primary side for connection to a mains voltage (AC);
A transformer comprising a rectifier and a secondary with a buffer capacitor having at least a terminal for the DC motor and generally also a terminal for the controller.

[0002]

BACKGROUND OF THE INVENTION Linear actuators as stand-alone components are used, for example, in furniture, hospital, and nursing equipment, machines, and to perform various movements and alignments within the manufacturing industry.

[0003] In order to obtain a proper working position with a table or table-like device, it is important that the height of the table top can be adapted to the individual person and his sitting or standing working position. This has traditionally been achieved with more sophisticated tables and equipment, where the cost of the height adjustment itself is less important. However, the recent emphasis on work environments means that more ordinary tables, such as desks, must also be adjustable in height. As a result, the price of height adjustment has become a determining factor. This has led to the field of new products, namely lifting columns for tables that are intended to meet the specific requirements associated with the table. These lift columns are generally based on linear actuators as drive assemblies incorporated into the lift columns, which usually consist of two telescopic links. A control panel, which can be the simplest form of switch, allows the user to adjust the height of the table top as desired.

[0004] For safety and cost reasons, the electrical device of a linear actuator is a low voltage device. This, in addition to being justifiable in terms of safety, means lower cost of components and easier approval procedures, which allows to keep the price of the product at an acceptably low level .

Power supplies for linear actuators generally consist of a transformer with full-wave rectification and smoothing capacitors, which is a simple, reliable and inexpensive power supply, but as the load on the actuator increases, It still has the disadvantage that the motor speed drops relatively sharply. In many situations, it is assumed and anticipated that the speed of the structure will decrease synchronously with the load. In the case of a lifting column for a table, the relatively large difference in speed between an empty table and a loaded table is so great that the user considers this a disadvantage. In particular, the task is therefore to minimize this speed difference for the lifting column within a given framework. For competitive reasons, the solution must be modest in cost or inherently modest in cost.

Since it is desirable to keep the basic structure of the actuator unchanged, in practice it is only possible to consider the power supply and the control of the motor. Since the manufacturing costs associated with the applied solution must be substantially modest, for example, frequency controllers and switch mode power supplies are initially excluded because they are expensive solutions.

[0007] It is therefore an object of the present invention to provide, in terms of manufacturing, less expensive or significantly more expensive than those conventionally used for linear actuators and without exceeding the permissible voltage of low voltage structures. It is to provide a power supply that addresses the problem of degradation.

[0008] With this as a starting point, it has been considered how the utilization of the available output of a given transformer can be optimized while complying with the permissible voltage. According to the Danish high power regulations, the voltage on the secondary side of the transformer is 60V
And the voltage of the low-voltage installation is generally 42.
It cannot exceed 4V.

[0009]

DISCLOSURE OF THE INVENTION The present invention is directed to a method in which a motor is connected in a first part of a sine half-wave and is connected to a motor in parallel, but reaches a voltage determined for a voltage limiter. A power supply device of the kind presented in the opening paragraph, characterized in that it comprises voltage limiting means connected to the switch means so that the motor is disconnected.

[0010] Thus, since the voltage does not exceed the allowable upper limit value, it is possible to achieve the minimum loss of the power supply device while securing an appropriate average voltage. Therefore, the voltage of the power supply is limited at a lower load as compared with the conventional power supply. When the load reaches a certain magnitude, the transformer will not be able to supply sufficient voltage, and the output will drop as in a conventional power supply. For linear actuators, this means that at low loads the speed drop is much less than with a conventional power supply, while at higher loads and the transformer cannot supply enough voltage, the speed drop is less than with a conventional power supply. Means the same size. For example, in the case of a lifting column for a table, this is a considerable improvement over known structures. The relatively large reduction in speed in the last part towards maximum load is very logical for the user and helps to keep the user from overloading the structure.

The voltage limiting means is advantageously formed by a Zener diode, which is a reliable and relatively inexpensive component. A diode with a zener voltage that matches the desired limit of the maximum voltage is selected. It is preferred to choose a diode with a zener voltage of 39V or about 39V, which gives a reasonable safety margin up to the allowed 42.2V.

Conveniently, the switch means is a FET transistor having a gate configured to supply current to the motor when the gate is high, while shutting off current to the motor when the gate is low. F
ET transistors are likewise reliable and inexpensive components. The FET transistor can be controlled by a control device composed of a transistor and a resistor. Since it is configured as a low-side FET transistor, this circuit is implemented such that the FET transistor can turn the coupling fully on and off in a simple manner. A transformer with convenient frequency characteristics can be selected to prevent power loss in the FET transistor.

As a particular feature, the FET transistor is:
A single Zener diode protects against external transients (surge and burst pulses). This same Zener diode serves as a snubbe limiter on the secondary side of the transformer. This diode is
Ensure that the FET transistors are controlled to suppress these unwanted spikes. The main energy from these unwanted voltage spikes is transferred even to the buffer capacitors. Furthermore, it is ensured that the FET transistors are not exposed to voltages exceeding the specification limits.

The invention makes it possible to use a transformer with a higher output (higher voltage), within certain limits of the voltage-20% in a specific example. This potential can be used for higher speeds. AC 230V to A
In the case of a transformer that can be switched to C115V, external power can also be used.
00V.

[0015] Alternatively, the actuator speed can be increased by lowering the impedance of the motor or increasing the spindle pitch. For cost reasons, linear actuators
Motors using permanent magnets are commonly used. To protect the magnet from demagnetization due to the increasing starting current, a soft start or motor current limiting or PWM
Control start can be performed. Soft start is realized by idling the motor for a certain period before stopping, and HW (hardware) or SW (software)
Can be controlled by

However, a soft start of the motor can be performed simply and inexpensively by placing the measuring resistor in the controller at the motor output after the buffer capacitor. During start-up, the measuring resistor is
Limit the voltage to the motor until (electromotive force) is reached.

Another method of utilizing the present invention is to regulate to a lower average voltage, for example, 33 volts, so that the actuator can be speed limited at low loads. This results in a more uniform velocity during fluctuating loads and up and down movements of the lifting column.

Also, the circuit of the power supply can be designed such that the thermal problem is solely due to the transformer,
It must also be shown that this generally has a reconnectable fuse. As a result, operating abuse, such as play with respect to the vertical movement of the adjustable table, is not a thermal problem of the electronic circuit.

In its simplest form, the structure must be able to meet future requirements for power factor. However, power factor can be improved by inserting an additional buffer capacitor in parallel with the rectifier, thereby achieving further voltage smoothing. This capacitor is charged to 60V from the rectifier. Relatedly, the inductance is the source of the FET transistor or the first
Inserted in series with buffer capacitor. In addition, the inductance comprises an idle diode connected to the common power line. This means that the current was not interrupted before and the current curve has a ramp course during the interruption.

A further development of the invention is that the tapping of the current from exactly the same voltage level takes place in the front phase.
ase section). This results in additional current of interest with peaks at each end. The advantage is that the buffer capacitor is charged again before the zero crossing. This results in low voltage ripple and auxiliary draw of current from the transformer during voltage adaptation. The greatest advantage is a reduction in ripple voltage at the desired low output voltage. In addition to this, the power loss of the transformer must be reduced. This can be used for soft start and stop of the motor.

Generally, power supplies are designed to operate with high efficiency, with very low power dissipation in the components.

In certain situations, it may be desirable or desirable to operate the batteries simultaneously or alternately. This can be achieved in that the control circuit lock reset signal is formed in a separate synchronization circuit.

For safety reasons or according to customer specifications, it may be required to power down the power supply when not in use. This is FET
This can be fulfilled by the fact that the transistor can be controlled and turned off, generally by control electronics.

The power supply unit includes means for measuring the current power in the motor, the measurement being used as feedback to regulate the motor voltage so that the motor speed is maintained constant. A special embodiment of is defined in claim 11.

Adjusting the motor voltage to the current power consumption of the motor not only reduces the speed difference, but also keeps the motor speed constant for loads ranging up to the maximum output of the transformer. be able to. At low power consumption, the voltage is small, and as power consumption increases, the voltage increases accordingly. In the case of a lifting column, this means that the table top moves at the same speed, regardless of whether the table is under load or not, whether it is up or down. This is true until the maximum output of the transformer is reached. When a larger load is applied to the table, the speed decreases as the table moves up, as in the case of the conventional power supply unit. Descend at speed. Therefore, the descending speed does not increase with a large load as in the case of the conventional power supply device. This lower, constant lowering speed is gentle on the structure and equipment on the table.

Further, at least on the elevating column, the motor has an overload prevention function, and when it exceeds the maximum size, the current to the motor is cut off. This overload prevention function incorporates a measurement circuit for measuring current, and a signal from this circuit can be used in the present invention, so that the cost can be further reduced.

The motor speed at low load is lower than what the power supply can provide, that is, at maximum load. This is satisfactory in most cases. If higher speeds are desired, compensation for the motor / transformer output should be provided by a mechanical transmission (mechanical
transmission). For example, a spindle with a larger screw pitch can be selected for a linear actuator.

In summary, power efficiency in the circuit is reduced because high efficiency throughout the operating range of the power supply is generally important. Average power supply is 95-9, excluding transformer efficiency.
It is estimated to be 8% or more. Since the FET transistors are arranged as low-side FETs, the circuit is implemented such that the coupling of the FET transistors is completely turned on and off in a simple manner. The circuit is implemented so that the output voltage can be controlled / adjusted. The circuit prevents overvoltage in light of low voltage regulation requirements for a maximum voltage peak of 42.4V. Thanks to this circuit, actuator designers have great freedom in choosing between motor and spindle pitch. This circuit contributes to ensuring a long service life of the relay in the H-bridge.

[0029]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail hereinafter with reference to the accompanying drawings, in which: FIG.

FIG. 1 of the drawings shows a conventional desk provided with a height-adjustable table top plate 1 supported at each end by a lifting column 2 incorporated in an underframe 3. The lifting column has two telescopic links, a stationary link 4 and an extendable link. The extendable link is moved by a linear actuator that includes an electric motor (DC) 5 that drives a spindle via a transmission. The spindle carries a nut on which the piston rod is fixed. The entire actuator is fixed to the stationary link while its piston is fixed to the extendable link. Therefore, the height displacement of the table top is determined by the stroke of the piston rod.

The actuator is connected to the mains voltage via the power supply 6, and the height of the table top can be adjusted up and down by the control panel 7.

The basic structure of the power supply device is clear from the circuit diagram shown in FIG. A power supply with a typical current size of up to 30 A and an average output current of up to 10 A is disclosed, for example, in the Applicant's European Patent Application No. 99600113.7.
As described in the above paragraph, a primary for connection to the mains and one or more DC motors and a connection to a set of relays K1, K2 for controlling the direction of rotation of the motor. Ring or E-core transformer T with secondary side
Based on 1. On the secondary side are a bridge-coupled rectifier D1-D4 for rectifying the AC voltage and a buffer capacitor C1 for smoothing the rectified AC voltage, which is very traditional. In parallel with the motor is a zener diode Z1, which controls via a controller a FET transistor Q1 inserted in series with a rectifier and a buffer capacitor.

As will become apparent, the FET transistors are arranged so that their sources are connected negatively by Graetz coupling. This means that the 100% ON of the N-channel FET transistor can be controlled to limit the ohmic loss to only 20 m. The gist is exactly, 100% related to necessary and desired voltage limits
The adjustment is performed within the range of. As a result, a really high efficiency of the whole power supply is achieved.

[0034] The transformer must be capable of conducting noise.
mains noise filter for ise)
r) and need to specify that the secondary winding constitutes a galvanic separation of electricity from the mains supply, just as it serves as a current limiting impedance to the direct connection of the buffer capacitor. There is.

In view of the half-sine wave, the voltage on the motor and the buffer capacitor increases, and as a starting point the gate of FET transistor Q1 is active. At the same time, a voltage is applied to the Zener diode Z1, here 39
When the Zener voltage reaches V, the control device is activated,
Lower the gate of the FET transistor. This cuts off current to the motor M1 and the buffer capacitor C1, but still applies voltage to them. When the voltage sinusoid returns to zero again, the gate of FET transistor Q2 is activated again, and a new cycle begins.

More specifically, Q1 is a rectifier D1-D
4 functions as a switching element for connecting to the buffer capacitor C1. D5, D6, R7, R6,
When a sufficient voltage is obtained on the secondary winding of the transformer via R5, Q4, R8 and R9, the FET transistor Q1
Are connected. Buffer capacitor C1 is thereby charged to voltage U2, which can be used as a common voltage source for one or more motor H-bridges, with relays K1 and K2 determining the direction of rotation.

The control circuit can be of various shapes,
Here, the locks can be arranged alternately connected to the FET gate. Finally, FET switches often serve as the primary shut-off for the energy supply to the actuator (first error safety).

The Zener diode Z1 has R3, R2,
Limit voltage U2 via Q2, Q3, and R4 and shunt base voltage divider R5, R6 or Q4. this is,
This means that the FET transistor Q1 is turned off for the remaining half sine wave. The locks R2, Q2, Q3, R4 in series with R7, D5 and D6 are released when the sine voltage crosses the zero point, so that a new cycle can be started.

In connection with the switching off of switch Q1, a zener diode Z2 having a zener voltage of 56V is inserted as a protection against excessive voltages caused by the stray impedance of the transformer.

A measuring resistor R1 can be inserted between the buffer capacitor C1 in the control device and the motor connection, said measuring resistor R1 acting as a current limiter for the output current, so that the motor Bring the start. The purpose of the current limiter is to prevent the magnets in the motor from demagnetizing caused by peak currents. Moreover,
The current limiter ensures that the connection of the actuator provides comfortable acceleration without causing severe jerk. In addition, the current limiter helps prevent unwanted draw of current from the transformer. Generally, the current limiter does not operate during normal operation except for connecting the motor or accidentally shutting down the motor. Finally, the current limiter serves as a power limiter for all loads.

In the OFF process after a large amount of current is drawn, F
The ET transistor has a reaction voltage of 7 on the secondary winding of the transformer.
It operates briefly in analog mode with Z2 in series with R8 so that it is limited to less than 0V. This also removes the induced voltage in the primary winding. During the analog period, the current decreases flat to no current, which means that no noise flank occurs. Moreover, it protects the FET switch from unwanted catastrophic overvoltages, even if it originates from the transformer primary.

FIG. 3 of the drawings shows the interrelation curves of the voltage and current courses of the power supply shown in FIG. The curve on the left shows the low load situation corresponding to the table drop,
The curve on the right shows a relatively high load situation corresponding to the lifting of a table loaded with loads. U1 and I1 indicate the voltage and current from the rectifiers D1-D4, and U2 and I2 indicate the voltage and current after the phase cutter.

The power supply itself meets the requirements of future power factor correction. As a consequence, there is a direct possibility to improve the power factor by supplementing the circuit with capacitors, chokes and diodes.

In certain configurations, it may be desirable to provide a battery backup in case of a mains power failure, ie in order to provide alternative battery operation when connection to the mains is not possible at the moment. This is possible in that the reset signal to locks Q2 and Q3 via resistor R7 is formed in a separate synchronization circuit, so that FET transistor Q1 can handle simultaneous or alternating battery operation. . The battery is connected in series with the diode via U1, but the positive pole is connected after the optional measuring resistor.

A further development of the invention is shown in the block diagram of FIG. Here, for example, as described in the applicant's European patent application no.
1 is a set of relays K1 and K2 for controlling the motor.
Is connected to the above-described circuit (hereinafter, referred to as a phase cutter) via an H-bridge. The H-bridge is connected via a FET transistor Q5 to a measurement circuit for measuring the current motor power. The signal output from the measurement circuit is a signal of the phase cutter to the motor in response to the motor power such that the motor speed and thereby the speed of the hoisting pole is maintained constant for loads up to the maximum output of the transformer. It is connected to a phase cutter via a control device for controlling the voltage. For loads exceeding the output of the transformer, the speed drops in tune with the load.

The effect of the present invention is apparent from the three sets of curves shown in FIG. 5 of the drawings. Here, the set of curves on the left represents a conventional power supply with full-wave rectification and buffer capacitors, the set of curves shown in the middle corresponds to the first embodiment and the set of curves on the right. Represents a power supply device according to a second embodiment with sequential voltage control. The upper curve is
The state of the power supply is shown, and the lower curve shows the state of the table. As can be seen, the first embodiment achieves a more uniform speed and the second embodiment achieves a constant speed over a significant range of motor output.

As described above, the motor current is measured by the measurement circuit at the output of FET transistor Q5.
This measuring circuit is shown in FIG. Voltage is measured as an indicator of motor current, said voltage being directly proportional to current. The measurement is
This is performed by the shunt resistor R31. The signal obtained from the measurement is simultaneously used in a conventional manner for overload protection of the motor, and if it exceeds a predetermined maximum size, the current to the motor is cut off. The signal for controlling the phase cutter is obtained from the measuring circuit after the operational amplifier U1-A.

The signal S _I from the measuring circuit is sent to a control circuit for controlling the phase cutter. The signal is amplified by a transistor amplifier, where transistors Q16 and Q17
Are coupled so as to consume no power in the stationary position. The signal is passed from the amplifier via a zener diode D15 having a zener voltage smaller than the zener voltage of the phase cutter.
Sent to node X. This takes over when the voltage on the node exceeds the Zener voltage of the phase cutter. If the zener diode Z1 of the phase cutter has a zener voltage of, for example, 39V and the zener diode D15 has a voltage of 27V, the phase cutter takes over when the amplified measurement signal exceeds 12V. If the signal is less than 12 volts, the phase cutter closes faster than it would otherwise because of the bias of the 27 volt zener diode.

With the above structure, the lifting column based on the linear actuator can maintain a constant speed of about 70 mm / s in a load range of about 0 to 800N.

Thus, the present invention provides a low-cost power supply that simultaneously offers many different possibilities that can be advantageously used in a particular construction. As an alternative to or in combination with zener diode Z1, various alternative or auxiliary voltage references may be used in addition to the time control voltage curve (eg, soft start / stop curve)
It allows to achieve the current / voltage characteristics of a unique power supply.

Regarding the first error security, which addresses the high voltage from the controller, it states that it is possible anywhere in the whole controller.

Although the invention has been described above with particular reference to a lifting column for a table, it is clear that the invention can be used generally in connection with a power supply for an electric motor.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a height-adjustable table to which the present invention can be applied.

FIG. 2 is a circuit diagram showing one embodiment of a power supply device according to the present invention.

FIG. 3 is a graph showing curves of a voltage and a current course of the power supply device.

FIG. 4 is a block diagram of a power supply device according to the present invention.

FIG. 5 is a graph showing an operation mode of the present invention in comparison with that of a conventional power supply device.

FIG. 6 is a circuit diagram of a measuring circuit for the present invention.

FIG. 7 is a circuit diagram of a control circuit for the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H571 CC05 DD01 GG04 HA03 HA09 HA16 HD04 JJ01 JJ26 JJ28 LL22 LL23

Claims (12)

[Claims] 1. A power supply for a DC motor, in particular for an actuator for use in adjusting a table, a bed or the like, comprising a primary for connection to a mains voltage (AC) and a rectifier (D1-D4). And a secondary having a buffer capacitor (C1) which also has at least a terminal for the motor (M1) and a terminal for controlling connection and disconnection of said motor, comprising:
Coupled in parallel with the motor (M1), such that the motor (M1) is connected in the first part of a half sine wave but is disconnected when the voltage determined for the voltage limiter is reached A power supply device comprising voltage / current limiting means connected to the switch means. 2. The power supply according to claim 1, wherein said voltage limiting means is formed by a Zener diode (Z1). 3. The switch means has a gate configured to supply current to the motor (M1) when the gate is at a high level, while cutting off current to the motor when the gate is at a low level. FET transistor gate (Q1)
The power supply device according to claim 1, further comprising: 4. The FET transistor (Q1) comprises a bipolar transistor and a resistor (R3, R2, Q
The power supply device according to claim 3, wherein the power supply device is controlled by a control circuit including (2, Q3, R4). 5. A measuring resistor (R) between a buffer capacitor and a motor connection in the control circuit of the power supply.
The power supply device according to any one of claims 1 to 4, wherein 1) is inserted. 6. A voltage limiter (Z2), preferably a Zener diode, is inserted in series with said FET transistor (Q1).
The power supply device according to any one of claims 1 to 5. 7. An additional buffer capacitor, a choke,
The power supply device according to any one of claims 1 to 6, wherein a coil and a diode are inserted. 8. The power supply according to claim 1, wherein an additional parametric voltage reference is provided in connection with or as an alternative to the zener diode (Z1). . 9. The control circuit according to claim 1, wherein a reset signal for locking the control circuit (Q2, Q3, R7) is formed in a separate synchronous circuit exclusively for simultaneous or alternate battery operation using the FET transistor (Q1) as a switch. The power supply device according to any one of claims 4 to 8, wherein the power supply device is characterized in that: 10. Power supply according to claim 1, wherein the FET transistor (Q1) can be switched off, generally by a control electronic circuit. 11. The power supply includes means for measuring current power in the motor, wherein the measurement is used as feedback for controlling motor voltage such that the speed of the motor is maintained constant. The power supply device according to any one of claims 1 to 10, characterized in that: 12. There is a measurement circuit for measuring the current to the motor for overload protection of the motor, and a signal from this measurement circuit is used as feedback for controlling the motor voltage. The feature of claim 1
2. The power supply device according to 1.