WO2013071933A2

WO2013071933A2 - Matching energy consumption of an electric transformer with energy needed by a linear actuator system

Info

Publication number: WO2013071933A2
Application number: PCT/DK2012/000121
Authority: WO
Inventors: Jeppe Christian Bastholm
Original assignee: Linak A/S
Priority date: 2011-11-14
Filing date: 2012-11-13
Publication date: 2013-05-23
Also published as: WO2013071933A3

Abstract

This invention relates to a method of downscaling idle energy consumption of a transformer having a primary and a secondary side positioned between a linear actuator system connected to the secondary side and an electrical AC supply connected to the primary side, wherein the electrical AC supply e.g. from a supply network is supplying the linear actuator system with electricity and wherein the transformer is adapted for converting the output of the electrical supply to match the input requirements of the linear actuator system The method comprises the steps of connecting and disconnecting the connection between the primary side and the electrical supply for predefined periods. The invention further relates to a device for performing the method and a transformer comprising a device for performing the method.

Description

Matching energy consumption of an electrical transformer with energy needed by a linear actuator system

FIELD OF THE INVENTION

The present invention relates to a method of adjusting energy consumption of a transformer. The invention further relates to a device for adjusting energy consumption of a transformer and a transformer respectively and a control box for controlling a linear actuator comprising such a device. BACKGROUND OF THE INVENTION

Linear actuator systems comprising at least one linear actuator and a control box for controlling the linear actuator are used in different applications such as in connection with adjustable beds, e.g. hospital beds and adjustable tables. Linear actuator systems are low voltage direct current systems. The drive motor of the linear actuators is low voltage e.g. 20-40V DC-motors and the control electronics might be 5-12V DC. The control box normally contains a network power supply based on an electrical transformer with a rectifier and output smoothing circuit. Normally the control box also comprises a rechargeable battery package as a power supply for running the linear actuator system when it is disconnected from the mains. Use of a network power supply based on an electrical transformer has the benefit that it is very reliable, sturdy, can be heavy loaded even momentarily overloaded without damages and it is relatively inexpensive. An example with dual linear actuators is shown in EP 0 372 032 B2 to Eckhart Dewert. A further example with single linear actuators is shown in DE 298 00 016 U1 to Dewert Antriebs- und Systemtechnik GmbH & Co. KG.

The amount of power needed to be delivered from a transformer to the control box of a linear actuator system varies based on the number of actuators in the actuator system being activated or if no actuator is activated and only control lamps or other low energy consumers in the linear actuator system need energy from the electrical transformer. Further, a transformer constantly uses a small amount of idle power, even though there is a much lower need in the actuator system. An example of such varying energy needs is a linear actuator system for a hospital bed. Such a system comprises a control box for controlling linear actuators, but also other features of the actuator are controlled, such as indicator lamps and e.g. underbed lights, see e.g. US 7,874,695 B2 to Linak A/S. The activation of one or more actuators requires a large amount of energy, whereas activation of only underbed light requires a low amount of energy from the transformer.

The focus on a global reduction in energy consumption is quite significant, and it is therefore of great interest to save energy by matching the power consumed by an electrical transformer in or for a linear actuator system with the power actually needed by the linear actuator system.

OBJECT AND SUMMARY OF THE INVENTION

The object of the invention is therefore to solve the above mentioned problem.

This is achieved by the invention as specified in the claims, where the invention relates to a method, a device and a transformer comprising a device and a linear actuator system comprising a device.

Thereby, it is possible to adapt and adjust the delivered power from a transformer to the amount of power needed by the electrical device and easily reduce or raise the delivered power. The amount of power to be delivered can be determined either by measuring the needs or by receiving the information via a communication link, such as a wireless communication link, or it can be preprogrammed in the device. By measuring the current in the primary winding it is possible to calculate the power needed by the electrical device. Thereby the pulses can be adjusted whereby the transformer delivers power matching the needs of the electrical device.

Alternatively the current in the second winding is measured making it possible to more precisely calculate the power needed by the electrical device. Thereby the pulses can be adjusted and consequently the transformer delivers power matching the needs of the electrical device.

The invention can be used in connection with any linear actuator system, e.g. used in connection with adjustable beds or tables. BRIEF DESCRIPTION OF THE DRAWINGS

In the following preferred embodiments of the invention will be described referring to the figures, where figure 1 illustrates a transformer with a downscaling device between the electrical network and a control box in a linear actuator system for a hospital bed, figure 2 illustrates a transformer with a detailed embodiment of the downscaling device between the electrical network and a control box in a linear actuator system for a hospital bed, figure 3 illustrates a transformer with another embodiment of the downscaling device between the electrical network and the control box in a linear actuator system for a hospital bed, figure 4 illustrates a specific embodiment where the primary winding current is being measured, figure 5 illustrates the principles of the logic in the microcomputer handling the disconnecting and connecting of the transformer, and figure 6a-e illustrates examples of connecting and disconnecting timing relative to the AC supply. DESCRIPTION OF EMBODIMENTS

Figure 1 illustrates a transformer 105 with a descaler 103 between the electrical supply (SP) 101 and a control box 109 in a linear actuator system for a hospital bed. The control box is electrically connected to the secondary side 107 of the transformer 105 and the primary side of the transformer is connected to the electrical supply via a descaler 103. Instead of a direct electrical connection between the control box and the primary winding, the descaler has the functionality of disconnecting and connecting the primary winding to the electrical supply in predefined intervals. In an embodiment the descaler functionality could be integrated in the transformer casing, but it could also be a separate unit adapted to be mounted between the electrical supply and the transformer. In yet another embodiment both the transformer and the descaler are integrated in the control box.

Examples are given with a linear actuator system for a hospital bed. The invention can of course be used for any linear actuator system being connected to the electrical supply via a transformer. Figure 2 illustrates a transformer 105 with a detailed embodiment of the downscaling device 103 positioned between the electrical supply 101 and a control box 109 in a linear actuator system for a hospital bed. The descaler 103 comprises a switch 201 for disconnecting and connecting the primary side of the transformer to the electrical supply 101 , and the timing of this disconnecting and connecting is controlled by a processing unit 203 based on the supply signal being input to the processing unit 203.

Figure 3 illustrates an embodiment where the processing unit 203 provides a control signal to a transistor 301 which based on this control signal disconnects and connects the primary winding 106 of the transformer to the electrical supply 101.

The timing of disconnecting and connecting depends on the power needed at the input of the control box. In one embodiment this value could be programmed in the processing unit. Alternatively, the processing unit could receive this communication wirelessly, e.g. via an optocoupler.

Figure 4 illustrates an embodiment where the processing unit 203 receives input 401 from a sensor measuring the current in the primary winding 108. The amount of current can be used to determine the power needed by the control box. Thereby the timing of disconnecting and connecting can be adjusted and controlled to fit the actual power requirements of the control box. Alternatively, the current in the secondary winding is measured this resulting in a more precise measuring of the power needed by the control box of the linear actuator system.

Figure 5 illustrates the principles of the logic in the microcomputer 203 handling the disconnecting and connecting of the transformer to the electrical supply. The input 307 to the microcomputer is the AC supply signal from the electrical supply, and in 301 it detects characteristics (DT_C) of the AC signal delivered by the electrical supply, whereas in 303 this data, together with input 308 regarding the power needed by the control box of the linear actuator system at the secondary side, is used to determine the timing data for connecting and disconnecting the primary winding to the electrical supply. Finally, in 305 a switch for disconnecting and connecting is controlled based on the determined timing data. The control signal being the output 309 of the microcomputer.

In one example the primary winding is disconnected and then a predefined distance after the AC signal has passed zero the primary winding is connected shortly, where after it is disconnected again. Then the predefined distance after the AC signal has again passed zero the primary winding is connected shortly, where after it is disconnected again. Thereby two pulses are obtained having the same length and in the same distance after the signal has passed zero. After these two pulses have been made the primary winding is disconnected for 0.5-1 second, and then the two similar pulses are made by connecting and disconnecting followed by a similar disconnect period. The pulses in respectively the positive and the negative half period should be identical in order to ensure a uniform output power from the transformer. Figure 6a-6e illustrates curves of the connecting and disconnecting timing relative to the AC supply, where the electrical transformer delivers different amount of energy. More specifically the actual supply signal and the disconnect/connect signal is illustrated. The area below the switching pulses defines the delivered energy, where a small area or a narrow pulse results in a small amount of energy, whereas a larger area results in a larger amount of energy. Note that the pulses do not need to include the AC peak, it is more important that the distance between a zero transition and a positive pulse and a next zero transition and a negative pulse is equal to ensure a balanced output of the electrical transformer. When it is necessary that the transformer delivers power the transformer is connected. This connection could in one embodiment be performed continuously by slowly increasing the width of the positive and negative pulse until the power delivered corresponds to the needs of the control box. Also here the pulses in the positive and subsequent negative half period should be identical to ensure a uniform output power from the transformer.

Alternatively instead of slowly increasing the width, the width can be changed immediately in both the positive and negative pulse to the width required for obtaining the necessary output.

In yet another embodiment the width is slowly changed and the output power is constantly measured and compared to a reference value. Thereby the widths can be changed in a control loop to ensure that the delivered power and the needed power correspond to each other - thereby avoiding waste of power.

Claims

1. A method of adjusting energy consumption of a transformer having a primary and a secondary side positioned between a control box of a linear actuator system connected to the secondary side and an electrical AC supply connected to the primary side, wherein the electrical AC supply e.g. from a supply network is supplying the linear actuator system with electricity and wherein the transformer positioned between the AC supply and the linear actuator system are adapted for converting the output of the electrical supply to match the input requirements of the linear actuator system, the method comprises the step of:

- connecting the primary winding to the AC supply for a predefined pulse interval in respectively a positive half period and a following negative half period of the alternating output from the AC supply, thereby generating a positive and a negative pulse having said pulse interval as pulse width.

2. A method according to claim 1 , wherein the subsequent negative half period is immediately consecutive to the positive half period.

3. A method according to claim 1 , wherein the primary winding is connected at the same predefined distance after the zero transition in respectively the positive half period and the negative half period.

4. A method according to claims 1-2, wherein a positive and a negative pulse are followed by a disconnect period where the primary winding is disconnected from the AC supply.

5. A method according to claims 1-4, wherein the length of the pulse interval and the disconnect period respectively are determined based on the power needed by the linear actuator system connected to the secondary side.

6. A method according to claim 4, wherein the power needed by the linear actuator system is determined by measuring the amount of current in the primary winding of the transformer.

7. A method according to claim 4, wherein the power needed by the linear actuator system is determined by measuring the amount of current in the secondary winding of the transformer.

8. A method according to claim 4, wherein the power needed by the linear actuator system is directly communicated.

9. A descaler for adjusting energy consumption of a transformer having a primary and a secondary side positioned between a linear actuator system connected to the secondary side and an electrical AC supply connected to the primary side, wherein the electrical AC supply e.g. from a supply network is supplying the linear actuator system with electricity and wherein the transformer positioned between the AC supply and the linear actuator system is adapted for converting the output of the electrical supply to match the input requirements of the linear actuator system, said device comprises means for connecting the primary winding to the AC supply for a predefined pulse interval in respectively a positive half period and a subsequent negative half period of the alternating output from the AC supply, thereby generating a positive and a negative pulse having said pulse interval as pulse width.

10. A descaler according to claim 9, wherein said descaler further comprises means for measuring the current in the primary winding.

11. A transformer comprising a descaler according to claim 9 and/or 10.

12. A linear actuator system, wherein said system comprises a descaler according to claim 9 and/or 10.