ACTUATOR SYSTEM

• US 20100005590A1
• Filed: 12/20/2007
• Published: 01/14/2010
• Est. Priority Date: 12/31/2006
• Status: Active Grant

• Current Assignee: Linak A/S (Linak Holding A/S)
• Original Assignee: Linak A/S (Linak Holding A/S)
• Inventors: Jensen, Svend Erick Knudsen
• Granted Patent: US 8,302,227 B2
• Time in Patent Office: Days
• US Class Current: 5/611
• CPC Class Codes: A47C 20/041 by electric motors
• CPC Class Codes: A61G 7/018 Control or drive mechanisms
• CPC Class Codes: F16H 2057/012 of gearings
• CPC Class Codes: F16H 25/20 Screw mechanisms with automatic reversal F16H25/12
• CPC Class Codes: F16H 57/01 Monitoring wear or stress of gearing elements, e.g. for triggering maintenance
• CPC Class Codes: Y10T 74/18576 including screw and nut

Abstract

Today, electromechanical actuator systems are used in a variety of applications, of which some are more safety critical than others. Likewise, they are used in a wide range of applications where the safety of persons often to a higher or lesser extent depends on that the actuators remains safe both during normal use and in the fault conditions, which may occur. By an actuator comprising a DC motor (2) equipped with a worm drive and a spindle (4), the typical wearing components are the bearing, which carries the spindle (4), the spindle nut (5) and the worm wheel (9) in the worm drive. Common to the described defect situations is that they in the time leading up to the occurrence of the defect will show a decrease in the ratio of efficiency. Whether it is the spindle bearing, the worm drive, the spindle nut (5) or for that matter the motor, which is getting worn, the proportion between the current which the motor absorbs and the force the actuator performs will change. The purpose of the present invention is thus to monitor the ratio of efficiency of the actuator. When this begins to change, becomes worse, it is time to replace the actuator before it becomes defective. For this purpose a load cell can for instance be incorporated in the actuator, for measuring the force on the rear mounting. This force is compared with the power consumption and an indicator for the ratio of efficiency can thus be calculated as force/current.

Claims

1. An actuator system comprising at least one electromechanical linear actuator includes a reversible electric motor (2), which via a gear drives a spindle (4) with a spindle nut (5) with an activation element, and a rear mounting (11);

a power supply;

a control unit with a control, and means for monitoring the ratio of efficiency of the actuator.

2. The actuator system according to claim 1, including at least one load cell for measuring the force on the rear mounting (11), this force being compared to the power consumption and thus an indicator for the ratio of efficiency to be calculated as force/current.

3. The actuator system according to claim 1, including a piezoelement as a load cell.

4. The actuator system according to claim 1, wherein a preventive replacement of at least one part of the actuator system is carried out during a routine service visit on the basis of the efficiency.

5. The actuator system according to claim 1, including an online connection to a service center and which automatically requests service and indicate which component(s) are to be replaced in time, before defects occur.

6. The actuator system according to claim 2, incorporated in an apparatus having a weighing system used to calculate the force on the actuator.

7. The actuator system according to claim 6, wherein the apparatus is a hospital bed with a lower frame and a support surface for a mattress, said support surface can be raised and lowered with the actuator(s) and where the bed is equipped with a weighing system in connection with the support surface and having means for calculating the force on the actuator(s) on basis of this weighing system and having means for registering and comparing current (power consumption) with the power and distance (power output).

8. The actuator system according to claim 7, wherein support surface for the mattress in the hospital bed is carried by two actuators in the form of lifting columns, one at each end of the bed, and on basis of the weighing system the force on the actuator is also known, the force is distributed among the two columns, and the centre of gravity on the bed is calculated from the load cells, by what means the force distribution on the bed is also known.

9. The actuator system according to claim 7, wherein the hospital bed has a scissor mechanism for the support surface for the mattress, where the power is compensated for the gear ratio on the scissor.