GB2387443A

GB2387443A - Maintaining a relative position between a transmitter and a sensor

Info

Publication number: GB2387443A
Application number: GB0208370A
Authority: GB
Inventors: David John Brown
Original assignee: Lansing Linde Ltd
Current assignee: Linde Material Handling UK Ltd
Priority date: 2002-04-11
Filing date: 2002-04-11
Publication date: 2003-10-15
Anticipated expiration: 2022-04-11
Also published as: DE10314795A1; GB2387443B; GB0208370D0

Abstract

A measuring device for contact-free measurement of positions, displacements and/or angles, and of parameters derivable from these, has a sensor (5) which interacts with a position transmitter (3), and a relative movement between the sensor (5) and the position transmitter (3) can be measured. In order that the measuring device can also be used for position transmitters that are moved relatively imprecisely during operation, and whose distance from a permanently fixed assembly, suitable as a holder for the sensor, is subject to large variations, the sensor (5) is fixed in a sleeve (6) at a defined distance from an open sleeve end, which rests against the position transmitter (3) under spring-loading. The sleeve (6) slides over the position transmitter (3) when the sensor (5) and the position transmitter (3) move relative to each other.

Description

1 2387443

Measuring device for contact-free measurement of positions, displacements and/or angles and of parameters derivable from these The invention concerns a measuring device for contact-free measurement of positions, displacements and/or angles, and of parameters derivable from these, in which a sensor interacts with a position transmitter, and a relative lateral movement between the sensor and the position transmitter can be measured. The invention also relates to an industrial truck having a measuring device of this type.

Measuring devices of the above type that can be used to determine positions, displacements or angles, together with parameters derivable from these, e.g. velocity, acceleration, rotational speed etc., exist in many forms. In these devices the position transmitter moves laterally past the sensor without making contact, or conversely the sensor is moved laterally past the position transmitter without making contact. Inductive, optoelectronic or magnetostrictive systems are used for instance as the measuring principle. The relative change in position can be detected continually or incrementally.

It is often the case that because of the principle of operation of the sensor, a specific distance must be maintained relatively precisely between sensor and position transmitter, otherwise the sensor will malfunction or be unable to work. The sensor must therefore be aligned with the position transmitter with 9 feat precision axially, and the separation must not exceed or fall below a specific distance range, for example 0.5 - 2 mm. In general this requirement does not create insoluble problems. For instance in the measurement of the rotational speed of motors, the position transmitter (e.g. a tooth lock washer) rotates with the motor rotor, which is moved with great precision by means of roller bearings, while the sensor is fixed to the motor housing.

Under these circumstances it is easily feasible to maintain a defined distance between sensor and position transmitter.

An object of the invention is to provide a measuring device of the type specified above that can also be used for position transmitters that are moved relatively imprecisely during operation, and whose distance from a permanently fixed assembly, suitable as a holder for the sensor, is subject to large variations.

According to the invention, the sensor is fixed in a sleeve at a defined distance from an open sleeve end, which rests against the position transmitter under spring-loading, the sleeve sliding

over the position transmitter when the sensor and the position transmitter move relative to each other. The sensor is thereby fixed in a holder in a defined position, which holder may be mounted on bearings allowing a certain degree of "float", and to bring it to rest against the position transmitter under spring action. A defined distance between the sensor and the position transmitter is maintained in this way under all circumstances. When any relative movement occurs between the position transmitter and the sensor, the sleeve-like holder is corrected by means of the spring-loading, and rests continuously against the position transmitter. At the same time the contact-free measurement principle is observed, because the sensor-

constrained by the defined offset from the sleeve end - is not in contact with the position transmitter. According to an advantageous embodiment of the invention, the sensor is mounted in the sleeve so as to allow axial adjustment. This means that the offset from the sleeve end, that is to say the distance from the position transmitter, can be adjusted to lie within the range of distances that allow a correct measurement.

Preferably the sleeve is made of a low-friction material, at least in the area of the open sleeve end, whereby any wear during the movement of the position transmitter relative to the sleeve is minimized. The lowfriction material is preferably a plastics material.

The use of the measuring device according to the invention is particularly advantageous in an industrial truck, in particular for measuring horizontal and/or vertical velocities of a lifting device.

There is also provided an industrial truck, for example, a reach-lift truck having a measuring device of the kind specified above.

Further advantages and features of the invention are explained in more detail with reference to an exemplary embodiment illustrated in the accompanying schematic drawing which is a section through part of a lifting device of a reach-lift truck.

With reference to the drawings, a carriage 1 of a lifting device of a reach-lift truck is moved horizontally in a frame 2, so that in the selected view the carriage 1 moves normal to the _.

drawing plane either towards the viewer or away from the viewer. The frame 2 can be carried, for instance, on a lifting frame allowing vertical movement not shown in the drawing.

A band-shaped linear position transmitter 3 is fixed to the carriage 1 by means of screws 4. The position transmitter 3 is designed, for example, as an incremental position transmitter, i.e. it is made with a multiplicity of recesses 3a giving it a structure similar to that of a comb. The position transmitter 3 is able to move together with the carriage 1, and interacts with a sensor 5 that is held on the frame 2. Thus when the carriage 1 moves in the frame 2 there is a relative movement (into or out of the plane of the drawing shown) between the position transmitter 3 and the sensor 5 and a vertical movement of the sensor 5 in relation to the position transmitter 3 can also freely exist.

The sensor 5 is positioned in a sleeve 6, and fixed there axially, for example screwed in with a locknut 7, as shown in the drawing. In this arrangement the axial position of the sensor 5 is adjusted to give an offset x between the sensor end and the open sleeve end, which lies opposite the position transmitter 3. The sleeve 6 can move axially within a hole 8 of the frame 2, and is pressed towards the carriage 1 by means of springs 9a7 9b, which acts against bracket 10 and locknut 7, until the sleeve 6 comes to rest on the position transmitter 3. By this means the offset x equals the axial distance between the sensor 5 and the position transmitter 3. The offset x is set by screwing the sensor 5 into or out of the locknut 7 so that it lies within the distance range required for the sensor 5 to work properly.

The sleeve 6 is preferably made of low-friction plastics material, which has the advantage that almost no wear results from the sliding of the position transmitter 3 over the sleeve end.

Furthermore there is less noise generated.

Instead of the arrangement employed in this exemplary embodiment, in which two springs 9a, 9b are used to press the sleeve 6 against the position transmitter 3, it is also possible to design the measuring device according to the invention so that only one spring is required.

Claims

1. Measuring device for contact-free measurement of positions, displacements and/or angles, and of parameters derivable from these, in which a sensor interacts with a position transmitter, and a relative lateral movement between the sensor and the position transmitter can be measured, wherein the sensor is fixed in a sleeve at a defined distance from an open sleeve end, which rests against the position transmitter under spring-loading, the sleeve sliding over the position transmitter when the sensor and the position transmitter move relative to each other.

2. Measuring device according to claim 1, wherein the sensor is mounted in the sleeve so as to allow axial adjustment.

3. Measuring device according to claim 1 or claim 2, wherein the sleeve is made of a low-

friction material, at least in the area of the open sleeve end.

4. Measuring device according to claim 3, wherein the low-friction material is a plastics material.

5. Measuring device according to any one of claims 1 to 4, wherein the device is adapted for use in an industrial truck.

6. Measuring device according to claim 5, wherein the device is adapted for measuring horizontal and/or vertical velocities of a lifting device of the industrial truck.

7. Measuring device for contact-free measurement of positions, displacements and/or angles, and of parameters derivable from these substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

8. Industrial truck having a measuring device according to any one of the preceding claims.

9. Industrial truck according to claim 8, wherein the industrial truck is a reach-lift truck.