GB2311612A

GB2311612A - Structure for mounting rod stroke sensor on cylinder actuator

Info

Publication number: GB2311612A
Application number: GB9625711A
Authority: GB
Inventors: Young Il Jin; Soon Yong Yang
Original assignee: Samsung Heavy Industries Co Ltd
Current assignee: Samsung Heavy Industries Co Ltd
Priority date: 1996-03-29
Filing date: 1996-12-11
Publication date: 1997-10-01
Anticipated expiration: 2016-12-11
Also published as: GB2311612B; GB9625711D0; DE19651511A1; JPH09269203A; KR970055317U

Description

2311612 STRUCTURE FOR MOUNTING ROD STROKE SENSOR ON CYLINDER ACTUATOR

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a structure for mounting a rod stroke sensor on a cylinder actuator and, more particularly, to a structural improvement in such a sensor mounting structure for improving the operational precision of the stroke sensor, when the sensor counts the number of magnetic notches formed on the piston rod of the actuator in order to cheek the stroke displacement of the piston rod during movement of the rod.

2. Description of the Prior Art

As well known to those skilled in the art, construction vehicles such as power excavators typically generate excessive operational noises and vibrations and are generally used in poor working conditions, thereby often causing safety hazards while working. It is thus necessary to automate or robotize the operation of construction vehicles. Particularly, the automation or robotization of construction vehicles has been actively studied recently because of a shortage of skilled operators of such vehicles.

In order to effectively automate or robotize the operation of construction vehicles, it is necessary to precisely check movement of working members by checking the displacement of cylinder actuators, for example, a boom cylinder, arm cylinder and bucket cylinder of a power excavator.

In a typical power excavator, the displacement of a cylinder actuator may be directly or indirectly checked. In one indirect method for checking the cylinder actuator's displacement, the rotating angles of individual joints between working members, such as a boom, arm and bucket, may be sensed by respective sensors. In the above case, the displacement of piston rods is checked in accordance with the sensed rotating angles of the joints. Alternatively, the cylinder actuator's displacement may be indirectly checked by an ultrasonic oscillator. which is mounted to each cylinder actuator and checks ultrasonic signals reflected by the tip of an associated piston rod. Meanwhile, in the direct method for checking the cylinder actuator's displacement, a plurality of transformed magnetic notches are formed on each piston rod in a way such that the notches are spaced out at regular intervals. In the above direct checking method, a sensor, which is mounted to the cylinder actuator, counts the number of passed magnetic notches while the piston rod linearly reciprocates relative to the cylinder head of the actuator. thereby checking the displacement of the piston rod.

The indirect checking method, in which the rotating angles of the joints between the working members are sensed, reduces cost of the sensors and provides precise sensing results. so that the method is somewhat effectively used for checking the displacement of a boom or arm cylinder. However, the above method is problematic in that it cannot be used for checking the displacement of a bucket cylinder because the bucket is brought into direct contact with an object thereby exposing the bucket cylinder to extremely poor working conditions.

In this regard, it is preferable to check the displacement of a bucket cylinder by sensing the displacement of the bucket cylinder's piston rod through the above-mentioned direct checking method.

Fig. 1 is a sectional view showing the construction of a cylinder actuator provided with a stroke sensor, which performs the above- mentioned direct checking method. As shown in Fig. 1, the cylinder actuator has a piston 2, which is movably received in a hydraulic cylinder 1 thereby linearly reciprocating in the cylinder 1. A piston rod 3 extends from the piston 2 and projects from one end of the cylinder 1. A plurality of transformed magnetic notches are axially formed on the piston rod 3. The magnetic notches are spaced out at regular intervals. A stroke sensor 4 is mounted to the cylinder actuator, with a space being formed between the sensor 4 and the piston rod 3. The stroke sensor 4 counts the number of magnetic notches while the piston rod 3 linearly reciprocates relative to the cylinder 1, thereby sensing the stroke displacement of the piston rod 3.

However, since the sensor 4 is spaced apart from the reciprocating piston rod 3, the sensor 4 regrettably fails to precisely check the number of the magnetic notches on the rod 3, thereby reducing the sensing operational precision while sensing the stroke of the piston rod 3. The stroke sensor 4 thus provides inferior sensing results. In the above case, the sensed stroke of the piston rod 3 is different from the true stroke of the rod 3, so that the sensor 4 may cause a safety hazard during the operation of a construction vehicle.

When the stroke sensor is mounted. to a position in vicinity to the piston rod in order to overcome the above problem, the sensor may precisely sense the stroke displacement of the rod.

However, this sensor is problematic in that it is thermally affected by the frictional heat generated during the reciprocating motion of the rod.

In an effort to overcome the above problems, Japanese U.M. Laid-open Publication No. Sho. 63-97804 discloses a stroke sensor mounting structure which is shown in Fig. 2. In the above Japanese sensor mounting structure. a stroke sensor 4 is held on a sensor holder 6 as shown in Fig. 2. The tip of the sensor 4, which is brought into contact with a piston rod 3, is coated with a nonmagnetic thin layer 5. Meanwhile, Fig. 3 shows the construction of a stroke sensor mounting structure, which is disclosed in Japanese U.M. Laid-open Publication No. Hei. 4-68202. As shown in Fig. 3, a sensor 4 is installed in a sensor housing 8. The sensor housing 8 is held by a holder 7 which is brought into contact with a piston rod 3.

In the above Japanese sensor mounting structures, a nonmagnetic thin layer is coated on the tip of the sensor which is brought into direct contact with the piston rod.

Therefore, the sensor is rapidly abraded by the frictional abrasion between the sensor and the reciprocating piston rod, so that the expected life span of the sensor is reduced. In addition, the sensor may be badly affected by operational impact or vibrations of the piston rod. The gap between the sensor and the piston rod gradually varies with time due to frictional contact, thus reducing the stroke sensing precision of the sensor.

Another problem of the above Japanese structures resides in that it is very difficult to coat the metal layer on the nonmetal sensor. The frictional heat, which is generated during the reciprocating motion of the piston rod, is directly transferred to the sensor, so that the sensor is thermally affected and thereby often requires replacement, forcing excessive cost to the owner.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a structure for mounting a stroke sensor on a cylinder actuator in which the above problems can be overcome, and which enlarges the contact area between a piston rod and a sensor holder, so that it effectively prevents operational impact or vibrations of the piston rod from being directly applied to the stroke sensor during movement of the rod and thereby improves the sensing operational -precision of the sensor, and which prevents direct contact of the sensor with the piston rod, thus protecting the sensor from frictional heat generated from the reciprocating motion of the rod and lengthening the expected life span of the sensor.

In order to accomplish the above object, the present invention provides a structure for mounting a rod stroke sensor on a cylinder actuator, comprising a sensor holder mounted to a predetermined position of the cylinder head and brought into contact with a piston rod, the stroke sensor mounted to a circuit board fixed to the sensor holder, and a means for enlarging the contact area between the sensor holder and the piston rod and improving the stroke sensing operational precision of the sensor.

In the preferred embodiment of this invention, the contact area enlarging means includes an oilless bearing and a thin plate. The bearing is provided on the lower end of the sensor holder and is brought into contact with the piston rod, thereby reducing the amount 4 of frictional heat generated between the sensor holder and the piston red during movement of the rod. The thin plate holds the sensor and is mounted to the sensor holder at a position where the plate is brought into contact with the piston rod.

- 7 BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional view showing the construction of a cylinder actuator provided with a stroke sensor in accordance with the first prior embodiment, Fig. 2 is a sectional view showing the construction of a stroke sensor mounted to a cylinder actuator in accordance with the second prior embodiment; Fig. 3 is a sectional view showing the construction of a stroke sensor mounted to a cylinder actuator in accordance with the third prior embodiment; and Fig. 4 is a sectional view showing the construction of a stroke sensor mounting structure in accordance with the preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 4 is a sectional view showing the construction of a stroke sensor mounting structure in accordance with the preferred embodiment of the present invention.

As shown in Fig. 4, the stroke sensor mounting structure of this invention has a sensor holder 11. The sensor holder 11 is mounted to a predetermined position of a cylinder head 10 of a cylinder actuator. The lower end of the holder 11 is brought into contact with a piston rod (not shown), which linearly reciprocates relative to the cylinder head 10. A circuit board 14 is fixedly arranged inside the sensor holder 11. The circuit board 14 has a plurality of holes 14A. A stroke sensor 13, which senses the stroke displacement of the piston rod, is mounted to the holes 14A of the circuit board 14 by a sensor mounting protrusion 13A. The sensor mounting structure also includes a contact area enlarging means. The above means enlarges the contact area between the sensor holder 11 and the piston rod, so that the means effectively intercepts operational impact or vibrations of the piston rod during movement of the rod. The means thus almost completely prevents the impact or vibrations from being directly applied to the sensor and thereby improves the sensing operational precision of the stroke sensor. In the preferred embodiment, the contact area enlarging means includes an oilless bearing 12, which is provided on the lower surface of the sensor holder 11. The oilless bearing 12 is brought into contact with the piston rod, so that it reduces the amount of frictional heat generated between the sensor holder 11 and the piston rod during movement of the rod. The contact area enlarging means also includes a thin plate 15, which has a predetermined configuration and holds the lower surface of the sensor 13 thereby preventing the sensor 13 from being unexpectedly separated from the circuit board 14 during movement of the rod. Opposite ends of the thin plate 15 are mounted to the lower end of the sensor holder 11, so that the plate 15 is brought into contact with the piston rod.

In Fig. 4, the reference numeral 16 denotes an electric wire extending from the circuit board 14 to a controller (not shown) of a control system.

In operation of the above sensor 13, the sensor 13 counts the number of magnetic notches formed on the piston rod while the rod linearly reciprocates relative to the cylinder head 10. The sensor 13 thus senses the stroke displacement of the piston rod and outputs a sensing signal indicative of the stroke displacement to the controller. In the above operation, both the oilless bearing 12 and the thin plate 15 enlarge the contact area between the piston rod and the sensor holder 11. The bearing 12 and plate 15 thus effectively prevent operational impact or vibrations of the piston rod from being directly applied to the sensor 13 during movement of the rod. It is thus possible to prevent positional change of the circuit board 14 of the sensor 13. so that the sensing operational precision of the stroke sensor 13 is improved.

The bearing 12 and plate 15 also prevent direct contact of the sensor 13 with the piston rod, thus protecting the sensor 13 from frictional heat generated from the reciprocating motion of the rod. The expected life span of the sensor 13 is, therefore, lengthened. As described above, the present invention provides a structure for mounting a rod stroke sensor on a cylinder actuator. The structure has a means for enlarging a contact area between the sensor holder and the piston rod. The contact area enlarging means includes an oilless bearing, which is provided on the lower end of a sensor holder and is brought into contact with the piston rod. The means also includes a thin plate, which holds the sensor. The thin plate is mounted to the sensor holder and is brought into contact with the piston rod. The bearing and thin plate effectively prevent operational impact or vibrations of the piston rod from being directly applied to the sensor during movement of the rod, so that the sensing operational precision of the sensor is improved. The bearing and thin plate also prevent direct contact of the sensor with the piston rod, thus protecting the sensor from frictional heat generated from the reciprocating motion of the rod and thereby lengthening the expected life span of the sensor.

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible. without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A structure for mounting a rod stroke sensor on a cylinder actuator, comprising: a sensor holder mounted to a predetermined position of a cylinder head of said cylinder actuator and brought into contact with a piston rod: the stroke sensor mounted to a circuit board fixed to said sensor holder; and means for enlarging a contact area between said sensor holder and said piston rod and thereby improving a stroke sensing operational precision of said sensor.

2. The structure according to claim 1, wherein said contact area enlarging means comprises: an oilless bearing provided on a lower end of said sensor holder and brought into contact with said piston rod, thereby reducing the amount of frictional heat generated between said sensor holder and said piston rod during movement of said rod; and a thin plate adapted for holding said sensor. said plate being mounted to said sensor holder in order to be brought into contact with the piston rod.