JPH076827B2 - Load detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a load detector including a protection unit that protects a mechanism for detecting a load when an excessive load is applied.

[Conventional technology]

A load detector that detects a load acting on an object is used in many fields. Especially in the field of robots,
The system controls the load according to the applied load.

Various types of load detectors have been proposed, and one of them will be described with reference to the drawings. FIG. 4 is a perspective view of a conventional multi-axis load detector. In the figure, 1 and 2 are rings of the same size, and 3a, 3b and 3c are beams connecting the rings 1 and 2, respectively. Reference numeral 4 is a strain gauge attached to each beam at a predetermined position, two sheets at a time. The load detector 5 is configured by these. In addition, X, Y, and Z indicate coordinate axes.

When a load is applied between the ring 1 and the ring 2, the beams 3a, 3b, 3c are flexed accordingly, and strain is generated in each strain gauge according to this flexure, and the resistance value of the strain gauge depends on this strain. Change. The load can be detected by extracting the change in the resistance value as an electric signal using a bridge circuit or an amplifier. The load detector 5 shown is X
It is possible to detect force components F _X , F _Y , F _{Z in the} directions of the axes, Y-axis, and Z-axis and moment components M _X , M _Y , M _Z around the X-axis, Y-axis, and Z-axis.

When the load detector 5 is used for a curved surface polishing work or deburring work of a work performed by a robot, the load detector 5 is installed at an appropriate place of the robot, for example, a wrist portion. Since the processing reaction force changes variously according to the state of the work during the above-mentioned work, the magnitude and direction of the processing reaction force are detected by the load detector 5, and the robot is controlled by a computer so that these values become appropriate values. If it is controlled, the surface polishing and deburring can be performed.

[Problems to be solved by the invention]

By the way, during the work by the robot, if the computer runs out of control for some reason, or if an obstacle enters the operating area of the robot, an unexpected collision occurs in the robot and the load detector 5 Excessive external force may be applied due to this collision. Such a situation occurs not only in the robot but also in the load detector 5 attached to a normal working machine due to an operation error or an intrusion of an obstacle.

When an excessive external force acts on the load detector 5 in this way, the beams 3a, 3b, 3c, which are originally designed to have low rigidity to improve the detection sensitivity, are damaged, and eventually the load detector 5 is destroyed. Will be. In addition, in order to prevent the load detector 5 from being broken in this way, the pillars 3a, 3b,
A means to directly transfer the load between the rings 1 and 2 without going through 3c is conceivable, but applying such means to the load detector requires complicated processing and adjustment, and an expensive detector is required. This leads to the unfavorable situation of making it more expensive.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a load detector capable of preventing the detection portion from being destroyed by an excessive external force with a simple structure.

[Means for solving problems]

In order to achieve the above object, the present invention provides two rigid body parts,
And a load detecting section composed of a flexure section connecting these rigid body sections, and a protective section connected to one of the rigid body sections, and the protective section constitutes a transmission path of a load acting on the load detecting section. In addition, the structure is such that the structure is destroyed when a predetermined load equal to or less than the allowable load of the load detection unit is applied.

[Action]

An external load acts on the load detection unit via the protection unit. When the applied load is less than a specified value, the load is transmitted to the load detection part as it is, but when the applied load exceeds the specified value, the structure of the protection part is destroyed, and such an excessive load occurs. To prevent the transmission of excessive load to the load detector.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiments.

FIG. 1 is a perspective view of a load detector according to an embodiment of the present invention. In the figure, the same parts as those shown in FIG. 4 are designated by the same reference numerals. Reference numeral 6 denotes a load detection unit composed of the rings 1, 2, beams 3a, 3b, 3c and the strain gauge 4. The load detector 6 is the fourth
It has the same structure as the load detector 5 shown in the figure and has the same load detecting function.

Reference numeral 11 is a ring connected to the ring 2 of the load detector 5 by an appropriate means such as a bolt, 12 is the other ring provided so as to face the ring 11, and 13a, 13b and 13c connect the rings 11 and 12. It is a beam. The rings 11, 12 and the beams 13a, 13b, 13c constitute a protection portion 14. The outer shape of the protection unit 14 is substantially the same as the outer shape of the load detection unit 6, and the beams 3a, 3b,
3c and each beam 13a, 13b, 13c of the protection unit 14 are arranged at substantially corresponding positions.

Here, the beams 3a, 3b, 3c of the load detection unit 6 and the beams 13a, 3a of the protection unit 14,
13b and 13c will be described. The beams 3a, 3b, 3c are made of a high-quality elastic material that is rich in ductility because it is necessary to detect the strain generated by the load acting on the load detection unit 6. Such materials include, for example, copper, brass and 0.1% C steel, the characteristics of which are shown in FIG. 2 (a). In Fig. 2 (a), the horizontal axis is strain,
Stress is plotted along the vertical axis. In general, such a material has a large strain until it breaks beyond the elastic limit, that is, a large elongation. And such a property has no protection function.

On the other hand, as the material of the beams 13a, 13b, 13c of the protection portion 14, a material having poor ductility and brittleness is selected. Cast iron is one such material. The characteristics of cast iron are shown in FIG. 2 (b). Similar to FIG. 2A, FIG. 2B also shows strain on the horizontal axis and stress on the vertical axis. As is clear from the characteristics shown in the figure, the cast iron shows almost no elongation even when a load is applied, leading to fracture. By selecting the thickness and width of the beams 13a, 13b, 13c made of cast iron, the load at which the beams 13a, 13b, 13c break can be determined.

Next, the operation of this embodiment will be described. Beams 13a, 13 of the protection part 14
The b and 13c are configured to be destroyed by a predetermined load equal to or less than the load allowed by the load detection unit 6. When a load having a value smaller than the predetermined load is applied to the load detector 15, the load is applied to the ring 1, the beams 3a3b and 3c, the ring 2, the ring 11 and the beams 13a and 1a.
3b, 13c, transmitted through the path of the ring 12, strain is generated in the beams 3a, 3b, 3c of the load detection unit 6 in response to this, and the strain is taken out by the strain gauge 4 and the applied load is detected. .

On the other hand, since the beams 13a, 13b, 13c of the protection portion 14 are made of cast iron having the above-mentioned characteristics, the plastic deformation before the fracture is extremely small, and therefore, in the range of the predetermined load, In the state of use, the load detection unit 6 is not adversely affected, and its detection accuracy is kept good.

Here, if a load larger than the predetermined load is applied to the load detector 15 for some reason, the load is applied to the beam 13 of the protection portion 14.
Since it is transmitted to a, 13b, 13c, any or all of these beams 13a, 13b, 13c are destroyed. Therefore, the load is not transmitted to the load detection unit 6, and the destruction can be avoided. Protection part like this
When 14 is destroyed, the load detector 15 can be constructed immediately by removing the destroyed protection part 14 and receiving a new protection part.

As described above, in this embodiment, the load detection unit and the protection unit are connected in series as viewed from the load transmission path.
It is possible to protect the expensive load detector from damage.
Further, since cast iron is used for the beam of the protection portion, there is almost no plastic deformation in the normal use state, and the detection accuracy can be maintained.

Further, since each beam of the load detection unit and each beam of the protection unit are arranged at substantially corresponding positions, even when a large load acts on a specific beam among the beams of the load detection unit, The load acts on the beam of the protection portion corresponding to the beam as it is, and the beam is immediately destroyed, whereby the reliability of protection can be improved.

FIG. 3 is a perspective view of a load detector according to another embodiment of the present invention. In the figure, the same parts as those shown in FIG. Reference numeral 16 is a flexible diaphragm provided between the ring 11 and the ring 12 of the protective portion 14. This embodiment differs from the previous embodiment in that the diaphragm 16
Is provided, and the other structures are the same.

When an excessive load acts on the load detector 15, any or all of the beams 13a, 13b, 13c are destroyed as described above. By the way, when the load detector 15 is used, the ring 1 is connected to one object and the ring 2 is connected to the other object,
Usually, the load detector 15 and the other of the three objects work together as a unit. For example, in the case of performing curved surface grinding of a workpiece by a robot, the one object is a hand part of the robot and the other object is a grinding tool. Therefore, if all of the beams 13a, 13b, 13c are broken, the grinding tool may fall out of the robot's hands together with the ring 12, damaging the work or other objects, or damaging the grinding tool itself. There is. The diaphragm 16 prevents such a situation, and even if the beams 13a, 13b, 13c are all broken, the ring 11 and the ring 12 are connected by the diaphragm 16 and are not separated from each other. Therefore, it is possible to prevent the situation where the grinding tool in the above example falls off.

A plurality of springs may be used instead of the diaphragm 16.

In this way, in this embodiment, since the two rings of the protection portion in the previous embodiment are connected by the elastic member, the same effect as that of the previous embodiment is obtained, and all the beams of the protection portion are destroyed. Can also maintain the engagement of the two rings.

In the description of each of the above embodiments, cast iron was used as an example of the material for the beam of the protective portion, but the material is not limited to cast iron, and any material having similar characteristics can be used. However, a material other than metal such as ceramics may be used as a matter of course. Also, if the cross-sectional shape or the like is selected as the material of the beam, the same material as that of the beam of the load detector can be used, but in this case, a load close to the breaking load is applied during normal use. When this happens, the beam will break after being plastically deformed, and it is inevitable that the detection accuracy will be adversely affected during use during this period.

〔The invention's effect〕

As described above, in the present invention, since the load detection unit and the protection unit are connected in series as viewed from the load transmission path, the expensive load detection unit can be protected from breakage by a simple structure. .

[Brief description of drawings]

1 is a perspective view of a load detector according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are characteristic diagrams of materials of a load detector and a protector of the load detector shown in FIG. FIG. 3 is a partially broken perspective view of a load detector according to another embodiment of the present invention, and FIG. 4 is a perspective view of a conventional load detector. 1,2,11,12 …… ring, 3a, 3b, 3c, 13a, 13b, 13c …… beam,
4 ... Strain gauge

Claims (5)

[Claims] 1. A load detection unit having a first rigid body portion, a second rigid body portion, and a flexure portion connecting between these rigid body portions, and a load detection portion for detecting a load acting between these rigid body portions; Second
And a protection part that is connected to the rigid body part to configure a transmission path of a load acting on the load detection part and is destroyed by a predetermined load equal to or less than the allowable load of the load detection part. Load detector 2. The protection part according to claim 1, wherein the protection part is a third rigid part connected to the second rigid part, and a fourth rigid part is connected to the load detection target part. And a flexure portion that connects the third rigid body portion and the fourth rigid body portion to each other. 3. The load detector according to claim (2), wherein the flexible portion is made of a brittle member. 4. The load detector according to claim (2), wherein the third rigid body portion and the fourth rigid body portion are connected by a flexible member. 5. The load detector according to claim (2), characterized in that the bending portion of the protection portion has a positional relationship substantially corresponding to the bending portion of the load detecting portion.