JP3249074B2 - Force detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a force detector having a novel structure for measuring force.

[0002]

2. Description of the Related Art A load cell is used as one method for measuring a load.
Load cells are often integrally cut from a rectangular metal block. For example, as shown in FIG. 7, a measuring unit 4 having a roberval mechanism provided with a flexure 3 by cutting and incising a plate-shaped metal block 1, providing a roughly gourd-shaped exfoliated portion 2 in the center, and providing a flexure 3. The strain gauge 5 is attached to the flexure 3 of the Roberval mechanism, and the load F is measured as a load cell.

[0003]

However, in this case, it is extremely troublesome to form the substantially gourd-shaped exfoliated portion 2, and the processing time is increased and the cost is increased. In addition, the thickness of the flexure 3 can be measured only by inserting a vernier caliper from the side, and there is a problem that the thickness control of the flexure 3 which affects the measurement accuracy tends to be insufficient. Furthermore,
When attaching the strain gauge 5 to the flexure 3,
It is necessary to insert the strain gauge 5 from a gap, and it is not easy to confirm the attached state in detail even after completion.

Further, when fixing the load receiving portion to the force receiving portion of the load cell, the flexure 3 is likely to be subjected to a torsional moment and must be attached with care so as not to be damaged.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a force detector which is easy to be processed, can be reduced in size, and has high rigidity without using a flexure.

[0006]

A force detector according to the present invention for achieving the above object has a force receiving member provided outside a metal column having one end as a free end of a force receiving portion and the other end as a fixed end. The cylindrical portion is spaced apart, one end of the cylindrical portion is connected to the force receiving portion, and strain gauges are attached to different positions in the longitudinal direction between the force receiving portion and the fixed end of the metal column, The force is detected by calculating a difference between outputs of the strain gauges due to a force applied to the cylindrical portion.

[0007]

FIG. 1 is a side view of a flexure element used in the present invention, FIG. 2 is a front view, and a flexure element 11 is made of, for example, steel.
It is cut into a prismatic shape based on a metal block such as aluminum. One end of the flexure element 11 is a free end 12 serving as a force receiving portion.
The other end is a fixed end 13 and is fixed to the frame 14. At two points A and B separated by a distance L along the longitudinal direction of the middle portion of the strain body 11, strain gauges 15a and 15b are affixed to the upper, lower, left and right side surfaces. Not connected to a bridge circuit. The strain gauges 15 on the upper and lower surfaces are for detecting the force applied to the free end from the vertical direction, and the strain gauges 15 on the left and right surfaces are for detecting the force applied from the left and right directions.

When a force F is applied to the free end 12 from above, the flexure element 11 is deformed, and counterclockwise moments are generated at points A and B, and two sets of upper and lower strain gauges 15 are provided.
Outputs are obtained from a and 15b, and the force F can be detected by subtracting these outputs.

The principle will now be described. In FIG. 1, when a force F is applied to a point C of the free end 12 of the flexure element 11, A
Assuming that the distance between the point and the point C is La, the bending moment Ma at the point A is Ma = F · La.

If the section modulus is Z, the stress at point A is σa = Ma / Z = F · La / Z.

Further, the modulus of longitudinal elasticity of the material of the flexure element 11 is expressed by E
Then, the strain amount εa by the strain gauge 15a is ε
a = σa / E = F · La / (EZ)

Similarly, assuming that the distance between the point B and the point C at the point B is Lb, the bending moment Mb at the point B and the stress σ
b, the strain amount εb by the strain gauge 15b is as follows. Mb = F · Lb σb = F · Lb / Z εb = F · Lb / (E · Z)

Here, when the difference between the bending moments M at the points A and B is obtained, the following equation is obtained: Ma−Mb = F · La−F · Lb = F (La−Lb) = F · L The difference between the stresses σ is as follows: σa−σb = Ma / Z−Mb / Z = (Ma−Mb) / Z = F · L / Z The difference between the strain amounts ε obtained by the two sets of strain gauges 15a and 15b Becomes the following equation. εa−εb = σa / E−σb / E = (σa−σb) / E = FL / (EZ)

Accordingly, the force F to be detected is as follows: F = (εa−εb) (E · Z) / L (1) Even if point C moves and distances La and Lb change, La− Since Lb = L and E and Z are constant, from the difference between the outputs of the two strain gauges 15a and 15b,
The force F can be obtained as in the equation (1). Also, force F
Is applied dispersedly between the points C and B, the equation (1) is applied, and the force F is detected as a resultant force.

In this case, when a force F is applied from above, the strain gauges 15 on the upper surface are stretched and the strain gauges 15 on the lower surface are compressed. The bridge circuit may be configured so as to calculate the difference between the outputs of the gauges 15 and then combine these differences.

Even if the strain gauges 15 are not provided on both the upper and lower surfaces, there is no problem even if the strain gauges 15 are attached only to the upper surface or the lower surface and the difference is obtained.

The force F applied to the flexure element 11 from the left and right directions can be similarly detected. Further, when the force F is applied from an oblique direction between the upper and lower sides and the left and right sides,
The direction and magnitude of the applied force can be obtained from the component force of the force detected in each of the up, down, left, and right directions.

Further, since the flexure element 11 has a constant flexural rigidity and a constant torsional rigidity over the entire length, the generated stress shows a uniform change in stress which does not cause concentrated stress.

FIG. 3 is a cross-sectional view of an embodiment of the present invention. A cylindrical tube portion 16 serving as a force receiving member is provided separately from the strain generating member 11 shown in FIGS. The free end 12 is connected to the strain body 11 via the flange portion 17 of the cylindrical portion 16.

In this case, even if the force F is applied to an arbitrary position on the cylindrical portion 16, the force F can be accurately measured regardless of the position.

The principle will now be described. In FIG. 4, when a force F is applied to the cylindrical portion 16 from above on the tip side of the point B, counterclockwise moments are applied to the points A and B. appear. Assuming that the distance between the point A and the point D is La ′, the bending moment Ma at the point A is Ma = F · La ′.

If the section modulus is Z, the stress at point A is σa = Ma / Z = F · La ′ / Z.

Further, the longitudinal elastic modulus of the material of the flexure element 11 is expressed by E
Then, the strain amount εa by the strain gauge 15a is ε
a = σa / E = F · La ′ / (E · Z)

Similarly, assuming that the distance between the points B and D at the point B is Lb ', the bending moment Mb, stress σb, and strain εb by the strain gauge 15b are as follows. Mb = F · Lb ′ σb = F · Lb ′ / Z εb = F · Lb ′ / (EZ)

Here, when the difference between the bending moments M at the points A and B is obtained, the following equation is obtained: Ma−Mb = F · La′−F · Lb ′ = F (La′−Lb ′) = FL Similarly, the difference between the stresses σ is as follows: σa−σb = Ma / Z−Mb / Z = FL·L / Z The difference between the strain amounts ε obtained by the two sets of strain gauges 15a and 15b is expressed by the following equation. Become. εa−εb = σa / E−σb / E = FL / (EZ)

Accordingly, the force F is expressed as follows: F = (εa−εb) (E · Z) / L (2) From the obtained difference between the outputs of the strain gauges 15a and 15b, regardless of the position of the point D, The force F can be obtained in the same manner as in the previous example.

Further, as shown in FIG.
When applied to the cylindrical portion 16 at a point D intermediate between the points, a counterclockwise bending moment is generated at the point A, and a clockwise bending moment is generated at the point B. The distance between point A and point D to which force F is applied is La ", and the distance between point B and point D is Lb".
Then, the distance L between point A and point B is L = La ″ + L
b ".

The bending moment Ma at the point A is Ma = FL
a ", and the stress σa is σa = F · La ″ / Z, and the strain εa is εa = F · La ″ / (EZ).

At the point B, the bending moment Ma, the stress σb, and the strain amount εb are as follows. Mb = −F · Lb ″ σb = −F · Lb ″ / Z εb = −F · Lb ″ / (E · Z)

Here, the difference between the bending moments M at the points A and B is as follows: Ma−Mb = F · La ″ − (− F · Lb ″) = F (La ″ + Lb ″) = FL Then, the difference of the stress σ is as follows: σa−σb = Ma / Z−Mb / Z = FL · Z / Z, and the difference of the strain ε is as follows. εa−εb = σa / E−σb / E = FL / (EZ)

Therefore, F = (εa−εb) (EZ) / L (3) is obtained.

As described above, even if the point D to which the force F is applied moves within this range, the force F can be obtained because La "+ Lb" = L is constant.

Further, as shown in FIG. 6, when a force F is applied to the cylindrical portion 16 at a point D behind the point A, a clockwise bending moment is generated at both the points A and B.

The distance between point A and point D to which force F is applied is represented by L
a "', and the distance between point B and point D is Lb"', then point A and point B
The distance L to the point is L = Lb "'-La"'.

The bending moment Ma, stress σa, and strain εa at point A are as follows. Ma = −F · La ″ ′ σa = −F · La ″ ′ / Z εa = −F · Lb ″ ′ / (EZ)

Similarly, bending moment M at point B
b, stress σb, and strain amount εb are as follows, respectively. Mb = −F · Lb ″ ′ σb = −F · Lb ″ ′ / Z εb = −F · Lb ″ ′ / (E · Z)

The difference between the bending moments M at point A and point B is: Similarly, the difference between the stresses σ is as follows: σa−σb = Ma / Z−Mb / Z = F · L / Z, and the difference between the strain amounts ε is as follows:・ L / (EZ)

Therefore, F = (εa−εb) (E · Z) / L (4), and even if the point D to which the force F is applied moves within this range, the force F can be accurately calculated regardless of its position. You can ask.

As described above, in this embodiment, the expression (2)
(4) is exactly the same, and detection can be performed in the same manner, regardless of where the force F is applied to the cylindrical portion 16. Also, force F
Can be detected as a combined force of these forces even if the force is dispersed and applied to the cylindrical portion 16. The embodiment can be suitably used, for example, when detecting the force applied to the control stick or the like by canceling out the grip force.

In the embodiment, the cross-sectional shape of the flexure element is a rectangular column, but it may be a round column. However, in this case, it is preferable that the portion where the strain gauge is attached is ground flat.

[0041]

As described above, in the force detector according to the present invention, by disposing a cylindrical portion at a distance outside the strain body and detecting the force applied to this cylindrical portion, for example, It is possible to detect a force applied to an object such as gripping and operating, regardless of the gripping force.

[Brief description of the drawings]

FIG. 1 is a side view of a flexure element.

FIG. 2 is a front view.

FIG. 3 is a sectional view of the embodiment.

FIG. 4 is an explanatory diagram of a detection principle.

FIG. 5 is an explanatory diagram of a detection principle.

FIG. 6 is an explanatory diagram of a detection principle.

FIG. 7 is a side view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Flexure element 12 Free end 14 Fixed end 15 Strain gauge 16 Tube part

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01L 1/22

Claims (2)

(57) [Claims] 1. A cylindrical portion serving as a force receiving member is spaced apart from a metal column having one end as a free end of a force receiving portion and the other end as a fixed end, and one end of the cylindrical portion is connected to the force receiving portion. Connected to the part, the metal pillar
Affixing strain gauges at different positions in the longitudinal direction between the force receiving portion and the fixed end of the force receiving portion, and detecting the force by calculating a difference between outputs of the strain gauges due to a force applied to the cylindrical portion. And force detector. 2. The force detector according to claim 1, wherein the metal pillar is a prism.