JPH0775816B2 - Axial force measuring device - Google Patents

Description

The present invention relates to an axial force measurement for measuring a force (hereinafter referred to as an axial force) in a linear movement direction of a table or a spindle head as a linear movement body in a machine tool. Regarding the device.

(Prior Art) Conventionally, this type of axial force measurement is performed, for example, in a machine tool.
It is required to prevent breakage, breakage, etc. of tools, workpieces and other components of machine tools. Then, in the conventional axial force measuring device, in order to measure the axial force on the side of a moving body such as a spindle of a machine tool or a table, a sensor such as a strain gauge is attached to these moving bodies, and the axis of the output signal of this sensor is used to measure the axial force. It was common to measure force.

(Problems to be Solved by the Invention) However, in the conventional axial force measuring device, a power source other than the axial force to be measured is applied as a disturbance by a power transmission mechanism such as a drive source such as a spindle motor and a feed motor or a gear. There is a problem that the desired axial force cannot be measured accurately. Further, the rotating body has a drawback that signal transmission from the rotating body becomes very difficult.

Further, a method of using a 6-component force table using a piezo element or a strain gauge may be considered as an axial force measuring means other than the above, but as is well known, this 6-component force table is generally suitable for medium and small loads. It is not suitable for measuring axial force due to heavy load. Furthermore, the axial force measurement using the 6-component force table must be performed separately and independently from the machining operation by the machine tool, and it takes time and effort to install the 6-component force table on the machine tool and it is possible to perform parallel processing during machining. Axial force measurement,
There is a problem that the processing conditions cannot be changed using the measurement result.

The present invention has been proposed in order to solve the above problems, and an object of the present invention is to accurately measure the axial force of a moving body that moves in a straight line by a load cell without being affected by disturbance or the like. An object of the present invention is to provide an axial force measuring device having a simple structure, which eliminates the trouble of installation by preliminarily incorporating a load cell into a machine tool or the like and enables axial force measurement in parallel with a machining operation.

(Means for Solving the Problems) In order to achieve the above object, the present invention forms a thin portion in a nut portion of a ball screw that drives a linear motion body in a machine tool and fixes a force sensor to the thin portion. The force sensor detects a force from a linear moving body that constitutes a load cell and moves along the axial direction of the ball screw, based on the strain generated in the thin portion.

(Operation) According to the present invention, the force (reaction force) from the moving body that linearly moves along the axial direction of the ball screw is such that the thin-walled portion of the nut portion is relatively stationary with respect to the moving body. Causes distortion. This strain causes an electric signal proportional to the axial force by the force sensor fixed to the thin portion. Therefore, the axial force of the moving body can be measured by measuring this electric signal.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

First, Fig. 1 and Fig. 2 show X, Y, Z of the machining center.
It is an example in the case where the present invention is applied to a nut portion to which a ball screw of each shaft is attached.

For example, FIG. 1 shows a table 30 as a linear moving body,
It is an example in which the present invention is applied to a nut portion 20 of a ball screw 40 for moving along a shaft. In this case, since the table 30 linearly moves integrally with the nut portion 20, the nut portion 20 constitutes a system that is relatively stationary with respect to the linear movement direction of the table.

In the figure, the nut portion 20 screwed to the ball screw 40 is provided with the nut 21 on the arm 31 protruding from the table 30.
Are integrally fixed by.

The nut portion 20 is formed with a wide groove 22 in the outer peripheral surface central portion thereof, and a narrow groove 23 is formed in the inner peripheral surface central portion thereof. Strain gauges 24 as force sensors are fixed to the respective quarter positions. Further, as is clear from FIG. 2 which is an enlarged view of the portion b in FIG. 1, a thin portion 25 is formed between the groove 22 and the groove 23. The inside of the groove 22 to which the strain gauge 24 is fixed is filled with a silicone rubber 26 having a low foaming property or a small elasticity and an oil resistant silicone rubber 27.

In FIG. 2, the wall thickness d of the thin portion 25 is 0.5 m, for example.
m, the width L _{2 of the} groove 23 is 1 mm, and the corner portion 23 of the groove 23 is
a is formed in a radius with a radius of 0.2 mm.

In this way, in this embodiment, the nut portion 20 constitutes a load cell, and this load cell measures the axial force of the table in the X-axis direction (force along the axial direction of the ball screw 40) as follows. .

That is, in FIG. 1, the nut portion 20 moves along the ball screw 40 by the rotational force of the ball screw 40, and along with this, the table 30 moves in the X-axis direction via the arm 31, At this time, assuming that there is no loss of force between the nut portion 20 and the arm 31, the table
The force of 30 in the X-axis direction is directly applied to the thin portion 25 of the nut portion 20 and distorted to generate an electric signal from the strain gauge 24.

In other words, the thin portion 25 of the nut portion 20 shown in FIG. 2 is distorted by the force (reaction force) from the arm 31 of the table 30 that the nut portion 20 receives, which is proportional to the axial force of the table 30 in the X-axis direction. An electric signal can be obtained from the strain gauge 24, and the axial force of the linear moving body can be measured from almost the stationary system side.

Next, FIGS. 3 to 7 show the principle of the present invention applied to the housing of a spindle bearing of a machine tool such as a machining center.

In FIG. 3, reference numeral 1 denotes a main shaft as a moving body which moves linearly, and a plurality of bearings 2 are mounted on the main shaft 1 along the axial direction thereof. Between these bearings 2, the inner ring collar 3 and the outer ring collars 4,5 of the bearing 2
Are appropriately arranged. Further, an inner ring collar 6 which is long in the axial direction is arranged between the inner ring 2A of the uppermost bearing 2 and the head 1A of the main shaft 1.

Further, 7 is a housing for accommodating the bearing 2 and the collars 3 to 6, and an outer ring retainer 8 is provided inside the upper end of the housing 7, and the outer ring retainer 8 is attached to the upper end of the housing 7 by a bolt 9. It can be tightened to.

On the other hand, a ring-shaped axial force sensor collar 10 forming a load cell is mounted between the outer ring 2B of the uppermost bearing 2 and the outer ring retainer 8. This axial force color 10
In the above, the outer ring retainer 8 is tightened to provide a preload in the direction in which the uppermost bearing 2 is brought into pressure contact, and its configuration is as shown in FIG. That is, a wide groove 12 is formed in the central portion of the outer peripheral surface of the ring-shaped main body 11, and a narrow groove 13 is formed in the central portion of the inner peripheral surface of the main body 11, and the groove 12 is formed in the groove 12. Strain gauges 14 are fixedly attached at positions that divide the outer peripheral surface into quarters. Inside the groove 12 to which the strain gauge 14 is fixed, the strain gauge
Silicone rubber 16 is filled to protect 14.

Here, FIG. 5 is an enlarged view of the portion a in FIG. An example of the dimensional relationship of each part will be described based on the figure. Now, the axial force sensor collar 10 up to the bottom surface of the groove 12 is described.
When the diameter D of the groove (see FIG. 4) is 80 mm, the width L _{1 of the} groove 12
Is 4 to 5 mm, and the width L _{2 of the} groove 13 is 1 mm.
The thickness d of the thin portion 15 between 12 and 13 is 0.5 mm.

In addition, the axial force sensor collar 10 is a main body 1 which is a moving body.
Along with this, the spindle head moves linearly as a constituent element of the spindle head, but with respect to the spindle 1, it constitutes a system that is relatively stationary in the axial direction.

Therefore, the relationship between the spindle 1 and the bearing 2 shown in FIG. 3 can be considered as a model of a spring system as shown in FIG. That is, in FIG. 3, when a force is applied to the main shaft 1 along its axial direction, the bearing 2 is elastically deformed. Therefore, as shown in FIG. 6, the bearing 2 is provided with springs 201, 202 (spring constants k ₁ , k ₂ ). On the other hand, 101 in FIG.
Is a main shaft as a moving body, and 301 is the bearing 2 (spring 2
(01, 202) is a substantially stationary system such as the outer ring collars 4 and 5 and the outer ring retainer 8 shown in FIG.

In such a model, a force f ₀ is first applied to the main shaft 101, and in this state, an axial force fex is applied from the outside in the direction of arrow b in FIG. As shown in FIG. 7, the axial force fex is applied to the springs 201, as forces Δf ₁ and Δf _{2 which} are opposite to each other.
Each of them is shared by 202, and the spring 201 generates a displacement Δx according to a displacement characteristic line x ₁ according to its spring constant k ₁ . On the other hand, with respect to the spring 202, the displacement Δx having the same magnitude is generated according to the displacement characteristic line x ₂ due to the spring constant k ₂ .

That is, the axial force fex, the spring constants k ₁ and k ₂ and the displacement Δx have a relationship of fex = Δf ₁ + Δf ₂ = k ₁ Δx + k ₂ Δx = (k ₁ + k ₂ ) Δx.

If the spring constants k ₁ and k ₂ are known, the axial force fex
Can be calculated by obtaining the displacement Δx of the springs 201 and 202.
This displacement Δx can be detected from the substantially stationary system 301 side as is clear from FIG.

In the above model, measuring the displacement Δx from the substantially stationary system 301 side corresponds to measuring the strain due to the bearing 2 from the substantially stationary system in the embodiment of FIG. Axial force sensor color 10 which is a stationary system
By detecting the distortion caused by the bearing 2 at the position
It is possible to measure the axial force of.

That is, in FIG. 3, as described above, the axial force sensor collar 10 is preloaded by the outer ring retainer 8. In this state, the axial force of the main shaft 1 is transmitted from the inner ring collar 6 to the inner ring 2A of the uppermost bearing 2, and then a part of the power is transferred to the inner ring 2A of the next stage bearing 2 → the inner ring collar 3 → the further stage bearing 2 Inner ring 2A → is transmitted through the route. Also,
The balance of the axial force transmitted to the inner ring 2A of the uppermost bearing 2 is the ball of the bearing 2 → the outer ring 2B of the bearing 2 → the outer ring 2B of the bearing 2 of the next stage → the outer ring collar 4 → the outer ring 2B of the bearing 2 of the next stage → ... is transmitted via the route.

Therefore, the reaction force of the force applied to the outer ring 2B is applied to the axial force sensor collar 10 that is always in pressure contact with the outer ring 2B of the uppermost bearing 2, and the thin portion 15 is distorted to cause the shaft of the spindle 1 to rotate. An electric signal proportional to the force can be obtained from the strain gauge 14.

If the axial force sensor collar 10 is arranged immediately below the outer ring retainer 8, there is an advantage that the output electric signal of the strain gauge 14 can be easily taken out from the outer side of the inner ring collar 6, but the position of the axial force sensor collar 10 is increased. Is not limited to this, and may be at positions such as the outer ring collars 4 and 5 in FIG. 3 as long as there is no problem in taking out an electric signal.

Next, FIGS. 8 and 9 show the principle of the present invention applied to an actuator of a machining center incorporating a fail-safe system. The failsafe system and the actuator are disclosed by the inventor in Japanese Patent Laid-Open No. 2-5779.
It was already proposed as No. 5, and its outline is explained below.

This fail-safe system, when a force over the set value is applied from a moving body such as the spindle of a machine tool or a table,
A mover that moves in the direction of this force, a stopper that sets the initial position of this mover, and a force such as a hydraulic mechanism that supports the mover and applies a predetermined constant force to the mover. And a moving body, which detects that the moving body has received a force from the moving body and has moved by a certain displacement, stops the movement of the moving body, and retracts the system to the safe side.

Further, the actuator is a component of the fail-safe system and responds to a force from the moving body, and when a force exceeding a set value is applied from the moving body, the actuator moves along the direction of the force. At least a child and a stopper for setting an initial position of the moving element are supported, and the moving element is supported by a force acting body provided inside or outside to apply a predetermined constant force to the moving element. is there.

For example, FIG. 8 shows a fail-safe system using hydraulic pressure as a force acting body incorporated in a machining center. In the figure, 51 is a column, 52 is a spindle head as a moving body, and 53 is a tool holder 54. A motor for rotating the tool 55, 56 a work, 30 a table as a moving body as described above, 57 a base, 58 a saddle, 40 a ball screw for moving the table 30 in the X-axis direction, 20A Is a nut portion screwed to the ball screw 40.

Further, 59 is an actuator similar to a hydraulic cylinder in principle, and this actuator 59 is between the table 30 and the nut portion 20A, and the main spindle head 52 and the nut portion of the ball screw 60 for moving the main spindle head 52 in the Z direction. It is also provided between the base screw 61 and the ball screw provided between the base 57 and the saddle 58. All the hydraulic pressures from these actuators 59 are connected to one and are connected to an accumulator 62 provided outside. A hydraulic motor 63 is attached to this accumulator 62, and by changing the rotational position of the hydraulic motor 63 by an NC program, the operating point of the actuator 59, that is, the set value of the force applied to the table 30 or the spindle head 52 is 100 kgf, for example. 500kgf, 10
It can be changed to 00kgf.

Next, an example of a specific configuration of the actuator 59 is shown in FIG. Although the actuator 59 provided between the table 30 and the nut portion 20A is shown in FIG. 9,
The actuators provided in other parts have the same basic configuration.

In the figure, 64 is a hollow-structured cylinder to which the ball screw 40 is screwed, and 65 is a hollow-structured cylinder arranged concentrically with the cylinder 64.
The nut portion 20A in FIG. 8 is constituted by 4,65,
The arm 31 of the table 30 is integrally connected to the end of the cylinder 65. Here, the cylinders 64 and 65 act as a mover in the fail-safe system with respect to the table 30, which is a moving body.

A piston 66 having a hollow structure is provided in each of the cylinders 64 and 65, and oil is filled between the piston 66 and the cylinders 64 and 65 as shown in the drawing. This oil then reaches the external accumulator 62 shown in FIG. Further, 67 is an arm made of a magnetic material connected to the piston 66, and an inductive proximity switch 68 with a built-in coil, which is indirectly fixed to each of the cylinders 64 and 65, is arranged so as to face the arm 67. There is.

In this actuator 59, the rotation of the ball screw 40 applies a force to the table 30 via the cylinder 65, and when the reaction force exceeds the value set by the accumulator 62, the fail-safe system operates and the piston 66 relatively moves. To the left of. As a result, the distance between the arm 67 made of a magnetic material and the inductive proximity switch 68 is increased, so that the table 30 as a moving body receives an electric signal from the inductive proximity switch 68 that a force larger than the set value is applied. You can take it out.

In the actuator 59, the cylinder 65 is substantially stationary relative to the table 30 that moves linearly, and the axial force measurement according to the present invention is performed at a position substantially similar to the nut portion 20 of FIGS. 1 and 2. It is possible to build a load cell for the device. That is, as shown in FIG.
A wide groove 72 is formed in the central portion of the outer peripheral surface of the, and a narrow groove 73 is formed in the central portion of the inner peripheral surface. Then, on the bottom surface of the groove 72, strain gauges 74 are fixed respectively at positions that divide the outer peripheral surface thereof, and inside the groove 72, a silicone rubber 76 having a small foaming property or elasticity and an oil resistant silicone rubber 77 are filled. There is. Further, a thin portion 75 is formed between the groove 72 and the groove 73, and each of the above components constitutes a load cell as a whole.

Also in this example, the thin portion 75 of the load cell is distorted in response to the force of the table 30 that moves linearly in the X-axis direction, and an electric signal proportional to the axial force can be obtained from the strain gauge 74, and a substantially static system can be used. The axial force of the table 30 can be measured. In particular, in this example, based on the axial force thus measured, the force set value by the accumulator 62, that is, the force set value at which the fail-safe system operates can be changed in real time, and a fail that always has an optimum operation set value. A safe system can be realized.

Further, in this example, the load cell may be provided at the c portion of the piston 66 or the d portion of the cylinder 64 in FIG.

The present invention is not limited to the above-mentioned embodiment, but can be applied to the axial force measurement of various moving bodies which are linearly moved by being driven by a ball screw and a nut portion. Further, the present invention is
It can be applied to a system that measures the axial force of machines such as machine tools, and interlocks them in real time to adaptively control the feed and rotation of moving bodies.

(Effect of the invention) As described above, according to the present invention, the axial force of a moving body that moves linearly is seen from the thin portion of the nut portion and the force sensor that form a substantially stationary system when viewed relatively to the moving body. Since it is detected by the load cell, it is possible to accurately measure the axial force of the moving body without being disturbed by the movement of the drive source such as the motor or the power transmission mechanism such as the gear existing on the moving body side. .

Moreover, since the structure of the load cell itself is extremely simple,
The axial force measuring device according to the present invention can be provided at low cost.

Furthermore, this load cell can be built in advance in the nut part of the ball screw of the machine tool, eliminating the need to install a 6-minute force table etc. each time for axial force measurement as in the past. It is also possible to measure the axial force of a large load. At the same time, the axial force can be measured in parallel with the machining operation by the machine tool, so the machining conditions etc. can be changed quickly according to the measured axial force, realizing a highly efficient and highly accurate machining system. can do.

In addition, by using the present invention, it is possible to accumulate the force data of the moving body under a certain machining condition, and analyze it with an NC computer or the like to predict the tool life, damage, breakage, etc. Can be done. That is, by utilizing these accumulated data, the machine tool itself can automatically select and set the optimum machining conditions, and the machine tool can have a so-called self-learning function.

[Brief description of drawings]

FIG. 1 is an explanatory view of essential parts of an embodiment of the present invention, FIG. 2 is an enlarged explanatory view of part b of FIG. 1, FIG. 3 is an explanatory view of essential parts of an application example of the present invention, and FIG. Explanatory drawing of sensor color, Fig. 5 is No. 4
FIG. 6 is an enlarged explanatory view of part a, FIG. 6 is a model diagram of a spring system equivalent to FIG. 3, FIG. 7 is a force-displacement characteristic diagram of FIG.
FIG. 8 is a schematic configuration diagram of the machining center, and FIG. 9 is a sectional view of the actuator. 1 …… spindle, 7 …… housing 10 …… axial force sensor collar, 12,13,22,23,72,73 …… groove 14,24,74 …… strain gauge, 15,25,75 …… thin-walled part 20,20A …… Nut part, 30 …… Table 40 …… Ball screw, 59 …… Actuator 64,65 …… Cylinder

Claims (1)

[Claims] 1. A load cell is constructed by forming a thin portion on a nut portion of a ball screw that drives a linear motion body in a machine tool and fixing a force sensor to the thin portion to move along the axial direction of the ball screw. An axial force measuring device characterized in that the force sensor detects a reaction force from a linear moving body based on a strain generated in a thin portion.