Dynamically dampened centerless grinding machine tool and grinding method

Abstract

The invention relates to a dynamically dampened centerless grinding machine tool comprising wheels between which there is arranged a part to be ground, heads for carrying the wheels, at least one translation means for translating one of the heads to cause a movement according to a separation and approach direction of the wheels, detection means for detecting a vibration of at least one of the heads, and at least one damper configured for causing a vibration damping movement.

Claims

1. A dynamically dampened centerless grinding machine tool comprising: a grinding wheel and a control wheel between which there is arranged a part to be ground; two heads for carrying the wheels; at least one translation means for translating one of the heads to cause a movement according to a separation and approach direction in a longitudinal direction of the wheels; detection means for detecting a vibration of at least one of the heads; at least one damper configured for causing a vibration damping movement, wherein the at least one damper is on top of an uppermost surface of one of the two heads, the damper comprising a moving mass and an actuator configured to move the moving mass in the separation and approach direction in the longitudinal direction of the wheels.

2. The dynamically dampened centerless grinding machine tool according to claim 1, wherein there are two dampers, one for each of the heads, one of the dampers being configured for causing the vibration damping movement of one of the heads, and the other one of the dampers being configured for causing the vibration damping movement of the other one of the heads.

3. The dynamically dampened centerless grinding machine tool according to claim 1, wherein there are two detection means, one of the detection means being configured for detecting the vibration of one of the heads, and the other one of the detection means being configured for detecting the vibration of the other one of the heads.

4. The dynamically dampened centerless grinding machine tool according to claim 1, wherein the at least one damper is configured for generating the damping movement that is opposite the vibration, as detected by the detecting means.

5. The dynamically dampened centerless grinding machine tool according to claim 1, wherein the at least one damper is configured for generating the damping movement in the separation and approach in the longitudinal direction of the wheels.

6. The dynamically dampened centerless grinding machine tool according to claim 1, wherein the damper is arranged in the center of the uppermost surface of the head.

7. The dynamically dampened centerless grinding machine tool according to claim 6, wherein the damper is arranged at an end of the uppermost surface that is closest to a holding means for holding the part.

8. The dynamically dampened centerless grinding machine tool according to claim 1, wherein the detection means detecting the vibration of one of the heads and the damper causing the vibration damping movement are arranged in the same head.

9. A grinding method comprising the dynamically dampened centerless grinding machine tool according to claim 1, comprising the steps of: arranging the detection means and the damper in the centerless grinding machine tool; detecting the vibration of at least one head of the machine using the detection means; and causing the vibration damping movement by means of the damper.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a centerless grinding machine tool with a basic setup according to the state of the art.

(2) FIGS. 2 and 3 show a schematic view of the two main vibration modes of a centerless grinding machine tool, such as that depicted in FIG. 1.

(3) FIG. 4 shows a first embodiment of a centerless grinding machine tool according to the invention with a stationary head and another head arranged in translation means.

(4) FIG. 5 shows a second embodiment of a centerless grinding machine tool according to the invention with both heads arranged in respective translation means, wherein the damper is arranged in the head of the regulating wheel.

(5) FIG. 6 shows the machine of the second embodiment with the damper arranged in the head of the grinding wheel.

(6) FIG. 7 shows the machine of the second embodiment with a damper arranged in each head of the machine.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a centerless grinding machine with a basic setup according to the prior art. The grinding machine comprises two wheels (1, 2), a grinding wheel (1) and a regulating wheel (2), between which there is arranged a part (3) to be ground supported on holding means (4). Each wheel (1, 2) is arranged in a head (5, 6), wherein at least one of the heads (5, 6) is arranged on translation means (8), such that by means of the movement of the translation means (8) a separation and approach movement of the wheels (1, 2) occurs. Said movement occurs in the direction depicted in the drawings by means of the arrow (F) and is perpendicular to the blade (4) and therefore to the longitudinal axis of the part (3).

(8) Accordingly, in operation the regulating wheel (2) is taken by the translation means (8), applying pressure on the part (3) in the direction of movement of the translation means (8), depicted by the arrow (F), such that the part (3) is retained between the wheels (1, 2), being supported such that it freely rotates on the holding means (4), so the part (3) is ground by means of the rotation of the wheels (1, 2).

(9) Grinding creates forces which cause the excitation of the vibration modes of the different components of the machine, such as the heads (5, 6), which generates vibrations that are transmitted to the machining point located in the contact area between the part (3) and the wheels (1, 2). This causes geometric defects or excessive wear of the machining tool, or a poor surface finish of the part (3), among other factors. As can be seen in FIGS. 2 and 3, the centerless grinding machine has two main vibration modes which cause the heads (5, 6) to bend, resulting in them moving farther away or closer, depending on the direction of rotation of the wheels (1, 2).

(10) According to the invention, a centerless grinding machine is proposed which allows detecting vibrations occurring in the contact area between the part (3) and the wheels (1, 2) acting on them to suppress them, such that the surface finish of the parts is improved, machine productivity increased and the life of its components prolonged.

(11) According to the foregoing, the invention proposes a machine tool such as the one described in FIG. 1 and which additionally comprises detection means (9) for detecting a vibration of at least one of the heads (5, 6) and at least one damper (10) configured for causing a vibration damping movement for damping the detected vibration.

(12) The detection means (9) and the damper (10) are preferably arranged in one and the same head (5, 6). In other words, the detection means (9) and the damper (10) are located in approximately the same point, such that action is taken at the same point in which the occurrence of the vibration is detected. The phase of the force introduced by the damper (10) is thereby assured to be such that it is opposite the vibration in all the vibration modes that may occur.

(13) Furthermore, since the damper (10) is arranged in the head (5, 6), action is taken near the source of the vibration, i.e., the contact point between part (3) and the wheels (1, 2), and furthermore action is taken directly on the head (5, 6) itself, which is the member of the machine that is directly exposed to the vibration, since it is the member carrying the wheels (1, 2).

(14) As shown in the embodiment of FIG. 4, the machine has the detection means (9) and the damper (10) arranged in the head (6) which is arranged on the translation means (8), although the detection means (9) and the damper (10) could be arranged in the head (5) which is fixed to the frame of the machine.

(15) Alternatively, the machine depicted in the embodiment of FIG. 4 can have two detection means (9) and two dampers (10), such that the first detection means (9) and the first damper (10) are arranged in the head (5) of the first wheel (1), the grinding wheel (1), and the second detection means (9) and the first damper (10) are arranged in the head (6) of the second wheel (2), the regulating wheel (2), which is arranged on the translation means (8).

(16) In any case, although the detection means (9) and the damper (10) are preferably arranged in one and the same head (5, 6); this option is not a limiting option, as it is possible for the detection means (9) and the damper (10) to be arranged at other points of the machine. For example, the detection means (9) could be arranged in the head (6) which is mounted on the translation means (8), and the damper (10) could be arranged on the translation means (8); nevertheless, in that case a greater force would be required to dampen the vibration, since action would be taken at a point farther away from the source of the vibrations, and additionally the damping would be less efficient since action would be taken at a point other than the point where measurement would be taken.

(17) FIGS. 5 to 7 show a second embodiment of the invention, which is identical to the first embodiment with the difference being the existence of two translation means (7, 8), one for each of the wheels (1, 2), a first translation means (7) of the first wheel (1), and a second translation means (8) of the second wheel (2). Both translation means (7, 8) move the heads (5, 6) in the direction depicted in the drawings by means of the arrow (F), which is perpendicular to the blade (4) and therefore to the longitudinal axis of the part (3).

(18) FIG. 5 shows a centerless grinding machine according to the second embodiment of the invention with the detection means (9) and the damper (10) arranged in the first head (5) of the first translation means (7).

(19) FIG. 6 shows a centerless grinding machine according to the second embodiment of the invention with the detection means (9) and the damper (10) arranged in the second head (6) of the second translation means (8).

(20) FIG. 7 shows a centerless grinding machine according to the second embodiment of the invention with first detection means (9) and a first damper (10) arranged in the first head (5) of the first translation means (7) and with second detection means (9) and a second damper (10) arranged in the second head (6) of the second translation means (8). Better attenuation of the vibrations is achieved with this embodiment, because since the wheels (1, 2) are in contact through the part (3) during grinding, vibrations are transmitted to both heads (5, 6), whereby the arrangement of one pair of detection means (9) and damper (10) per head (5, 6) to dampen vibrations occurring in both heads (1, 2) is advantageous.

(21) The damper (10) is an active damper comprising a moving mass and an actuator of the moving mass, such that it is coupled to a head (5, 6) in order to introduce therein a controlled force which is a function of the amplitude of the signal obtained by the detection means (9).

(22) The damper (10) has been envisaged to be a hydraulic, piezoelectric, or electromagnetic device, a linear motor or any other means suitable for introducing a controlled force.

(23) The damper (10) is preferably configured for generating the damping movement that is opposite the vibration.

(24) The damper (10) is preferably a one-way damper generating the damping movement in the direction of movement of the translation means (7, 8) depicted by the arrow (F). In other words, grinding causes a vibration in the direction in which the wheel (1, 2) applies pressure on the part (3) according to a relative movement for moving the translation means (5, 6) and the part (3) closer to/farther away from one another, such that the damper (10) generates a damping movement in said direction.

(25) Alternatively, the damper (10) is a two-way damper generating a first damping movement in the direction of movement of the translation means (7, 8), depicted by the arrow (F) in the drawings, and optionally a second damping movement in a direction perpendicular to the direction of movement of the translation means (7, 8) and parallel to the longitudinal axis of the part (3).

(26) The detection means (9) are preferably an accelerometer that measures the frequency and amplitude at which the head (5, 6) in which the accelerometer is arranged oscillates due to the machining process.

(27) Use of a passive damper comprising a moving mass but not an actuator of said moving mass would be possible in order to dampen vibration; however, the high value of the modal mass of the critical modes of the grinding machine makes the inertial mass to be introduced very large, so a passive damper with a very large moving mass would be required, and a lot more space would be required for arranging it. However, by using an active damper such as the one proposed by the invention, a smaller moving mass is required since a controlled force is applied on the moving mass according to the information sent by the detection means (9).

(28) The damper (10) is preferably arranged on an upper face (5.1, 6.1) of the head (5, 6), which is opposite the lower face where the head (5, 6) is attached to the translation means (7, 8), or where appropriate to the frame of the machine. Action is thereby taken on the area of the head (5, 6) that oscillates the most when vibrations occur.

(29) The damper (10) is even more preferably arranged in the center of the upper face (5.1, 6.1) of the head (5, 6), and even more preferably at an end of the upper face (5.1, 6.1) which is closest to the holding means (4) for holding the part (3), such that action is taken at the point of the head (5, 6) that is closest to the point of origin of the vibrations.

(30) A grinding method is thereby obtained, comprising the steps of arranging detection means (9) and a damper (10) in a centerless grinding machine tool, detecting a vibration of at least one head (5, 6) of the machine using the detection means (9), and causing a vibration damping movement by means of the damper (10).

(31) The detection means (9) allow knowing the frequency and amplitude at which the head (5, 6) vibrates in real time such that the frequency and force to be introduced by the damper (10) to suppress vibration can be adjusted, thereby assuring that vibrations will not occur during the operation for grinding the part (3).