MARKER HEAD WITH PRESSURE SENSOR

Description

[0001] The invention relates to a method according to the preamble of claim 1.

[0002] Various material-displacing marking systems are known for marking workpieces.

[0003] Among other things, marking systems are known in which the marking is carried out with an oscillating, pointed, hard needle that can move along at least two coordinates and thereby marks alphanumeric characters and free symbols such as QR codes, company logos, etc., onto a surface. The principle is like that of a dot matrix printer, except that the pointed, oscillating needle presses many points next to each other into the material surface, making the marking visible.

[0004] A disadvantage is that if interference occurs, a marking process might not actually take place. While the XY coordinate paths of the marking points can be monitored, this does not guarantee that the marking has actually occurred.

[0005] Patent 10 2006 056 388 B3 discloses a device for marking a workpiece with a marking tool which can be guided along a marking path specified by a control device by means of an actuator, to which device a marking test unit is assigned which captures at least a first and second process parameter and generates a corresponding first and second test signal.

[0006] US patent 2016 / 0108487 A1 discloses a pneumatic needle roller with two needles, wherein each of the needles is driven by the pressure in a piston chamber and the needles interact with a control valve that disconnects the piston chamber from the pressure supply when the needle is extended and connects it to the pressure supply when the needle is retracted.

[0007] On the downside, the systems are complex and prone to malfunctions.

[0008] German patent application DE 20 2008 017 427 U1 discloses a device for producing a mark on a workpiece surface by embossing. A distance sensor is attached to the embossing needle, which determines the embossing depth during the process. The distance sensor must be designed to move quickly with the embossing needle and is therefore subject to high loads and prone to wear. The device requires relatively intensive maintenance.

[0009] It is therefore an object of the present invention to provide a method that enables simple verification of a marking by a marking head.

[0010] The problem is solved by a method for verifying a marking with the features of claim 1 as mentioned above.

[0011] In the method according to the invention, compressed air is continuously supplied to a piston, preferably a needle piston, oscillating in a needle head housing of a marking head. The oscillating needle piston has a needle at one end that inserts markings into a surface.

[0012] During oscillation, pressure fluctuations occur in the compressed air supply. The pressure of the compressed air supply is continuously measured. A pressure profile is created and compared with a reference pressure profile stored in an evaluation unit for analysis.

[0013] Advantageously, this provides a method that is less susceptible to interference and requires minimal design modifications compared to existing marking heads. A pressure sensor is integrated into the compressed air supply. The pressure values ​​measured by the sensor are recorded and evaluated. The pressure sensor should be very fast and capable of detecting pressure fluctuation frequencies of up to approximately 10 kHz or even higher.

[0014] The pressure measurements are recorded or stored and evaluated over time.

[0015] Preferably, the pressure profile of a freely oscillating needle is first measured and stored as a free reference pressure profile in the evaluation unit. This free reference pressure profile shows the pressure changes over time when the needle oscillates freely without ever penetrating the surface to make a mark. The frequency of the free reference pressure profile remains essentially the same, ideally constant, over time.

[0016] Additionally or instead, the pressure profile of a marking-producing needle can be measured and stored as a marking reference pressure profile in the evaluation unit. A marking-producing needle is defined as one that penetrates the surface with each oscillation, thus producing a perfect mark or at least a nearly perfect mark, and penetrates the surface in at least more than 90 percent, preferably more than 95 percent, of each oscillation. The marking reference pressure profile is stored in the evaluation unit.

[0017] During a marking process, the actual pressure profile is constantly measured. "Constantly measured" here means that enough pressure readings are taken to determine a continuous pressure curve, at least through interpolation or similar methods.

[0018] The pressure is measured by the pressure sensor and also fed to the evaluation unit. In the evaluation unit, the resulting pressure profile or pressure curve can be compared with the free reference pressure profile and / or with the marked reference pressure profile.

[0019] According to the invention, a frequency of the free reference pressure profile is determined, and a frequency of the pressure profile is continuously measured. The frequencies are compared, and an error message is generated if the frequency of the pressure profile is not lower than the frequency of the free pressure profile. When the needle oscillates freely, the associated needle piston has its maximum stroke, and the frequency is at its maximum for the same compressed air volume. When the needle penetrates the surface, the stroke is naturally shorter because the piston does not first strike a stop but impacts the surface beforehand, and the frequency increases. If the frequency of the pressure profile is not lower than the frequency of the free pressure profile, an error message is generated.In particular, an error message is generated if the frequencies of the two print profiles are the same, meaning that the comparison determines that the print profile corresponds to the free print profile, at least with regard to frequency, i.e., the needle is oscillating freely. At that moment, there is a marking error.

[0020] In another evaluation variant, the reference print profile is compared with the print profile, and an error message is generated if there are deviations. The comparison of the print profiles can be achieved by performing a Fourier analysis on both the print profile and the reference print profile, and then comparing the individual frequencies of the Fourier transforms.

[0021] Preferably, only a Fourier analysis of the pressure profile can be performed, and the occurrence of certain frequencies can be used to determine how worn the needle is, whether the surface hardness has changed, and other data.

[0022] Preferably, the needle oscillates back and forth in a Z-direction, and the oscillation imprints a mark onto the surface. According to the invention, the needle piston, on one side of which the needle is arranged, is pushed towards the surface by compressed air and pushed back by a spring force. The compressed air and spring force work together to generate the oscillating movement of the needle piston. During the oscillation, the compressed air flows longitudinally around the needle piston and then out of an outlet in the marking head. Only when the needle piston is fully retracted is it sealed by a stop seal, preventing air from flowing around it. At this moment, the compressed air exerts its maximum pressure on the needle piston and pushes it towards the surface in the Z-direction. The acceleration and the

[0023] The inertia of the needle piston causes the needle tip to penetrate the surface, creating the mark. This compresses the spring, and after the mark is made, the needle piston is pushed back to its fully retracted position by the relaxing spring.

[0024] The invention is described with reference to an exemplary embodiment in six figures. These show: Fig. 1 Sectional view of a marking head according to the invention, Fig. 2a Sectional view of the marking head according to the invention during a marking process, Fig. 2b Marking applied to a surface, Fig. 2c Pressure profile measured at a pressure sensor as a function of time, Fig. 3a Pressure marking button according to the invention with freely oscillating needle, Fig. 3b Pressure profile measured at a pressure sensor over time.

[0025] A marker head 1 in Fig. 1 The device comprises a needle piston 2 with a needle 3 arranged at a surface-side end of the needle piston 2. The needle 3 is made of, or incorporates, a high-strength material, such as hard metal or diamond, or at least has a diamond tip. The needle piston 2 has a T-shaped cross-section. The needle piston 2 has its greatest width along its head, which faces away from the surface 4 to be machined. However, it does not seal tightly against an inner wall 6 of a needle head housing 7, allowing air to flow between the needle piston 2 and the inner wall 6 of the needle head housing 7. The airflow is in Fig. 2a represented by arrows.

[0026] The needle 3 is intended for placing a mark 8 into the surface 4.

[0027] In a section facing away from surface 4, the needle head housing 7 is sealed against the needle piston 2 by a stop seal 9. The sealed area is connected to a compressed air supply 10. Compressed air is continuously introduced into the section of the needle head housing 7 facing away from surface 4 via the compressed air supply 10. A pressure sensor 11, capable of detecting pressure fluctuation frequencies up to 10 kHz, is arranged laterally on the compressed air supply 10. The pressure sensor 11 is electrically and data-conducting connected to an evaluation unit 12. The evaluation unit 12 records the pressure profile measured by the pressure sensor 11 over a period of time t in a memory.

[0028] On the surface side, a spring 13 is placed around a T-leg 14 of the needle piston 2. This spring exerts a counterforce to the compressed air and, in conjunction with the compressed air, causes the needle piston 2 to oscillate back and forth in a longitudinal direction L. The oscillations can range from 10 to 500 Hz, but depending on the design of the needle head 2, the frequencies can also be lower or even higher.

[0029] In the Fig. 1 In the fully retracted position of the needle 4 and the needle piston 2 shown, the end of the needle piston 2 furthest from the surface is sealed by the stop sealing ring 9. In this position, the compressed air flowing from the compressed air supply 10 exerts an impulse on the needle piston 2, and the needle piston 2 is accelerated towards the surface 4. The position on the way towards the surface is shown in the Fig. 2a The needle piston 2 has moved away from the stop sealing ring 9, and the compressed air can flow laterally past the needle piston 2 and escape from the needle head housing 7 into the surrounding environment in a surface-side section of the marking head 1. This causes the pressure of the compressed air in the non-surface section of the interior of the needle head housing 7 to collapse. The pressure sensor 11 experiences a change in the position shown. Fig. 1 In its fully retracted state, the needle piston generates a maximum impulse. As the needle piston 2 moves downwards, the pressure measured by the pressure sensor 11 decreases.

[0030] During the downward movement of the needle piston 2, the spring 13 is compressed, and the compressed spring 13 pushes the needle piston 2 back in the other direction, thereby increasing the pressure at the pressure sensor 11.

[0031] This creates a rapidly oscillating movement of the needle 3, which is used to introduce the marking 8 into the surface 4. The movement of the needle 3 occurs in the longitudinal direction L, which here corresponds to a Z-direction, while the marking head 1 is moved in an XY plane by a controller, for example a CN controller or similar, and the needle 3 marks free symbols such as QR codes, company logos, etc., onto the surface 4. Fig. 2b The marker 8 is chosen in the form of the number "78".

[0032] During the downward movement of the needle 3 in the Z-direction towards the surface 4, the movement is naturally stopped when the needle tip hits the surface 4, and the spring 13 immediately pushes the needle piston 2 back up, away from the surface 4. This position is in Fig. 2a depicted.

[0033] The closer the surface 4 is positioned to the marking head 1, the smaller the stroke of a stroke movement of the needle piston 2 becomes, and thus the frequency of the back-and-forth movement of the needle 3 increases, or in other words, the duration of an oscillation period increases.

[0034] When the needle 3 hits the surface 4, thus the movement is suddenly interrupted, the pressure sensor 11 measures specific impulses, which are exemplified in Fig. 2c are shown in the valleys of the otherwise essentially sinusoidal pressure curve.

[0035] In the Fig. 2c A marking pressure profile is shown. The valleys of the pressure profile also provide information about the wear of the needle tip, the surface strength, and the penetration depth of the needle tip into the surface. 4. An analysis of the marking pressure profile can be obtained by Fourier analysis of the pressure profile, which, however, is not shown.

[0036] In the Fig. 3a and 3b The same marking head 1 with oscillating needle piston 2 is shown, but without a surface 4. The needle piston 2 oscillates freely, and it is shown in Fig. 3b A free reference pressure profile was measured. Because the stroke of needle piston 2 during a free oscillation is greater than the stroke of needle piston 2 during a marking oscillation, the frequency will be smaller; therefore, the duration T1 of one period of the free reference pressure profile will be greater than the duration T2 of one period of the marking pressure profile.

[0037] Furthermore, due to contact with surface 4, a curve profile emerges in the valleys of the pressure profile, which also deviates from the curve profile of the marking pressure profile.

[0038] The pressure sensor 11 and the evaluation unit 12 connected to it are intended to determine whether the needle 3 actually makes the mark 8 on the surface 4 during oscillation or vibration, or whether the needle 3 is possibly oscillating freely, jammed, or something similar, i.e., not making a mark 8 on the surface 4. For this purpose, the Fig. 3b The pre-measured free reference pressure profile is stored in a memory of the evaluation unit 12.

[0039] The free reference pressure profile according to Fig. 3b This provides information about the pressure profile of the marking head 1 in its current state when the needle 3 oscillates freely and does not make a mark 8 on the surface 4. During the marking process, according to Fig. 2a The pressure is continuously measured by pressure sensor 11 and fed to the evaluation unit 12. The marking pressure profile can be stored, or at least temporarily. The marking pressure profile must constantly and continuously differ from the free reference pressure profile, especially in the troughs. Should the needle 3 oscillate freely for some periods or even just one period, for example because the surface 4 is too far from the needle 3, the marking pressure profile will no longer be valid. Fig. 2c the same shape, or essentially the same shape, as the free reference pressure profile of the Fig. 3b By comparing the two print profiles, the exact time intervals during which the needle 3 oscillates freely and does not make a mark 8 on the surface 4 can be determined. An error signal is then generated, the marking 8 is aborted, or at least an indication is given that there is a malfunction in the marking process.

[0040] Furthermore, a marking reference pressure profile is also stored in the evaluation unit 12. This reference pressure profile is determined when a perfect or at least a nearly perfect marking 8 is performed, i.e., when every oscillation movement penetrates the surface 4. The marking pressure profile actually occurring during a marking process is preferably compared not only with the free reference pressure profile but also with the marking reference pressure profile. If the marking pressure profile deviates from the marking reference pressure profile, an error signal is also issued to indicate that an irregularity in the marking process has occurred. The markings 8 can then be automatically rejected, or at least an error message can be sent to the operating personnel. Bezugszeichenliste

[0041] 1 Marker head 2 Needle piston 3 Needle 4 Surface 6 Inner wall 7 Needle head housing 8 Marking 9 Stop sealing ring 10 Compressed air supply 11 Pressure sensor 12 Evaluation unit 13 Spring 14 T-leg Longitudinal direction tTime T1 duration T2 duration

Claims

1. Method for verifying a marking (8), wherein compressed air is supplied to a section of a needle head housing (7) of a marking head (1) facing away from a surface (4), in which a needle piston (2) oscillates, which has a needle (3) at one end that inserts the marking (8) into the surface (4), whereby pressure fluctuations are formed in a compressed air supply line (10) during the oscillation, the air pressure in the compressed air supply line (10) is continuously measured, the needle piston (2) oscillates back and forth in a Z direction and the needle (3) embosses the marking (8) into the surface (4) by the oscillation (4) and the needle piston (2) is pressed against the surface (4) by the compressed air, thereby compressing a spring (13), and is pushed back by the relaxing spring (13), characterised in that compressed air is continuously supplied to the section of the needle head housing (7) facing away from the surface (4), wherein the needle head housing (7) is sealed against the needle piston (2) by means of a gasket ring (9) and a sealed area is connected to a compressed air supply line (10) in such a way that air can pass through, air pressure is continuously measured by a pressure sensor (11) arranged in the compressed air supply line (10), a pressure profile is created and compared with a reference pressure profile stored in an evaluation unit (12) and evaluated, the compressed air flows around the needle piston (2) out of an outlet from the needle piston housing (7) of the marking head (1) during oscillation, and in a maximum retracted position, a gasket ring (9) prevents the compressed air from flowing past the needle piston (2).

2. Method according to claim 1, characterised in that a pressure curve of the freely oscillating needle (3) is measured and stored as a free reference pressure profile in the evaluation unit (12).

3. Method according to claim 1 or 2, characterised in that the pressure curve of the needle (3) producing the marking (8) is measured and stored as a marking reference pressure profile in the evaluation unit (12).

4. Method according to claim 1, 2 or 3, characterised in that a frequency of the free reference pressure profile is determined and a frequency of the pressure profile is continuously measured and the frequencies are compared with each other and an error message is generated if the frequency of the pressure profile is not smaller than the frequency of the free pressure profile.

5. Method according to one of claims 1 to 4, characterised in that the marking reference pressure profile is compared with the pressure profile and an error message is generated in the event of deviations.