阅读说明：本技术 用于调节切割机工具头中的刀口偏移量的设备 (Apparatus for adjusting the amount of knife edge offset in a cutter tool head ) 是由 达瑞尔·C·斯坦因 蒂莫西·菲利普·麦克唐纳 于 2020-12-17 设计创作，主要内容包括：一种用于调节具有切割机工具头框架的切割机工具头中的刀口偏移量的设备。该设备包括：刀具,该刀具可移动地耦接到工具头部；致动臂,该致动臂可移动地附接至切割机工具头部框架；计算机控制器,该计算机控制器用于控制所述刀具和致动臂的移动；研磨磨削器,该研磨磨削器可移动地附接至所述致动臂并且被适配成接触刀具；以及传感器,该传感器被适配成确定切割机工具头框架和致动臂之间的距离。设备的计算机控制器还能够根据由传感器确定的距离调节刀具和致动臂的运动。(An apparatus for adjusting the amount of knife edge offset in a cutter tool head having a cutter tool head frame. The apparatus comprises: a cutter movably coupled to the tool head; an actuator arm movably attached to the cutter tool head frame; a computer controller for controlling movement of the tool and the actuator arm; an abrasive sharpener movably attached to the actuator arm and adapted to contact a tool; and a sensor adapted to determine a distance between the cutter head frame and the actuator arm. The computer controller of the apparatus is also capable of adjusting the movement of the tool and the actuator arm according to the distance determined by the sensor.)

1. An apparatus for adjusting the amount of knife edge offset in a cutter tool head, comprising:

a cutter head frame;

a cutter movably coupled to the cutter head;

an actuator arm movably attached to the cutter head frame;

a computer controller that controls movement of the tool and the actuator arm;

an abrasive sharpener movably attached to the actuator arm and adapted to contact the tool; and

a sensor adapted to determine a distance between the cutter head frame and the actuator arm;

wherein the computer controller regulates movement of the tool and the actuator arm as a function of the distance determined by the sensor.

2. The apparatus of claim 1 wherein the cutter is a reciprocating cutter and the grinder comprises two grinding wheels.

3. The apparatus of claim 2, wherein the two grinding wheels comprise a first grinding wheel and a second grinding wheel configured to act as probes in contact with the tool.

4. The apparatus of claim 1, wherein the computer controller adjusts movement of the cutter and the actuator arm to compensate for knife edge wear.

5. The apparatus of claim 1, wherein said computer controller determines when said tool needs to be replaced.

6. The apparatus of claim 1 wherein said computer controller adjusts the aggressiveness of said abrasive sharpener to provide consistent material removal from said tool.

7. An apparatus for adjusting the amount of knife edge offset in a cutter tool head, comprising:

a cutter head frame;

a cutter movably coupled to the cutter head;

an actuator arm movably attached to the cutter head frame;

a computer controller that controls movement of the tool and the actuator arm;

an abrasive sharpener movably attached to the actuator arm and adapted to contact the tool; and

a sensor adapted to determine a distance between the cutter head frame and the actuator arm;

wherein the computer controller regulates movement of the tool and the actuator arm according to the distance determined by the sensor;

wherein the computer controller determines when the tool needs to be replaced; and

wherein determining whether the tool needs to be replaced comprises comparing a calculated knife edge offset from an average sensor output to a threshold.

8. The apparatus of claim 7, wherein the sensor generates an electrical signal that is directly related to the magnitude of the distance between the cutter head frame and the actuator arm, and the sensor is further adapted to measure the angle between the frame and the actuator arm.

9. The apparatus of claim 7, wherein the cutter is a reciprocating cutter and the grinder comprises two grinding wheels;

wherein the two grinding wheels comprise a first grinding wheel and a second grinding wheel configured to act as a probe in contact with the tool; and

wherein the first and second grinding wheels grind the tool when in an engaged position.

10. The apparatus of claim 9, wherein the first and second grinding wheels are stored when in a disengaged position.

11. The apparatus of claim 1, wherein the computer controller determines when a new tool is installed.

Technical Field

The present invention relates to Computer Numerical Control (CNC) machines that use a tool as a cutting tool for cutting shapes of flexible materials. More particularly, the present invention relates to Computer Numerically Controlled (CNC) machines that use a tool as a cutting tool and include sensors for determining tool offset to reduce cutting errors.

Background

Computer Numerical Control (CNC) machines may use a cutter as a cutting tool for automatically cutting shapes that are typically formed from flexible materials, such as fabrics and the like. A well-known use of such machines is to automatically cut garment components from a stack of fabric layers. Typically, the tool reciprocates in a direction parallel to the knife edge, and the tool is periodically ground by an automatic grinder built into the machine. Continued grinding wears the knife edge rearwardly, causing the position of the edge to shift from the ideal or original edge position. It is not uncommon for the knife edge to wear back 2.5 millimeters or more from its leading edge. Accurate CNC cutting must compensate for this offset of the knife edge. This is similar to a known method called cutter diameter compensation, where the programmed path input to the CNC machine is modified to account for the difference in cutter diameter from the nominal diameter. However, as discussed herein, the cutting tool is a cutter rather than a cylindrical cutting tool, such as an end mill or the like.

FIG. 1 illustrates a profile or tool path of an exemplary part suitable for CNC cutting using a tool. The contour includes a notch 101, the notch 101 being a common feature of the garment components and being used by a sewing machine operator as an alignment point between adjacent sewing components. An adverse effect of uncompensated edge offset is that the cutting feature (such as a notch, etc.) is displaced from its intended position. For example, the actual cutting notch 102 is shown displaced from the cutter path position of the notch 101. The cutting direction of the example of fig. 1 is counter-clockwise, which is in the direction indicated by arrow 100. The magnitude of the displacement follows the knife edge offset primarily geometrically.

The most common method of controlling the adverse effects of edge offset is to replace the tool before wear due to grinding exceeds a certain threshold amount. This method does not compensate for the offset, but it limits the amount of error. Other methods known in the art compensate for the knife edge offset. These methods require estimation or measurement of the knife edge position. One solution estimates the knife edge offset by tracking the number of grinds and using the count to predict the amount of wear. The accuracy of the method depends on the accuracy and knowledge of the relationship between the amount of grinding and the amount of wear. This relationship is complicated because as the grinder grit is used, the grinder grit becomes less aggressive, and thus the rate at which the grit wears the tool backwards decreases as the grit is used. This method also requires resetting the grinding counter when a new tool is installed, and this may be a manual operation subject to human error. The operator may forget or not know to reset the counter.

The prior art also includes methods for measuring knife edge offset using non-contact sensors. For example, U.S. patent publication No. 2015/0082957 (the disclosure of which is incorporated herein in its entirety) teaches a non-contact proximity sensor for measuring knife edge offset. The position of the edge is found without touching the knife. The use of non-contact methods in the prior art is motivated by the difficulty of measuring the position of the reciprocating edge by direct contact with the probe. The disclosed invention overcomes this difficulty by using the grinder wheel as a contact probe.

In the prior art, the tool grinding cycle has fixed parameters including contact pressure and duration of contact between the abrasive and the tool. As mentioned, the grinder grinding media becomes less aggressive when in use. Thus, the amount of edge wear depends on the erosion state of the grinding media. When the grinding media is new and aggressive, the grinding cycle tends to wear away excess material from the tool.

Accordingly, there is a need in the art for an apparatus that accurately determines the amount of knife edge offset for a cutter tool head. Further, there is a need in the art for an apparatus for preventing removal of excess material from the edge during grinding by adjusting the contact duration, grinding wheel speed, or pressure as needed to achieve uniform material removal from the tool for each grind.

Disclosure of Invention

It is therefore an object of the present invention to provide a sensor for measuring the size of the gap between the frame and the arm of a cutter tool head. The sensor generates an electrical signal that is directly related to the size of the gap. The size of the gap is directly related to the amount of knife edge offset of the knife used for the cutter tool head.

It is another object of the present invention to provide a first grinding wheel and a second grinding wheel that function as probes for contact with the cutters of a cutter tool head and mechanically control the size of the gap between the frame and the arm of the cutter tool head. Alternative sensors include capacitive proximity sensors, linear voltage displacement transducers, resistive potentiometers, encoders or any sensor that can generate a computer readable electrical signal related to the relative distance between two surfaces.

It is another object of the present invention to provide a knife edge offset that can be determined by a computer controller using data from a sensor that measures the size of the gap between the frame of the knife tool head and the arm. The sensor data is read by the computer controller when the first abrasive wheel and the second abrasive wheel are in contact with the tool of the tool head. The sensor data may be read or sampled multiple times over the duration of the grinding cycle at a rate to obtain a stored sample set. The knife edge offset is obtained from the averaged sensor data by a linear function, a table lookup calculation, or other functional mapping typically done by a computer controller.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention.

FIG. 1 illustrates a profile or tool path of an exemplary part suitable for CNC cutting using a tool.

Figure 2 shows a cutter tool head with a sensor for measuring the position of the knife edge according to the invention.

Fig. 3 shows a cutter tool head with a grinding wheel engaged with a cutter.

Figure 4 shows a cutter tool head with a grinding wheel disengaged from the cutter.

Detailed Description

The present invention is generally applicable to computer controlled machines that cut two-dimensional shapes on a planar work surface. The machine includes a gantry that positions the cutter tool head using two or more servo motors to follow a controlled tool path in a plane parallel to the work surface. The material to be cut is placed on the work surface. U.S. patent No. 4,205,835, the disclosure of which is incorporated herein in its entirety, describes a bristle bed working surface suitable for supporting material while being cut with a reciprocating knife.

Fig. 2 shows a cutter head comprising a cutter 10 driven by a cutter motor 16 to reciprocate perpendicular to a work surface and a drive means comprising a crank arm 17. The knife motor 16 provides the majority of the work done to cut the material. The tool 10 and the tool drive means including the crank arm 17 can be positioned in the tool up or tool down state by a lifting platform 19, which lifting platform 19 is typically actuated by an air cylinder. In the tool-down state, the tool 10 pierces and cuts material placed on a flat work surface. In the tool up state the tool 10 is in a safety plane above the material and in this state the tool can be moved to the starting point of the cutting line. The tool up position is also used to position the tool 10 for grinding. Fig. 2 shows the tool in a tool up state.

As illustrated in fig. 3, the tool 10 is periodically ground by the first grinding wheel 11 and the second grinding wheel 12. The first grinding wheel 11 and the second grinding wheel 12 are rotatably coupled to an arm 13 and are both driven by a grinder motor by means of a transmission comprising a gear or a belt. In a preferred embodiment, the arm 13 rotates about the pivot 22 relative to the frame 26, and the arm 13 is rotationally actuated to either the engaged or disengaged position by a rotary cylinder 24. In the engaged position shown in fig. 3, the first grinding wheel 11 and the second grinding wheel 12 are in contact with the tool 10 to grind the tool 10.

In the disengaged position shown in fig. 4, the first grinding wheel 11 and the second grinding wheel 12 are stored away from the tool 10, and in this state cutting and other non-grinding operations take place.

A preferred embodiment of the present invention includes a sensor 20 attached to a frame 26, the sensor 20 attached to the frame 26 measuring the size of the gap 21 between the arm 13 and the frame 26. The sensor 20 generates an electrical signal that is directly related to the size of the gap 21 that can be read by a computer controlled machine. The size of the gap is directly related to the knife edge offset. That is, the first grinding wheel 11 and the second grinding wheel 12 serve as probes for contact with the tool 10 and mechanically manipulate the size of the gap 21. Alternative sensors include capacitive proximity sensors, linear voltage displacement transducers, resistive potentiometers, encoders or any sensor that can generate a computer readable electrical signal related to the relative distance between two surfaces. Another embodiment of the invention measures the angle between the arm 13 and the frame 26. The angle may be measured by a rotary encoder or other equivalent sensor that produces a computer readable electrical signal. Yet another embodiment of the present invention has an arm 13, the arm 13 being slidably coupled to the frame 26 rather than rotating about the pivot 22. For example, the arm 13 may be mounted to a linear bearing that will allow the first and second grinding wheels 11, 12 to slide along a line to create an engaged position where the tool 10 is ground and a disengaged position where the grinding wheels are stored. Actuation of the grinder may be achieved by a linear cylinder rather than a rotary cylinder 24.

The knife edge offset is determined by the computer controller using data from the sensor 20. When the first grinding wheel 11 and the second grinding wheel 12 are in contact with the tool 10, the sensor 20 output is read by the computer controller. The sensor 20 output may be read or sampled multiple times over the duration of the grinding cycle at a rate to obtain a stored sample set. Each sample may be slightly different due to vibration and electrical noise. If the rate is 100 samples per second and the grinding duration is 0.5 seconds, the sample set will include 50 stored values. This sample set can be averaged by the computer controller to obtain an average sensor output and is a less sensitive estimate of the effects of vibration and electrical noise. The knife edge offset is obtained from the average sensor output by a linear function, a table lookup calculation, or other functional mapping typically done by a computer controller.

In a preferred embodiment, the knife edge offset is calculated from the average sensor output using a linear function. Preferably, the knife offset is nominally zero for a new tool and increases as the tool 10 wears. The slope of the linear function may be such that a knife edge offset in standard size units (such as millimeters, etc.) is obtained. In a preferred embodiment, the knife edge offset is further processed by a computer controller. Each grinding cycle will produce a new edge offset value. Due to vibration and electrical noise, there will in fact be some variation in the sequence of values. Those skilled in the art will recognize that a smoother estimate may be obtained by calculating a weighted average of the current and some previous edge offset values. In a preferred embodiment, this estimate will replace the original knife edge offset.

The information of the knife edge offset can be used by the computer controller to compensate for the worn knife edge. For example, without compensation, the tool path position of the notch 101 in fig. 1 is shifted to the position of the actual cutting notch 102. The computer controller executes a compensation algorithm that modifies the tool path geometry such that the actual edge follows the tool path. Solutions to this problem are well known to those skilled in the art of inverse kinematics.

Another use of the knife edge offset is for automatically determining when the tool 10 needs to be replaced. After each grind, the computer controller may compare the amount of edge offset to a threshold. The machine may alert the operator or stop the machine and if the knife edge offset exceeds a threshold, the tool 10 needs to be replaced.

Yet another use of the knife edge offset is for automatically determining when a new knife is installed. The computer controller can detect a new tool by looking for the edge offset to drop to near zero after previously maintaining a much larger value. The information about when the tool is new and when it needs to be replaced makes it possible for the computer controller to count the number of grindings a particular tool receives over its course of life and to inform the operator of the necessary tool changes waiting or to stop operation when the tool has worn to its useful life.

Yet another use of the knife edge offset is to determine an aggressiveness estimate for the first and second grinding wheels, and use the aggressiveness estimate to adjust grinder cycle parameters (such as grinding time, etc.) to achieve consistent material removal from the tool in a single grind. The aggressiveness estimate can be calculated as the change in the amount of lip offset for each grinding wheel revolution. Preferably, the aggressiveness estimate will be calculated as the average of multiple grinds, such as the last 100 lapping cycles. It is desirable to maintain the cycle parameters of the grinder so that the change in the amount of edge offset per grind is almost always equal to the target value. For example, the target value may be 0.8 microns per grind. The computer controller will use the aggressiveness estimation information in a feedback loop that adjusts the grinding time or grinding cycle of the grinding wheel speed. The reduced aggressiveness estimate may be compensated for by increasing one or both of the grinding time or the grinding wheel speed. Either compensation increases the number of revolutions of the grinding wheel per grind, thereby increasing the material removal per grind.

The computer controller may use the aggressiveness estimate to detect when the first grinding wheel and the second grinding wheel need to be replaced. The aggressiveness estimate will decrease slowly as the grinding wheel ages. Eventually, the aggressiveness estimate will drop to too low a level where it is no longer practical to compensate for the reduction in blade material removal by increasing the grinding time or grinding wheel speed. The computer controller may monitor the aggressiveness estimate and when the estimate falls below a threshold, will notify or force the operator to change the first grinding wheel 11 and the second grinding wheel 12.

It will be appreciated that abrasive wear of the first and second grinding wheels 11, 12 will contribute to the reading of the sensor 20. However, abrasive wear is assumed to be small and negligible relative to tool wear. More specifically, the grinding wheel 11 and the second grinding wheel 12 are preferably Cubic Boron Nitride (CBN). Cubic boron nitride grinding wheel 151 microns (0.0059 inch) grain size. About 55% of these particles are encapsulated to mechanically hold them to the wheel. Thus, the abrasive wear contributes only 45% or 68 microns (0.0027 inches) of the grain size to the sensor 20 reading. These values are negligible when compared to the 2500 micron (0.10 inch) possible tool wear.

The present invention in its broader aspects is not limited to the specific embodiments shown and described herein, and, therefore, may be varied within the scope of the appended claims without departing from the principles of the invention and without sacrificing its material advantages.