Machine tool and method for operating a machine tool

Abstract

A machine tool and method for drilling holes or fastening screws, the machine tool comprising a motor having a shaft, supplying current to the motor to rotationally drive the shaft, continuously determining a set of parameters characterizing the drilling and / or fastening process, recognizing that the parameter state of each parameter of the set of parameters is constant when the change in the parameter over time is below a threshold value, recognizing that the parameter state of each parameter of the set of parameters is changing when the change in the parameter over time is above a threshold value, continuously determining the number of parameters whose parameter state is changing, and a controller configured to stop the motor when that number is at least a predefined minimum number over a predetermined time interval.

Description

Technical Field

[0001] Machine tools for making holes such as lower holes and / or fastening screws, and methods of operating the machine tools are described herein. Also described are handheld power tools that enable hole-making and / or screw-fastening operations. Generally, such handheld tools are widely used in the construction industry. Typical handheld tools within the technical scope of the present invention include, but are not limited to, automatic screwdrivers for screwing screws onto workpieces, thereby fastening workpieces such as metal plates with screws.

Background Art

[0002] Handheld power tools that enable screw fastening are known. This tool includes a machine tool housing that includes a motor that provides at least a rotational motion to a rotating shaft. The rotating shaft then finally transmits a specific torque at a specific rotational speed to a workpiece fastening element such as a drill or a screw tool. The tool may also include a controller for controlling the motor and continuously determining some parameters of the hole-making or fastening process, such as the transmitted torque and rotational speed of the rotating shaft, during use of the tool.

[0003] One possible application area is, for example, under-hole drilling as preparation for fastening self-tapping and self-sealing screws using a step drill. Such work is usually performed by professional construction workers who can press the step drill against the foundation structure with a large force over a long period of time to ensure that the under-hole is deep enough. Due to such a large force and long time, the shape of the under-hole may become inaccurate.

Summary of the Invention

Means for Solving the Problems

[0004] One aspect of the present invention is a method of operating a machine tool for drilling a hole in a workpiece and / or fastening a screw along a fastening axis, the machine tool including a motor having a shaft, the method comprising supplying an electric current to the motor to rotationally drive the shaft, continuously determining a set of parameters characterizing the drilling and / or fastening process, recognizing that the parameter state of each parameter of the set of parameters is constant when the change over time of the parameter is below a threshold value, recognizing that the parameter state of each parameter of the set of parameters is changing when the change over time of the parameter exceeds the threshold value, continuously determining the number of parameters whose parameter state is changing, and stopping the motor when that number is at least a predefined minimum number over a predefined time interval. The predefined minimum number can be 2, 3, 4, 5 or more. The predefined time interval can be 1 second, a fraction of a second or zero.

[0005] According to another aspect, a machine tool for drilling a hole in a workpiece and / or fastening a screw along a fastening axis includes a motor having a shaft, a switch, and a controller configured to supply an electric current to the motor to rotationally drive the shaft, continuously determine a set of parameters characterizing the drilling and / or fastening process, recognize that the parameter state of each parameter of the set of parameters is constant when the change over time of the parameter is below a threshold value, recognize that the parameter state of each parameter of the set of parameters is changing when the change over time of the parameter exceeds the threshold value, continuously determine the number of parameters whose parameter state is changing, and stop the motor when that number is at least a predefined minimum number over a predefined time interval. The predefined minimum number can be 2, 3, 4, 5 or more. The predefined time interval can be 1 second, a fraction of a second or zero.

[0006] According to one aspect of the present invention, the set of parameters includes at least one of a force applied to the shaft and directed towards the machine tool along the fastening axis, a torque applied to the shaft and centered on the fastening axis, a voltage of the current supplied to the motor, an ampere number of the current supplied to the motor, a rotational speed of the motor, an acceleration of the machine tool along the fastening axis, an acceleration of the machine tool across the fastening axis, a rotation of the machine tool centered on the fastening axis, and a yaw rate of the machine tool, that is, a rotation of the machine tool centered on an axis perpendicular to the fastening axis.

[0007] Further aspects and advantages of the machine tool, associated components, and methods of using the same will become apparent from the following description, given by way of example only and with reference to the accompanying drawings.

Brief Description of the Drawings

[0008]

Figure 1

Embodiments for Carrying Out the Invention

[0009] FIG. 1 shows a machine tool 100 for drilling holes and / or fastening screws. In the illustrated embodiment, the machine tool 100 is a hand-held working tool such as an automatic screwdriver. The machine tool 100 includes a housing 105, a motor 110 having a shaft 120 surrounded by the housing 105, a switch 130 formed as a trigger switch, a controller 140 formed as a microcomputer, the controller 140 having a data storage 145 formed as a computer memory, a battery 150, and a communication unit 155 formed as a wireless transmitter. The controller 140 supplies current from the battery 150 to the motor 110 to rotationally drive the shaft 120. The machine tool 100 further includes a gear 160 and a spindle 170 driven by the shaft 120 via the gear 160 and having a screw driving device 175 such as a hexagon drive.

[0010] Furthermore, the machine tool 100 includes a rotational speed sensor 180 for detecting the rotational speed of the motor 110, and an amperage / voltage sensor 190 for detecting the amperage and / or voltage of the current supplied to the motor 110. Further, the machine tool 100 includes several acceleration sensors for detecting the force applied to the shaft, directed towards the machine tool along the fastening axis, the acceleration of the machine tool along the fastening axis, the acceleration of the machine tool across the fastening axis, the rotation of the machine tool about the fastening axis, and the yaw rate of the machine tool, i.e., the rotation of the machine tool about an axis perpendicular to the fastening axis.

[0011] Furthermore, the machine tool 100 includes a line 195 connecting the controller 140 to the motor 110, the switch 130, and the sensors 180, 190 to supply current to the motor 110 and / or collect electrical signals from the switch 130 and / or the sensors 180, 190. Additionally or alternatively, to obtain data regarding the rotational speed, amperage, or voltage of the motor 110, the controller 140 may use information already present from controlling the rotational operation of the motor 110, such as the number of electrical rectifications over time with respect to the rotational speed. The housing 105 includes a grip portion 106 for the user to hold the machine tool 100 by hand such that the switch 130 can be pushed by the user's index finger. The switch 130 can notify the controller 140 of its switch position via the line 195.

[0012] The controller 140 continuously determines a set of parameters characterizing the drilling and / or fastening process, such as the force applied to the shaft, directed towards the machine tool along the fastening axis, the torque about the fastening axis applied to the shaft, the voltage of the current supplied to the motor, the amperage of the current supplied to the motor, the rotational speed of the motor, the acceleration of the machine tool along the fastening axis, the acceleration of the machine tool across the fastening axis, the rotation of the machine tool about the fastening axis, or the yaw rate of the machine tool.

[0013] In use, the power tool 100 can be set up, for example, by selecting the correct clutch settings and gears to operate in a drilling mode. During the drilling process, the controller 140 monitors the motor current and the above-described parameters such as acceleration and yaw rate in all directions as much as possible. The controller 140 recognizes the parameter state of each parameter in a set of parameters as being constant if the change of the parameter over time is below a threshold, or as being changing if the change of the parameter over time exceeds the threshold. For this purpose, for each parameter to be monitored, two signals are derived by using an appropriate filter. The first signal indicates a long-term value (e.g., a current of 10 A as an average over the last 3 seconds of the drilling process). The second signal indicates a shorter-term value (e.g., the average current over the last 30 milliseconds of the drilling process). If the two derived signals exceed a predetermined threshold and are different from each other, the condition counter for the end of drilling is incremented by 1. The controller 140 continuously determines the number of parameters whose parameter state is changing, and if that number is at least 2, 3, 4, or 5 over a predetermined time interval, automatically stops the motor after a waiting time of a fraction of a second. In an alternative embodiment, the waiting time is zero.

[0014] In summary, when the step of the drill bit hits the surface of the base structure, several parameters (e.g., acceleration, motor current) that characterize the drilling process change. The controller 140 recognizes the change and stops the tool. Since the drilling process is reliably stopped at an early point in the process, time is saved, a more accurate shape of the pilot hole is formed, or unnecessary wear is prevented.

[0015] Throughout this application, "the current supplied to the motor" means, when the hand-held power tool is a battery-operated tool, including the current measured within a power supply device such as a battery.

[0016] The foregoing description of the embodiments of the present invention has been presented for purposes of illustration and description. This description is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The described functionality may be distributed among different modules with different numbers and distributions of functionality than those described herein. Additionally, the order in which functions are executed may be varied according to the embodiments. The embodiments were chosen and described as practical applications of the invention to illustrate the principles of the invention and to enable those skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. The technical scope of the present invention is defined by the claims appended hereto and their equivalents.

Claims

1. A method of operating a machine tool for drilling holes in a workpiece and / or fastening a screw along a fastening axis, the machine tool including a motor having a shaft, the method comprising: - supplying an electric current to the motor to rotationally drive the shaft; - continuously determining a set of parameters characterizing the drilling and / or fastening process; - recognizing that the parameter state of each parameter of the set of parameters is constant when the change of the parameter over time is below a threshold; - recognizing that the parameter state of each parameter of the set of parameters is changing when the change of the parameter over time exceeds the threshold; - continuously determining the number of parameters whose parameter states are changing; and - stopping the motor when the number is at least a predefined minimum number over a predefined time interval A method comprising the above.

2. The method according to claim 1, wherein the set of parameters includes at least one of a force applied to the shaft and directed towards the machine tool along the fastening axis, a torque applied to the shaft and centered on the fastening axis, a voltage of the electric current supplied to the motor, an ampere number of the electric current supplied to the motor, a rotational speed of the motor, an acceleration of the machine tool along the fastening axis, an acceleration of the machine tool across the fastening axis, a rotation of the machine tool centered on the fastening axis, and a yaw rate of the machine tool.

3. The method according to claim 1 or 2, wherein the predefined minimum number is 2.

4. The method according to claim 1 or 2, wherein the predefined minimum number is 3.

5. The method according to claim 1 or 2, wherein the predefined minimum number is 4.

6. The method according to claim 1 or 2, wherein the predefined minimum number is 5 or more.

7. The method according to any one of claims 1 to 6, wherein the predefined time interval is zero.

8. A machine tool for drilling holes in a workpiece and / or fastening a screw along a fastening axis, comprising: - a motor having a shaft; - a switch; - A controller configured to supply current to the motor to rotationally drive the shaft, continuously determine a set of parameters characterizing a drilling and / or fastening process, recognize the parameter state of each parameter of the set of parameters as being constant when the change over time of the parameter is below a threshold, recognize the parameter state of each parameter of the set of parameters as being changing when the change over time of the parameter exceeds the threshold, continuously determine the number of parameters whose parameter state is changing, and stop the motor when the number is at least a predefined minimum number over a predefined time interval A machine tool including the same. **Claim 9** The set of parameters includes at least one of a force applied to the shaft and directed toward the machine tool along the fastening axis, a torque applied to the shaft and centered about the fastening axis, a voltage of the current supplied to the motor, an amperage of the current supplied to the motor, a rotational speed of the motor, an acceleration of the machine tool along the fastening axis, an acceleration of the machine tool transverse to the fastening axis, a rotation of the machine tool centered about the fastening axis, and a yaw rate of the machine tool, according to the machine tool of claim 8. **Claim 10** The predefined minimum number is 2, according to the machine tool of claim 8 or 9. **Claim 11** The predefined minimum number is 3, according to the machine tool of claim 8 or 9. **Claim 12** The predefined minimum number is 4, according to the machine tool of claim 8 or 9. **Claim 13** The predefined minimum number is 5 or more, according to the machine tool of claim 8 or 9. **Claim 14** The predefined time interval is zero, according to the machine tool of any one of claims 8 to 13.

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