Machine tool and method for operating a machine tool

Abstract

A machine tool and method for fastening a screw, the machine tool comprising: a motor having a shaft; a controller configured to supply an electric current to the motor to rotationally drive the shaft, continuously determine a first parameter characterizing the fastening process, recognize a screw engagement start point when the first parameter satisfies a predefined set of conditions, determine a second parameter that affects a time difference between the recognized screw engagement start point and an actual screw engagement start point, calculate a target rotational speed to be performed by the motor after the recognized screw engagement start point depending on the second parameter, and stop the motor when the motor has performed a rotation of the target number after the recognized screw engagement start point.

Description

Technical Field

[0001] A machine tool for fastening a screw and a method of operating the machine tool are described herein. A hand-held power tool for enabling such screw fastening is also described. Generally, such hand-held tools are widely used in the construction industry. Typical hand-held tools within the technical scope of the present invention include, but are not limited to, an automatic screwdriver for screwing a screw into a workpiece, thereby fastening the workpiece such as a metal plate with the screw.

Background Art

[0002] A hand-held power tool for enabling screw fastening is 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. The tool may also include a controller for controlling the motor and continuously determining some parameters of the drilling or fastening process, such as the transmitted torque and rotational speed of the rotating shaft, during use of the tool.

[0003] One possible application field is the fastening of self-tapping and self-sealing screws into pre-drilled holes. The sealing performance may depend on the fastening depth of the fastening element in the pre-drilled hole. Such an operation is usually performed using a depth gauge that needs to be calibrated under specific circumstances, which can be cumbersome and / or time-consuming.

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 attaching a screw to a workpiece 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 first parameter characterizing the fastening process, recognizing a screw engagement start point when the first parameter satisfies a predefined set of conditions, determining a second parameter that affects the time difference between the recognized screw engagement start point and the actual screw engagement start point, calculating a target rotational speed to be performed by the motor after the recognized screw engagement start point based on the second parameter, and stopping the motor when the motor has performed the target number of rotations after the recognized screw engagement start point.

[0005] According to another aspect, a machine tool for drilling a hole in a workpiece and / or attaching 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 first parameter characterizing the fastening process, recognize a screw engagement start point when the first parameter satisfies a predefined set of conditions, and determine or continuously determine a second parameter that affects the time difference between the recognized screw engagement start point and the actual screw engagement start point, calculate a target rotational speed to be performed by the motor after the recognized screw engagement start point based on the second parameter, and stop the motor when the motor has performed the target number of rotations after the recognized screw engagement start point.

[0006] According to another aspect, the first parameter includes at least one of the voltage of the electric current supplied to the motor, the amperage of the electric current supplied to the motor, the power consumption of the electric current supplied to the motor, the rotational speed of the motor, changes over time thereof, and combinations thereof.

[0007] In a preferred embodiment, the determination of the second parameter is made before the recognized start point of the screw engagement. In an alternative or additional embodiment, the determination of the second parameter is made after the recognized start point of the screw engagement.

[0008] According to another embodiment, the second parameter includes at least one of the force applied to the shaft and directed towards the machine tool along the fastening axis, the torque applied to the shaft and centered on the fastening axis, the voltage of the current supplied to the motor, the amperage of the current supplied to the motor, the power consumption 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 centered on the fastening axis, the yaw rate of the machine tool, the temperature of the machine tool, the change over time of these, and the combination of these.

[0009] Further embodiments and advantages of the machine tool, related 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

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] FIG. 1 shows a machine tool 100 for making holes and / or fastening screws. In the illustrated embodiment, the machine tool 100 is a handheld working tool such as an electric 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 screw drive 175 such as a hex drive, and a spindle 170 driven by the shaft 120 via the gear 160.

[0012] 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 toward 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.

[0013] Furthermore, the machine tool 100 includes a line 195 that connects 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.

[0014] In use, the machine tool 100 can be set up, for example, by selecting appropriate clutch settings and gears to activate a particular screw tightening mode. During this tightening process, the controller 140 monitors several parameters such as the voltage, amperage, and power consumption of the current supplied to the motor, the rotational speed of the motor, the force applied to the shaft and directed towards the machine tool along the tightening axis, the torque applied to the shaft about the tightening axis, the acceleration of the machine tool along the tightening axis, the acceleration of the machine tool across the tightening axis, the rotation of the machine tool about the tightening axis, the yaw rate of the machine tool, and the temperature of the machine tool. Further, the controller 140 monitors the change over time of these parameters.

[0015] When, for example, a first parameter such as the power consumption of the current supplied to the motor satisfies a predefined set of conditions such as a minimum value of the time after the start-up phase of the machine tool followed by an increase, the controller 140 recognizes the start point of screw engagement. Next, in order to complete the screwing process at an appropriate location, the controller 140 calculates the target rotational speed to be performed by the motor after the recognized start point of screw engagement, and stops the motor when the motor has rotated the target number of rotations after the recognized start point of screw engagement. However, the recognized start point of screw engagement may not exactly match the actual start point of screw engagement. In order to compensate for the time difference between the recognized start point of screw engagement and the actual start point of screw engagement, when calculating the target rotational speed, the controller 140 takes into account one or more second parameters that can affect the above time difference. For this purpose, a non-linear model formula derived using well-known statistical methods during the development or testing of the machine tool may be used. The controller 140 may determine the second parameter before and / or after the recognized start point of screw engagement.

[0016] In summary, when the thread of the screw starts tapping the hole in the base structure, the controller 140 recognizes the specific behavior of some parameters that affect the time difference between the recognized start point of screw engagement and the actual start point of screw engagement. The controller then stops the motor after the target number of rotations. The screwing process is reliably stopped at an appropriate location, thus resulting in, for example, more accurate compression of the seal element.

[0017] Throughout this application, "the current supplied to the motor" means including the current measured within a power supply device such as a battery when the hand-held power tool is a battery-operated tool.

[0018] 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 form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The functionality described may be distributed among different modules with different numbers and distributions of functionality from that 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 one of ordinary skill 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

Claim 1 A method of operating a machine tool for attaching a screw to a workpiece 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 first parameter characterizing the fastening process; - Recognizing the screw engagement start point when the first parameter satisfies a predefined set of conditions; - Determining a second parameter affecting the time difference between the recognized screw engagement start point and the actual screw engagement start point; - Calculating a target rotational speed to be performed by the motor after the recognized screw engagement start point based on the second parameter; and - Stopping the motor when the motor has rotated the target number of rotations after the recognized screw engagement start point A method comprising. Claim 2 The method according to claim 1, wherein the first parameter includes at least one of the voltage of the electric current supplied to the motor, the amperage of the electric current supplied to the motor, the power consumption of the electric current supplied to the motor, the rotational speed of the motor, the change over time thereof, and combinations thereof. Claim 3 The method according to claim 1 or 2, wherein determining the second parameter includes continuously determining the second parameter. Claim 4 The method according to any one of claims 1 to 3, wherein determining the second parameter is performed before the recognized screw engagement start point. Claim 5 The method according to any one of claims 1 to 4, wherein determining the second parameter is performed after the recognized screw engagement start point. Claim 6 The method according to any one of claims 1 to 5, wherein the second parameter includes at least one of a force applied to the shaft and directed toward the machine tool along the fastening shaft, a torque applied to the shaft and centered on the fastening shaft, a voltage of the current supplied to the motor, an ampere number of the current supplied to the motor, a power consumption of the current supplied to the motor, a rotational speed of the motor, an acceleration of the machine tool along the fastening shaft, an acceleration of the machine tool across the fastening shaft, a rotation of the machine tool centered on the fastening shaft, a yaw rate of the machine tool, a temperature of the machine tool, a change over time thereof, and a combination thereof.

7. A machine tool for drilling a hole in a workpiece and / or fastening a screw along a fastening shaft, - a motor having a shaft, - a switch, - a controller configured to supply an electric current to the motor to rotationally drive the shaft, continuously determine a first parameter characterizing a fastening process, recognize a screw engagement start point when the first parameter satisfies a predefined set of conditions, determine a second parameter that affects a time difference between the recognized screw engagement start point and an actual screw engagement start point, calculate a target rotational speed to be performed by the motor after the recognized screw engagement start point based on the second parameter, and stop the motor when the motor has rotated at the target number of rotations after the recognized screw engagement start point is included in the machine tool.

8. The machine tool according to claim 7, wherein the first parameter includes at least one of a voltage of the current supplied to the motor, an ampere number of the current supplied to the motor, a power consumption of the current supplied to the motor, a rotational speed of the motor, a change over time thereof, and a combination thereof.

9. The machine tool according to claim 7 or 8, wherein the controller is configured to continuously determine the second parameter.

10. The machine tool according to any one of claims 7 to 9, wherein the controller is configured to determine the second parameter before the recognized screw engagement start point.

11. The controller is configured to determine the second parameter after the recognized start time of the screw engagement, the machine tool according to any one of claims 7 to 10.

12. The second parameter 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 on the fastening axis, a voltage of the current supplied to the motor, an ampere number of the current supplied to the motor, a power consumption 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, a yaw rate of the machine tool, a temperature of the machine tool, a change over time of these, and a combination of these, the machine tool according to any one of claims 7 to 11.

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