Intelligent electric screwdriver and control method thereof

Abstract

The application discloses an intelligent electric screwdriver and a control method thereof, which comprises a chuck adapter, a reduction gearbox, a static torque sensor and a motor arranged in a shell in sequence along an axial direction; an output shaft of the motor is connected with an input shaft of the reduction gearbox through a center hole of the static torque sensor; an output shaft of the reduction gearbox is drivingly connected with the chuck adapter; a start-stop switch and a forward-reverse switch are arranged on the shell; the static torque sensor, the motor, the start-stop switch and the forward-reverse switch are electrically connected with a controller and are configured to: when in a forward rotation mode, automatically trigger a multi-stage tightening strategy module comprising three stages of cap recognition, fast screwing and slow tightening; when in a reverse rotation mode, the motor is set to rotate at a preset speed; the scheme can automatically perform a three-stage closed-loop tightening action in the forward rotation mode or a constant-speed loosening action in the reverse rotation mode, without manual judgment of a tightening time or complicated operation, thereby effectively avoiding over-tightening, under-tightening and screw dropping and greatly reducing an operation threshold.

Description

Technical Field

[0001] This invention relates to the field of tightening tool technology, specifically to an intelligent electric screwdriver and its control method. Background Technology

[0002] With the continuous iteration and upgrading of the industrial manufacturing system, intelligent manufacturing has become the core driving force for promoting the high-quality development of the manufacturing industry. Various automated and intelligent production technologies are being applied more and more widely in industrial sites. Tightening operations, as a core and key link in the production process of machinery manufacturing, automobile assembly, aerospace and other fields, directly determine the structural stability, connection reliability and service life of the product by their operation accuracy and quality control level, and have a decisive impact on the overall quality of the final product.

[0003] In the design of electric screwdrivers, accurate torque measurement and closed-loop control are crucial. During screw tightening, real-time and accurate torque sensing can effectively prevent over-tightening or under-tightening, ensuring assembly consistency. Meanwhile, integrated sensing and fast-response control strategies can automatically switch according to tightening and loosening conditions, significantly improving assembly efficiency and reliability.

[0004] However, existing electric screwdriver designs are significantly limited in torque sensing and integrated control. Dynamic sensor solutions rely on brushes or slip rings to transmit signals, which suffer from severe wear and tear over long-term use, leading to decreased reliability and high costs. Static sensor solutions, while eliminating brushes, introduce multiple components such as independent drive shafts and flanges, resulting in cumbersome assembly, low coaxiality and transmission rigidity, and excessively long axial dimensions, making it difficult to meet the trend of miniaturization and dexterity in handheld tools. Furthermore, the start / stop and forward / reverse switches are independent of each other, requiring manual control by the operator based on experience, and cannot form an automatic switching closed-loop strategy.

[0005] For example, one existing electric screwdriver incorporates a force detection component along the power transmission path of the transmission structure, indirectly measuring torque by detecting deformation of the transmission components. While this approach achieves closed-loop control, the force detection component must contact the transmission components and relies on multiple stages of transmission components, including a reduction gear, a first transmission component, and a second transmission component. This results in a complex structure, a long axial dimension, and the detection element directly bearing the transmission load, leading to wear and signal drift over long-term use. Another electric screwdriver optimizes the housing layout and switch position, separating the motor from the handheld part, but it lacks any torque sensor, still relying on current detection and manual switch control, thus failing to achieve precise torque closed-loop control. Furthermore, none of the aforementioned existing solutions address the issue of intelligent linkage between forward / reverse rotation and start / stop functions. The tightening process lacks segmented, precise control, parameter configuration is inconvenient, and result feedback is not intuitive.

[0006] Therefore, existing electric screwdrivers have significant shortcomings in terms of sensor integration, miniaturization, and intelligent control, making it difficult to achieve high-precision, fast-response tightening operations. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, this invention provides an intelligent electric screwdriver and its control method, which aims to highly integrate a torque sensor and a transmission system within a limited space to achieve precise real-time torque feedback and adaptive control, thereby significantly improving the tightening accuracy and operational dexterity of the electric screwdriver.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, a smart electric screwdriver is provided, comprising a bit adapter, a reduction gearbox, a static torque sensor, and a motor arranged sequentially along the axial direction within a housing; the output shaft of the motor passes through the central hole of the static torque sensor and is connected to the input shaft of the reduction gearbox, and the output shaft of the reduction gearbox is drively connected to the bit adapter; a start / stop switch and a forward / reverse switch are provided on the housing, and the static torque sensor, motor, start / stop switch, and forward / reverse switch are all electrically connected to a controller and configured as follows: When in forward rotation mode, the multi-stage tightening strategy module, which includes three stages: cap recognition, rapid screwing in, and slow tightening, is automatically triggered; when in reverse rotation mode, the motor reverses at a preset speed.

[0009] Furthermore, the static torque sensor is pressed and fixed inside the housing by a sleeve, and the static torque sensor and the motor are radially positioned and connected by the cooperation of the positioning pin and the positioning hole. The static torque sensor and the gearbox are snapped together by the cooperation of the positioning groove and the protrusion, and are locked to the static torque sensor by the screws distributed around the gearbox.

[0010] Furthermore, the start / stop switch is a non-contact magnetic switch.

[0011] Furthermore, the rear end of the housing is provided with an aviation interface for electrical connection with the controller.

[0012] Secondly, a control method for an intelligent electric screwdriver is provided, which includes the following steps: S1: Detect the status of the forward / reverse switch. If the current mode is reverse, proceed to step S2; if the current mode is forward, proceed to step S3. S2: In response to the triggering of the start / stop switch, the drive motor reverses to perform open-loop loosening, and controls the motor to stop reversing when the start / stop switch is released; S3: In response to the triggering of the start / stop switch, execute a multi-stage tightening strategy including a cap recognition stage, a rapid screw-in stage, and a slow tightening stage; S4: Turn off the start / stop switch and return to step S1 to wait for the next operation.

[0013] Furthermore, step S3 specifically includes: S31: The controller acquires the torque signal from the static torque sensor in real time and simultaneously activates the torque loop, speed loop, and current loop. S32: The torque ring monitors the actual torque value in real time and compares it with the preset capping torque upper limit, rapid start torque threshold and target torque qualified range; S33: Based on the comparison results of the torque ring, the automatic control switches sequentially from the cap recognition stage to the rapid screw-in stage and then to the slow tightening stage, and controls the motor to stop when the target torque qualified range is reached; S34: The speed loop monitors the motor speed in real time and outputs the current setpoint according to the preset target speed for each stage. The current loop controls the motor speed according to the current setpoint to form a cascade control. Furthermore, the controller responds to the mode switching command of the forward / reverse switch when the motor is stationary, and blocks the mode switching command when the motor is running.

[0014] Furthermore, the control method also includes a parameter configuration method before executing step S1: the host computer sends the tightening parameters to the controller via the CAN bus. The tightening parameters include at least: the target speed and the upper limit of the cap recognition torque during the cap recognition stage, the target speed and the threshold of the rapid screw-in torque during the rapid screw-in stage, and the target speed and the qualified range of the target torque during the slow tightening stage.

[0015] The beneficial effects of this invention are as follows: 1. This solution adopts a layout where the motor output shaft directly passes through the hollow static torque sensor and connects to the gearbox, completely eliminating intermediate components such as independent drive shafts and flanges, reducing the axial dimension by more than 20%. At the same time, the motor, sensor, and gearbox are locked into a rigid whole by circumferential and axial screws. The asymmetrical fixing method, which uses screws on one end and pre-positioned slots and screws on the other end, greatly improves the connection rigidity and coaxiality, making the whole machine compact, reliable, and perfectly suited to the miniaturization requirements of handheld tools.

[0016] 2. This solution eliminates the brushes or slip rings used in existing dynamic sensor solutions and adopts a static torque sensor fixed to the housing, completely eliminating rotational contact wear, resulting in high signal stability and long service life. At the same time, it achieves the separation of torque measurement and power transmission in physical structure. The static torque sensor does not bear the main transmission load, and the signal is not affected by transmission fluctuations and assembly gaps, thus fundamentally improving measurement accuracy and anti-interference ability.

[0017] 3. This solution achieves mode-dependent one-button intelligent operation through the linkage design of forward / reverse switch and magnetic start / stop switch, combined with control strategy. Users only need to select forward or reverse mode and press the switch, and the electric screwdriver can automatically perform a three-stage closed-loop tightening action in forward rotation or an open-loop loosening action in reverse rotation. There is no need for manual judgment of tightening time or complex operation, which effectively avoids over-tightening, under-tightening and screw falling, and greatly reduces the operation threshold.

[0018] 4. This solution adopts a design where the torque loop is activated throughout the entire process and outputs stage switching commands independently, which differs from existing technologies where the torque loop is activated only during the low-speed constant speed stage or where the torque loop directly controls the drive current. Throughout the entire process of cap recognition, rapid screwing in, and slow tightening, the torque loop continuously monitors the torque in real time and compares it with a preset threshold, only outputting stage switching or stop signals. Meanwhile, the speed loop and current loop form a cascade control, independently responsible for motor speed regulation. This architecture fundamentally avoids abrupt state changes and torque shocks during control mode switching, achieving smooth and precise stage transitions. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The above and other objects, features, and advantages of the present invention will become clearer through the accompanying drawings. The same reference numerals indicate the same parts in all the drawings. The drawings are not intentionally drawn to scale to actual dimensions; the focus is on illustrating the main points of the invention.

[0020] Figure 1 This is a schematic diagram of the structure of an intelligent electric screwdriver.

[0021] Figure 2 This is an exploded view of a smart electric screwdriver.

[0022] Figure 3 This is a schematic diagram of the structure of the motor, static torque sensor and gearbox.

[0023] Figure 4 This is an exploded view of the motor and the static torque sensor working together.

[0024] Figure 5 This is an exploded view of the static torque sensor and its connection to the gearbox.

[0025] Figure 6 A diagram illustrating the three-stage tightening strategy.

[0026] Among them, 10. Bit adapter, 11. Motor housing, 12. Handle housing, 13. Control circuit board housing, 14. Aviation interface, 15. Hex countersunk screw, 20. Forward / reverse switch, 21. Start / stop switch, 30. Gearbox, 31. Static torque sensor, 32. Motor, 33. Phillips countersunk screw, 34. Socket head screw, 35. Fixing cover, 40. Electric screwdriver drive and control integrated circuit board, 41. Magnetic encoder circuit board, 50. Socket. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0029] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0030] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0031] like Figures 1 to 5 As shown, the intelligent electric screwdriver of this solution includes a bit adapter 10, a reduction gearbox 30, a static torque sensor 31, and a motor 32 arranged sequentially along the axial direction within the housing. The output shaft of the motor 32 passes through the center hole of the static torque sensor 31 and is connected to the input shaft of the reduction gearbox 30. The output shaft of the reduction gearbox 30 is connected to the bit adapter 10 via a transmission connection. A start / stop switch 21 and a forward / reverse switch 20 are provided on the housing. The static torque sensor 31, the motor 32, the start / stop switch 21, and the forward / reverse switch 20 are all electrically connected to the controller and configured as follows: When in forward rotation mode, the multi-stage tightening strategy module, which includes three stages: cap recognition, rapid screwing in, and slow tightening, is automatically triggered; when in reverse rotation mode, the motor 32 reverses at a preset speed.

[0032] The housing includes a motor housing 11, a grip housing 12, and a control circuit board housing 13. The controller includes an electric screwdriver integrated control circuit board 40 and a magnetic encoder circuit board 41 housed in the grip housing 12, and a control circuit board housed in the control circuit board housing 13. The magnetic encoder circuit board 41 is mounted and fixed by a fixing cover 35. The tail end of the control circuit board housing 13 is provided with an aviation interface 14 that is electrically connected to the control circuit board. The aviation interface 14 is fixed by a countersunk hex screw 15 and is used to connect an external power supply and communication cable. The start / stop switch 21 is a non-contact magnetic switch. The start / stop switch 21 and the forward / reverse switch 20 are located on the surface of the grip housing 12. The start / stop switch 21 and the forward / reverse switch 20 are linked to generate a start / stop trigger signal.

[0033] The static torque sensor 31 is pressed and fixed inside the housing by the sleeve 50, and the static torque sensor 31 and the motor 32 are radially positioned and connected by the cooperation of the positioning pin and the positioning hole. The positioning pin is preferably an internal hex screw 34. The static torque sensor 31 and the gearbox 30 are snapped together by the cooperation of the positioning groove and the protrusion, and are locked to the static torque sensor 31 by the circumferentially distributed cross countersunk screws 33 of the gearbox 30, so as to ensure that the static torque sensor 31 does not rotate with the motor 32 shaft and has no axial movement.

[0034] This solution also provides a control method for intelligent electric screwdrivers, which includes the following steps: S1: Detect the status of the forward / reverse switch 20. If it is currently in reverse mode, proceed to step S2. If it is currently in forward mode, proceed to step S3. S2: In response to the triggering of the start / stop switch 21, the drive motor 32 reverses to perform open-loop loosening, and controls the motor 32 to stop reversing when the start / stop switch 21 is released; S3: In response to the triggering of the start / stop switch 21, execute a multi-stage tightening strategy including a cap recognition stage, a rapid screw-in stage, and a slow tightening stage; specifically including: S31: The control circuit board acquires the torque signal from the static torque sensor 31 in real time and simultaneously activates the torque loop, speed loop, and current loop. S32: The torque ring monitors the actual torque value in real time and compares it with the preset capping torque upper limit, rapid start torque threshold and target torque qualified range; S33: Based on the comparison results of the torque ring, the automatic control switches from the cap recognition stage to the rapid screw-in stage and then to the slow tightening stage in sequence, and controls the motor 32 to stop when the target torque qualified range is reached; S34: The speed loop monitors the speed of motor 32 in real time and outputs the current setpoint according to the preset target speed of each stage. The current loop controls the speed of motor 32 according to the current setpoint to form a cascade control. S4: Release the start / stop switch 21 and return to step S1 to wait for the next operation.

[0035] The control method of the intelligent electric screwdriver in this solution also includes a parameter configuration method before executing step S1: the host computer sends the tightening parameters to the control circuit board via the CAN bus. The tightening parameters include at least: the target speed and the upper limit of the cap recognition torque during the cap recognition stage, the target speed and the threshold of the rapid screwing in stage, and the target speed and the qualified range of the target torque during the slow tightening stage. The control circuit board responds to the mode switching command of the forward and reverse switch 20 when the motor 32 is stationary, and blocks the mode switching command when the motor 32 is running.

[0036] In its implementation, this solution employs a three-stage tightening strategy in forward rotation mode, combining full-range torque monitoring with speed-current cascade control, as detailed below: The electric screwdriver simultaneously activates the torque loop, speed loop, and current loop, nested from the outside in. The current loop collects the three-phase current of the motor 32 stator in real time, compares it with the current setpoint output by the speed loop, and outputs the drive voltage after PI regulation, realizing closed-loop control of the motor 32 current with a response period in the microsecond range. The speed loop collects the actual speed of the motor 32 in real time, compares it with the target speed preset by the host computer for each stage, and outputs the current setpoint to the current loop after PI regulation with a control period in the millisecond range. The speed loop and current loop form a cascade control structure. The torque loop collects the actual torque fed back by the torque sensor installed on the output shaft of the electric screwdriver in real time, compares it with the preset torque threshold for each stage, and outputs stage switching signals and stop signals based on the comparison results. The torque loop does not participate in the setpoint regulation of the speed loop or current loop, so it will not cause sudden changes in the control state. The torque loop remains active in the cap recognition stage, the rapid screw-in stage, and the slow tightening stage, and does not depend on any triggering conditions or the low-speed constant speed stage.

[0037] Compared with the ordinary segmented trigger-type torque loop control scheme, which first operates at high speed, then at low speed and constant speed, and only activates the torque loop when the torque exceeds a threshold, this scheme has the following essential differences: Full-process activation: The torque loop participates in control from the start of tightening, without waiting for the low-speed constant speed stage, solving the blind spot of no torque intervention in the existing solution during the cap recognition and rapid screw-in stages; Output switching signal: The torque loop outputs a stage switching command instead of directly driving the current. The speed loop and current loop form a cascade independent operation, avoiding the sudden change in control state and torque shock when switching from the speed loop to the torque loop in the existing solution; Threshold segmentation: Independent torque thresholds are set for cap recognition, rapid screw-in, and slow tightening to achieve fine-grained stage control.

[0038] Throughout the tightening process, the torque loop continuously monitors the actual torque and automatically controls the switching between stages of cap recognition, rapid screwing in, and slow tightening, as well as the final shutdown, based on the threshold comparison results. The speed loop operates independently according to the target speed preset by the host computer for each stage, and the current loop realizes closed-loop regulation of the motor current. The three work together without the need to switch control modes between the speed stage and the torque stage.

[0039] The following example, taking the tightening of an M3×8 Phillips head pan head screw (target torque 0.80 N·m), illustrates the implementation steps of the control method in detail.

[0040] Step 1: Parameter setting. The operator inputs parameters via the HMI touchscreen on the host computer, such as... Figure 6 The tightening parameters shown are packaged into a CAN message by the host computer and sent to the control circuit board inside the electric screwdriver via the CAN bus; the control circuit board receives the message and stores it in non-volatile memory.

[0041] Step 2: Start tightening. The user presses the start / stop switch 21 on the electric screwdriver. The control circuit board simultaneously activates the torque loop, speed loop, and current loop. The current loop runs with a period of 50μs, while the speed loop and torque loop both run with a period of 1ms. From this point on, the torque loop continuously monitors the actual torque on the output shaft.

[0042] Step 3: During the cap recognition stage, the speed loop operates at the target speed of 50 rad / s, the motor rotates at low speed 32, and the bit searches for the screw head and engages correctly; the torque loop monitors the actual torque in real time. When the bit contacts the screw and begins to generate load, the actual torque increases. Once the actual torque reaches the upper limit of the cap recognition torque of 0.02 N·m, the torque loop outputs a cap recognition completion signal, and the system automatically switches to the rapid screw-in stage.

[0043] Step 4: In the rapid screwing stage, the target speed of the speed loop is switched to 200 rad / s, and the motor 32 accelerates to this speed, so that the screw is quickly screwed into the workpiece; the torque loop continues to monitor the actual torque; when the actual torque reaches the rapid starting torque threshold of 0.10 N·m, the torque loop outputs a rapid completion signal, and the system switches to the slow tightening stage.

[0044] Step 5: During the slow tightening stage, the speed loop switches to the slow target speed of 20 rad / s, and the motor 32 runs at low speed to precisely tighten the screw; the torque loop continuously collects the actual torque and compares it with the target torque of 0.80 N·m. When the actual torque enters the preset qualified range of 0.80~0.84 N·m, the torque loop issues a stop command, and the motor 32 immediately stops running.

[0045] Step 6: Result Judgment and Feedback. After motor 32 stops, the control circuit board reads the final steady-state torque value, for example, the measured value is 0.82 N·m, and compares it with the acceptable range of 0.80~0.84 N·m. Since 0.82 N·m falls within the range, the control circuit board outputs an OK signal: the green indicator light at the tail of the electric screwdriver lights up, and at the same time, it sends "OK" and the actual torque value to the host computer via the CAN bus. The host computer's data display page can display "OK" and the final steady-state torque value of 0.82 N·m in real time. If the actual torque is 0.86 N·m, it exceeds the upper limit of the acceptable range, and an NG signal is output: the red indicator light lights up, the host computer displays NG and the final steady-state torque value, and records the unacceptable data.

[0046] This solution supports remote configuration of all tightening parameters via CAN bus, eliminating the need to disassemble the machine during production line changes and enabling parameter distribution within seconds. After tightening, the system automatically compares the results with preset ranges, outputs OK / NG judgments in real time via indicator lights and the bus, and uploads data such as actual torque and time consumption at each stage to the host computer, providing complete data support for process optimization and quality traceability.

[0047] Although the specific embodiments of the invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent; various modifications and variations that can be made by a person skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A smart electric screwdriver, characterized in that, The device includes a bit adapter, a gearbox, a static torque sensor, and a motor arranged sequentially along the axial direction within the housing; the output shaft of the motor passes through the center hole of the static torque sensor and is connected to the input shaft of the gearbox; the output shaft of the gearbox is connected to the bit adapter in a driving connection. The housing is equipped with a start / stop switch and a forward / reverse switch. The static torque sensor, motor, start / stop switch, and forward / reverse switch are all electrically connected to the controller and configured as follows: When in forward rotation mode, the multi-stage tightening strategy module, which includes three stages: cap recognition, rapid screwing in, and slow tightening, is automatically triggered; when in reverse rotation mode, the motor reverses at a preset speed.

2. The intelligent electric screwdriver according to claim 1, characterized in that, The static torque sensor is pressed and fixed inside the housing by a sleeve, and the static torque sensor and the motor are radially positioned and connected by the cooperation of the positioning pin and the positioning hole. The static torque sensor and the gearbox are snapped together by the cooperation of the positioning groove and the protrusion, and are locked to the static torque sensor by the screws distributed around the gearbox.

3. The intelligent electric screwdriver according to claim 1, characterized in that, The start / stop switch is a non-contact magnetic switch.

4. The intelligent electric screwdriver according to claim 1, characterized in that, The rear end of the housing is provided with an aviation interface that is electrically connected to the controller.

5. A control method for an intelligent electric screwdriver, applied to the intelligent electric screwdriver according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Detect the status of the forward / reverse switch. If the current mode is reverse, proceed to step S2; if the current mode is forward, proceed to step S3. S2: In response to the triggering of the start / stop switch, the drive motor reverses to perform open-loop loosening, and controls the motor to stop reversing when the start / stop switch is released; S3: In response to the triggering of the start / stop switch, execute a multi-stage tightening strategy including a cap recognition stage, a rapid screw-in stage, and a slow tightening stage; S4: Turn off the start / stop switch and return to step S1 to wait for the next operation.

6. The control method for the intelligent electric screwdriver according to claim 5, characterized in that, Step S3 specifically includes: S31: The controller acquires the torque signal from the static torque sensor in real time and simultaneously activates the torque loop, speed loop, and current loop. S32: The torque ring monitors the actual torque value in real time and compares it with the preset capping torque upper limit, rapid start torque threshold and target torque qualified range; S33: Based on the comparison results of the torque ring, the automatic control switches sequentially from the cap recognition stage to the rapid screw-in stage and then to the slow tightening stage, and controls the motor to stop when the target torque qualified range is reached; S34: The speed loop monitors the motor speed in real time and outputs the current setpoint according to the preset target speed for each stage. The current loop controls the motor speed according to the current setpoint to form a cascade control.

7. The control method for the intelligent electric screwdriver according to claim 5, characterized in that, The controller responds to the mode switching command of the forward / reverse switch when the motor is stationary, and disables the mode switching command when the motor is running.

8. The control method for the intelligent electric screwdriver according to claim 5, characterized in that, It also includes a parameter configuration method before executing step S1: the host computer sends the tightening parameters to the controller via the CAN bus. The tightening parameters include at least: the target speed and the upper limit of the cap recognition torque during the cap recognition stage, the target speed and the threshold of the rapid screw-in torque during the rapid screw-in stage, and the target speed and the qualified range of the target torque during the slow tightening stage.

Images