An electric hammer adaptive load speed control system

Abstract

This invention discloses an adaptive load speed control system for electric hammers, relating to the field of power tool control technology. It includes a projection warning end, an angle detection end, and a graded color difference end. The load sensing end is used to collect the current waveform and axial vibration spectrum of the hammer shell in real time, extracting the effective current value, current change rate, and axial vibration amplitude, and sending a fast response mode trigger signal. The load status judgment end determines the current load level by comparing the effective current value with a preset threshold range, identifies the material type based on a three-dimensional feature vector, predicts the load change trend, and outputs a comprehensive set of control parameters. The speed and torque control end performs closed-loop adjustment based on the control parameter set, causing the PWM modulation module to generate a drive signal, and implementing overcurrent protection, mode switching, and torque limiting through an inertial start protection module. This invention can identify load type and material changes in real time, achieving smooth speed regulation without impact, improving the working efficiency and safety of the electric hammer.

Description

Technical Field

[0001] This invention relates to the field of power tool control technology, and in particular to an adaptive load speed control system for electric hammers. Background Technology

[0002] An electric hammer drill is a power tool that combines rotary cutting and impact crushing to drill holes in hard and brittle materials such as concrete, stone, and brick walls. In actual operation, the load on the electric hammer drill exhibits typical nonlinear and highly time-varying characteristics. When the drill bit contacts the workpiece from an unloaded state, during the transition between material layers of different hardness, or when encountering local anomalies such as reinforcing bars or voids during drilling, the load torque can change dramatically in a very short time.

[0003] Currently, due to the frequent and drastic load changes during drilling with electric hammers, most existing speed control systems employ constant speed or simple segmented control based on a single current threshold. These systems cannot detect in real time the differences in load characteristics when the drill bit encounters different materials such as concrete, steel, and wood, leading to a mismatch between speed and torque output and operating conditions, resulting in low drilling efficiency and a high risk of stuck drills. Furthermore, existing systems struggle to identify transient load changes. When the electric hammer suddenly transitions from light-load idling to heavy-load impact, the lack of a rapid response mechanism causes lag in PID parameter switching and significant torque impact, affecting operational stability. For the common but difficult-to-accurate fault condition of slippage in the hammer's toothed section, existing technologies lack effective vibration spectrum diagnostic methods, making it impossible to provide early warnings or adaptively adjust control strategies.

[0004] Therefore, an adaptive load speed control system for electric hammers is proposed to solve the above problems. Summary of the Invention

[0005] The main objective of this invention is to provide an adaptive load speed control system for electric hammers to solve the problems mentioned in the background.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: an adaptive load speed control system for electric hammers, the system comprising a load sensing end, a load state judgment end, and a speed and torque control end;

[0007] The load sensing end is used to collect the current waveform and the axial vibration spectrum of the shell during the operation of the electric hammer in real time, extract the effective value of the current, the rate of change of the current and the amplitude of the axial vibration, and send the fast response mode trigger signal to the load status judgment end.

[0008] The load status judgment terminal is used to determine the current load level by comparing the received current effective value with a preset threshold range and output the load level code. It identifies the material type based on the three-dimensional feature vector composed of the current effective value, current change rate and axial vibration amplitude. At the same time, it predicts the load change trend by calculating the slope and integral value of the current sampling value and outputs a set of control parameters containing the target speed command.

[0009] The speed and torque control terminal performs closed-loop regulation through the PID adjustment module based on the control parameter set, so that the PWM modulation module generates a drive signal, and the inertial start protection module realizes overcurrent protection, mode switching and torque limiting, so as to adaptively control the speed and output torque of the electric hammer motor.

[0010] Preferably, the load sensing terminal includes a current sampling module, a vibration detection module, and a speed feedback module;

[0011] The current sampling module includes a current effective value unit and a current change rate unit;

[0012] The current RMS value unit uses the sliding window root mean square algorithm to calculate the current RMS value within one power frequency cycle to characterize the steady-state load size;

[0013] The current change rate unit calculates the ratio of the current increment to the time interval between adjacent sampling points using a differential algorithm. When the ratio exceeds a preset sudden change threshold, a load transient impact flag is output, and the transient impact flag is used to trigger the load status judgment terminal to enter the fast response mode. In the fast response mode, the comparison period of the interval decision unit of the load status judgment terminal is shortened to 1 / 4 of the normal period, and the time threshold of the integral decision unit of the trend prediction module is reduced to 1 / 3 of the normal value.

[0014] Preferably, the vibration detection module includes an axial vibration unit and a rotational speed and frequency extraction unit;

[0015] The axial vibration unit collects the axial impact vibration amplitude of the hammer shaft head through a piezoelectric accelerometer, and extracts the DC component of the impact energy after filtering.

[0016] The rotational speed and frequency extraction unit converts the time-domain vibration signal into a frequency-domain spectrum through a fast Fourier transform, extracts the harmonic amplitude corresponding to the electric hammer impact frequency and its harmonics, compares the harmonic amplitude with the reference amplitude under normal operating conditions, and if the second harmonic amplitude exceeds 60% of the fundamental amplitude and the current change rate repeatedly exceeds the sudden change threshold, it is determined to be a slipping state of the toothed tooth, and the state code is sent to the load state judgment terminal.

[0017] Preferably, the speed feedback module includes a Hall pulse counting unit and a speed conversion unit;

[0018] The Hall pulse counting unit detects the pulse signal output by the motor in real time when the motor rotates through the Hall sensor at the tail end of the motor, and uses a timer to measure the time interval between adjacent pulses.

[0019] The speed conversion unit calculates the current actual speed value based on the number of pulses corresponding to each revolution of the motor using the frequency-speed conversion formula. This value is used as feedback to participate in closed-loop control, and the actual speed value is simultaneously fed back to the load status judgment terminal and the speed-torque control terminal.

[0020] Preferably, the load status determination terminal includes a load comparison module, a material identification module, and a trend prediction module;

[0021] The load comparison module includes a threshold storage unit and an interval decision unit;

[0022] The threshold storage unit pre-stores the current threshold ranges of the electric hammer under different working voltages (light load, medium load, heavy load, and stall) through a non-volatile memory.

[0023] The interval decision unit compares the current measured effective value of the current with the threshold interval step by step through a numerical comparator. If the current exceeds the stall threshold, a stall flag signal is output; otherwise, a digital code corresponding to the load level is output. When a fast response mode trigger signal is received from the load sensing end, the comparison cycle is shortened to 1 / 4 of the normal cycle.

[0024] Preferably, the material identification module includes a current and vibration combined feature unit and a lookup table discrimination unit;

[0025] The current and vibration combined feature unit synchronously collects the effective value of current, the rate of change of current and the amplitude of axial vibration, and normalizes the three to form a three-dimensional feature vector.

[0026] The lookup and discrimination unit performs nearest neighbor matching between the three-dimensional feature vector and the pre-stored standard feature vectors of different materials, outputs the material type of the current structure, and outputs an unknown material flag when the nearest neighbor distance between the three-dimensional feature vector and the pre-stored standard feature vector exceeds a set threshold. It also automatically sets the control parameter set to the medium load balance parameter and temporarily increases the current change rate threshold by 20% to reduce the risk of misjudgment.

[0027] Preferably, the trend prediction module includes a slope calculation unit and an integral decision unit;

[0028] The slope calculation unit calculates the slope value of the most recent N current sampling values ​​over time using the least squares method. If the slope is positive and greater than the rising threshold, it is determined that the load is overloaded. If the slope is negative and the absolute value is greater than the falling threshold, it is determined that the load is becoming lighter.

[0029] The integral decision unit accumulates and integrates multiple consecutive slope values. When the integral value exceeds a predetermined time threshold, it outputs a load state stabilization signal to suppress misjudgments caused by instantaneous disturbances. In fast response mode, the time threshold is reduced to 1 / 3 of the normal value.

[0030] Preferably, the speed torque control terminal includes a PWM modulation module, a PID adjustment module, and an inertial start protection module;

[0031] The PWM modulation module includes a duty cycle generation unit and a dead zone compensation unit;

[0032] The duty cycle generation unit generates a PWM drive signal with a corresponding duty cycle based on the control quantity output by the PID adjustment module through a timer comparison matching method.

[0033] The dead-time compensation unit inserts a fixed-length dead time when the power transistor switches between the upper and lower bridge arms, and dynamically adjusts the conduction time to compensate for the voltage loss caused by the dead time.

[0034] Preferably, the PID control module includes a deviation calculation unit, a PID calculation and anti-saturation unit, and a parameter smoothing switching unit;

[0035] The deviation calculation unit calculates the real-time deviation between the target speed command value and the Hall speed feedback value;

[0036] The PID calculation and anti-saturation unit multiplies the deviation by a proportional coefficient, accumulates and integrates the deviation, performs differential calculation on the deviation, and sums the three to obtain the duty cycle control quantity. When the duty cycle control quantity exceeds the maximum allowable value of PWM, the integration and accumulation are stopped to prevent saturation.

[0037] The parameter smoothing switching unit selects a corresponding set from at least three pre-stored PID parameters based on the material type and load trend signal output by the load state judgment terminal, and uses a linear transition to make the current PID parameter gradually approach the target parameter; when a change in load level from light load to heavy load and a change in material type are detected, the current PID parameter and the target PID parameter are weighted and fused, and the weighting coefficient increases from 0 to 1 according to a preset step value, with the switching completion time being 10 milliseconds to 200 milliseconds.

[0038] Preferably, the inertial start protection module includes an overcurrent detection unit, a mode switching unit, and a dynamic torque limiting unit;

[0039] The overcurrent detection unit compares the real-time current value with the hardware overcurrent threshold through a comparator. When the current exceeds the threshold, it directly outputs a hardware blocking signal to force the PWM output low in order to protect the power device.

[0040] The mode switching unit automatically selects three pre-stored PID parameters to start operation based on the load level code output by the load status judgment terminal.

[0041] The dynamic torque limiting unit calculates the maximum allowable output torque limit in real time based on the material type and load trend output by the load state judgment terminal. In concrete mode, the maximum allowable torque limit is 80% of the rated torque; in steel mode, the maximum allowable torque limit is 120% of the rated torque; and in wood mode, the maximum allowable torque limit is 100% of the rated torque.

[0042] The present invention has the following beneficial effects:

[0043] 1. In this invention, the load sensing end monitors the magnitude and rate of change of the working current of the electric hammer in real time, and simultaneously collects the vibration intensity of the housing axial direction. When a sudden and significant change in current is detected, a rapid response signal is immediately sent to the subsequent judgment stage, thereby improving the system's judgment speed and shortening the stable judgment time. In addition, by performing spectrum analysis on the vibration signal, when an abnormally high second harmonic of the impact frequency is found, accompanied by repeated and violent fluctuations in current, the drill bit slippage state can be accurately identified. This allows the electric hammer to quickly sense and distinguish between normal impact and abnormal slippage at the moment the load impact occurs, shortening the delay time from load change to system response and avoiding drill jamming or motor overload caused by response lag.

[0044] 2. In this invention, the load status judgment terminal compares the real-time measured current value with the pre-stored multi-level current range step by step to accurately determine whether the current is in a light load, medium load, heavy load, or stall state; it integrates the three characteristics of current magnitude, current change rate, and vibration amplitude into a three-dimensional judgment criterion, and matches it with the standard characteristics of materials such as concrete, steel, and wood to identify the current drilling material type; by analyzing the slope of change and cumulative trend of multiple consecutive current sampling points, it can predict in advance whether the load is increasing or decreasing, so that the system can predict the change of working condition before material switching or load gradual change occurs, providing a control basis for subsequent speed adjustment, and avoiding misjudgment or response lag caused by traditional single threshold judgment.

[0045] 3. In this invention, the speed and torque control terminal automatically selects matching PID control parameters based on the load level and material type given by the load state judgment terminal. When the load or material changes, the parameters are not switched by instantaneous jumps, but rather the current parameters are linearly and smoothly transitioned to the target parameters within 10 to 200 milliseconds, and the weights are gradually adjusted, thereby eliminating the speed and torque shocks caused by parameter abrupt changes. At the same time, based on the identified different materials such as concrete, steel, and wood, the maximum torque that the motor can output is dynamically limited, set to 80%, 120%, and 100% of the rated torque, respectively. This ensures that the electric hammer can obtain sufficient drilling force without overloading and damage when drilling different materials. During load switching, the speed and output torque change smoothly, improving drilling accuracy and operating comfort. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the overall system architecture of an electric hammer adaptive load speed regulation control system according to the present invention;

[0047] Figure 2 This is a schematic diagram of the load sensing end of an adaptive load speed control system for electric hammers according to the present invention.

[0048] Figure 3 This is a schematic diagram of the load state judgment terminal of an electric hammer adaptive load speed regulation control system according to the present invention.

[0049] Figure 4 This is a schematic diagram of the speed and torque control terminal of an electric hammer adaptive load speed regulation control system according to the present invention. Detailed Implementation

[0050] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0051] Example 1, please refer to Figures 1-2 As shown: An adaptive load speed control system for electric hammers, the system includes a load sensing terminal, a load status judgment terminal, and a speed and torque control terminal;

[0052] The load sensing end is used to collect the current waveform and the axial vibration spectrum of the shell during the operation of the electric hammer in real time, extract the effective value of the current, the rate of change of the current and the amplitude of the axial vibration, and send the fast response mode trigger signal to the load status judgment end.

[0053] The load status judgment end is used to determine the current load level by comparing the received current effective value with the preset threshold range and output the load level code. It identifies the material type based on the three-dimensional feature vector composed of the current effective value, current change rate and axial vibration amplitude. At the same time, it predicts the load change trend by calculating the slope and integral value of the current sampling value and outputs a set of control parameters containing the target speed command.

[0054] The speed and torque control terminal performs closed-loop regulation through the PID adjustment module based on the control parameter set, which enables the PWM modulation module to generate a drive signal. The inertial start protection module realizes overcurrent protection, mode switching and torque limiting, so as to adaptively control the speed and output torque of the electric hammer motor.

[0055] The load sensing end includes a current sampling module, a vibration detection module, and a speed feedback module;

[0056] The current sampling module includes a current RMS value unit and a current change rate unit;

[0057] The current RMS value unit uses a sliding window root mean square algorithm to calculate the RMS current value within one power frequency cycle to characterize the steady-state load magnitude. In specific implementation:

[0058] The system uses a Hall current sensor to collect the instantaneous phase current value of the electric hammer motor in real time at a sampling frequency of 10kHz. Assuming one power frequency cycle is 20ms, corresponding to 200 sampling points, these 200 consecutive sampling points form a sliding window. Each time a new sampling point is added, the oldest point in the window is removed, keeping the window length fixed. The squares of all instantaneous current values ​​within the window are summed, the average value is calculated, and then the square root is taken. The calculation formula is as follows:

[0059] ;

[0060] in, This represents the effective value of the current at the current moment. This represents the number of sampling points within the sliding window (200 in this example). The nth instantaneous current sample value within the window is used to calculate the effective current value, which is updated every two sampling points (i.e., 0.2ms). This value is used to characterize the steady-state load of the electric hammer in the most recent power frequency cycle. The effective value is output to the load status judgment terminal in real time as the basis for judging light load, medium load, heavy load and stall.

[0061] The current change rate unit calculates the ratio of the current increment to the time interval between adjacent sampling points using a differential algorithm. When this ratio exceeds a preset sudden change threshold, a load transient impact flag is output, which triggers the load status judgment terminal to enter a fast response mode. In fast response mode, the comparison period of the interval decision unit of the load status judgment terminal is shortened to 1 / 4 of the normal period, and the time threshold of the integral decision unit of the trend prediction module is reduced to 1 / 3 of the normal value. Specifically:

[0062] The system acquires the instantaneous current values ​​at two consecutive sampling times using the same sampling frequency (10kHz) as the current RMS value unit, and calculates the rate of change of current using a first-order forward difference formula:

[0063] ;

[0064] in, Let the current value be at the k-th sampling time. The current value at the next sampling time. The time interval between two adjacent samples (0.0001 seconds in this embodiment) is used to calculate the current change rate in amperes per second. The system pre-stores a sudden change threshold (e.g., 2000 A / s) in its memory. This threshold is obtained through experimental calibration and represents the typical minimum current change rate when the electric hammer suddenly comes into contact with a hard material from no load. When the real-time calculated current change rate exceeds this threshold, the unit outputs a high-level transient impact flag signal. This signal is immediately sent to the load state judgment terminal, triggering it to enter the fast response mode. In the fast response mode, the comparison period of the interval decision unit of the load state judgment terminal is shortened to 1 / 4 of the normal period (e.g., from 40ms to 10ms), and the time threshold of the integral decision unit of the trend prediction module is reduced to 1 / 3 of the normal value (e.g., from 300ms to 100ms) to achieve a fast response to transient changes in the load.

[0065] The vibration detection module includes an axial vibration unit and a rotational speed and frequency extraction unit;

[0066] The axial vibration unit acquires the axial impact vibration amplitude of the hammer shaft head through a piezoelectric accelerometer, and extracts the DC component of the impact energy after filtering. In specific implementation:

[0067] A piezoelectric accelerometer is rigidly fixed to the hammer housing near the drill bit axis, with the sensor's sensing direction aligned with the drill bit's axis. The sensor's output charge signal is converted into a voltage signal by a charge amplifier, with the voltage amplitude proportional to the axial acceleration. This signal first passes through a low-pass filter with a cutoff frequency of 500Hz to remove high-frequency noise interference, and then through a low-pass filter with a cutoff frequency of 10Hz for smoothing. The DC component of the impact vibration amplitude is then extracted, and the formula for calculating this DC component is as follows:

[0068] ;

[0069] in, This represents the instantaneous value of the axial acceleration. The integration time window is 0.1 seconds in this embodiment. The DC component of the impact energy represents the average intensity of the axial impact of the electric hammer. This DC component is output in real time to the material identification module at the load state judgment end, and together with the effective value of the current and the rate of change of the current, it forms a three-dimensional feature vector.

[0070] The rotational speed and frequency extraction unit converts the time-domain vibration signal into a frequency-domain spectrum using a fast Fourier transform, extracting the harmonic amplitudes corresponding to the electric hammer impact frequency and its harmonics. The harmonic amplitudes are compared with reference amplitudes under normal operating conditions. If the second harmonic amplitude exceeds 60% of the fundamental amplitude and is accompanied by the current change rate repeatedly exceeding the abrupt change threshold, it is determined to be a slippage state of the toothed teeth, and this state is encoded and sent to the load state judgment terminal. Specifically:

[0071] The system continuously acquires the raw acceleration signal (without low-pass filtering) output by the axial vibration unit at a sampling frequency of 2kHz. 1024 points are acquired every 0.5 seconds to form a data frame. A Hanning window is applied to this data frame to reduce spectral leakage, and then a fast Fourier transform is performed to obtain the spectral distribution from 0 to 1kHz. The amplitude of the fundamental frequency component corresponding to the current impact frequency of the electric hammer is extracted from the spectrum. and the amplitude of its second harmonic (2 times the impulse frequency). The impact frequency is obtained by converting the real-time motor speed provided by the speed feedback module through the reduction ratio. The known reduction ratio is... Then the impact frequency ,in The system is pre-calibrated and has saved the fundamental amplitude reference value under normal operating conditions (no slippage, drill bit in good condition). and second harmonic amplitude reference value Under normal circumstances, the amplitude of the second harmonic is approximately 20-40% of the fundamental amplitude; during implementation, the measured amplitude will be... and A comparison is made, and if the following two conditions are met, the toother is determined to be slipping: First, First, the amplitude of the second harmonic exceeds 60% of the fundamental amplitude. Second, within the last 0.5 seconds, the transient impact flag output by the current change rate unit has appeared at least 3 times, that is, the current change rate repeatedly exceeds the sudden change threshold. When both conditions are met, the unit outputs a tooth slippage status code (e.g., hexadecimal 0x01) and sends the code to the load status judgment terminal for it to adjust the subsequent control strategy (such as reducing the target speed or limiting the upper limit of torque to prevent further slippage and damage to the drill bit).

[0072] The speed feedback module includes a Hall pulse counting unit and a speed conversion unit;

[0073] The Hall pulse counting unit detects the pulse signal output by the motor in real time when it rotates through a Hall sensor at the tail end of the motor, and uses a timer to measure the time interval between adjacent pulses. Specifically:

[0074] A multi-pole magnetic ring with a 6-pole configuration is mounted on the motor's tail shaft. This means that a Hall sensor outputs 6 pulses for every revolution of the motor. The square wave pulse signal output by the Hall sensor is connected to the capture input pin of the microcontroller. The microcontroller internally uses a 32-bit timer operating in capture mode with a clock frequency set to 1MHz and a timing resolution of 1 microsecond. Each time a rising edge of a pulse is detected, the timer automatically captures the current count value and generates an interrupt. In the interrupt service routine, the difference between the current and previous captured values ​​is read. This difference is multiplied by the timing resolution (1 microsecond) to obtain the time interval between adjacent pulses. The unit is seconds. Because a 32-bit timer is used, the maximum count value is approximately 4.29 billion, corresponding to a maximum measurable time interval of approximately 4290 seconds. This is sufficient to cover the entire range of the motor from its highest speed to complete stop, eliminating the need for additional overflow handling. When the motor is stationary, no pulses are generated, and the timer will not trigger a capture interrupt. In this case, the software determines that the motor is stationary if no pulse is received within a preset time (e.g., 0.5 seconds). Set it to infinity.

[0075] The speed conversion unit calculates the current actual speed value based on the number of pulses per motor revolution using a frequency-speed conversion formula. This value is then used as feedback in closed-loop control. Simultaneously, the actual speed value is fed back to the load status judgment terminal and the speed-torque control terminal. In specific implementation:

[0076] Let the time interval between adjacent pulses be . (Unit: seconds), then the pulse frequency (Unit: Hz) Number of pulses output per revolution of the motor Determined by the number of magnetic pole pairs, in this embodiment actual speed The formula for calculating (unit: revolutions per minute) is:

[0077] ;

[0078] Substituting P=6, we get: For example, when the interval between adjacent pulses is measured... At that time, the calculation yielded To prevent sudden changes in the measured speed due to noise or pulse loss, a first-order low-pass filter is applied to the calculated speed value: , where the filter coefficients Taking 0.1, the filtered actual speed value is output as feedback to the PID control module of the speed and torque control terminal, used to compare with the target speed command value to generate a deviation signal; on the other hand, it is sent to the load state judgment terminal for reference by the trend prediction module and the material identification module. When the motor is stationary ( When the value is infinite, the actual rotational speed is forced to be 0.

[0079] Example 2, please refer to Figure 3 As shown: The load status determination terminal includes a load comparison module, a material identification module, and a trend prediction module;

[0080] The load comparison module includes a threshold storage unit and an interval decision unit;

[0081] The threshold storage unit pre-stores the current threshold ranges of the electric hammer under different operating voltages (light load, medium load, heavy load, and stall) in non-volatile memory. In specific implementation:

[0082] During the factory calibration phase of the electric hammer product, the no-load current, light-load drilling current, medium-load drilling current, heavy-load drilling current, and stall current are measured under rated voltage (e.g., 220V) and common voltage fluctuation ranges (e.g., 187V-242V). The measured current values ​​are stored in the microcontroller's non-volatile memory (e.g., Flash or EEPROM) in the form of intervals. Each load level corresponds to a lower current threshold and an upper current threshold. For example, the light-load interval corresponds to the effective current value. ; corresponding to the intermediate load interval Heavy load interval corresponding to The corresponding blocking section To accommodate different operating voltages, a three-dimensional table is stored, with indices for voltage level (e.g., low voltage, normal voltage, high voltage) and load level. Each cell stores the corresponding threshold boundary value. When the electric hammer is powered on, the system first detects the current input voltage and selects a corresponding set of threshold intervals based on the voltage value.

[0083] The interval decision unit compares the current measured effective current value with the threshold interval step by step using a numerical comparator. If the current exceeds the stall threshold, a stall flag signal is output; otherwise, the corresponding load level digital code is output. When a fast response mode trigger signal is received from the load sensing end, the comparison cycle is shortened to 1 / 4 of the normal cycle. In specific implementation:

[0084] The interval decision unit acquires the output of the current effective value unit at a fixed period. In normal operating mode, the comparison period is set to 40ms (i.e., 25 comparisons per second). The following comparison operations are performed sequentially within the unit: First, determine... Is it greater than or equal to the lower limit threshold of stall? If yes, then directly output the stall flag signal (e.g., encoded 0x04) and immediately stop subsequent comparisons; if not, then determine... Is it less than the light load upper limit threshold? If yes, output the light-load code (0x00); otherwise, determine... Is it less than the upper limit threshold of the medium load? If yes, output the load code (0x01); otherwise, determine... Is it less than the overload upper limit threshold? If yes, output overload code (0x02); if neither is satisfied, output stall code (0x03). While outputting the load level digital code, this code is sent to the mode switching unit at the speed and torque control end to select the corresponding PID parameter group. When the interval decision unit receives the fast response mode trigger signal from the load sensing end, it automatically shortens the comparison period from 40ms to 10ms (i.e., 1 / 4 of the normal period), while other judgment logic remains unchanged, in order to achieve a faster response to transient load changes.

[0085] The material identification module includes a current and vibration combined feature unit and a lookup table discrimination unit;

[0086] The current and vibration combined feature unit synchronously acquires the effective value of the current, the rate of change of the current, and the axial vibration amplitude, and normalizes the three to form a three-dimensional feature vector. In specific implementation:

[0087] The unit synchronously reads three data sources with a period of 20ms (i.e., every two power frequency cycles): obtaining the current effective value from the current unit. Obtain the absolute value of the average rate of change over the most recent period from the current rate of change unit. Obtain the DC component of impact energy from the axial vibration unit. Since the three physical quantities have different dimensions and ranges, they need to be normalized separately. The normalization uses a linear mapping formula:

[0088] ;

[0089] in, These are the original measured values. and These are the minimum and maximum values ​​of the physical quantity within its normal operating range, respectively. The normalized value (ranging from 0 to 1); specifically, The calibration range is 0-30A. The calibration range is 0-5000 A / s. The calibration range is 0-5V (voltage after charge amplifier), and after normalization, three components are obtained: , , Arrange these three components in a fixed order to form a three-dimensional feature vector. The vector is output to the lookup table discrimination unit in real time.

[0090] The lookup table discrimination unit performs nearest neighbor matching between the three-dimensional feature vector and the pre-stored standard feature vectors of different materials, outputting the material type of the current structure. When the nearest neighbor distance between the three-dimensional feature vector and the pre-stored standard feature vector exceeds a set threshold, an unknown material flag is output, and the control parameter set is automatically set to the medium load balance parameter. At the same time, the current change rate threshold is temporarily increased by 20% to reduce the risk of misjudgment. In specific implementation:

[0091] The unit's internal non-volatile memory pre-stores three sets of standard feature vectors, corresponding to concrete, steel, and wood, respectively. These standard vectors were obtained through experimental calibration: under the same hammer drill and rotation speed conditions, holes were drilled in the three standard specimens, and a large number of feature vectors were collected and averaged. The standard vector for each material is denoted as follows: , , For the current input measured feature vector Calculate its Euclidean distance to each of the three standard vectors:

[0092] ;

[0093] ;

[0094] in , and The first The normalized components of the effective value of current, rate of change of current, and axial vibration amplitude in the standard eigenvector of a certain material. , and Let concrete, steel, and wood be represented respectively. Find the smallest value. Let the minimum distance be . The corresponding material type is Preset a distance threshold (In this embodiment, 0.35 is used. Experiments are conducted to ensure that the distance between different material types is greater than this threshold, while the internal distance between materials of the same type is less than this threshold); If Then output material type (e.g., concrete code 0x10, steel code 0x11, timber code 0x12), and send this code to the parameter smoothing switching unit and dynamic torque limiting unit at the speed torque control end; if This indicates that the current feature vector differs significantly from all pre-stored standard vectors, potentially indicating the presence of unknown materials (such as bricks, ceramic tiles, or composite materials). In this case, the unit outputs an unknown material flag (0xFF) and automatically sets the control parameter set to medium-load balance parameters (i.e., the target speed and torque are output at medium-load levels, and the corresponding PID parameters are selected from the medium-load balance group). Simultaneously, to improve the system's stability under unknown materials, the sudden change threshold of the current change rate unit is temporarily increased by 20% (e.g., from 2000A / s to 2400A / s) to avoid frequent triggering of the fast response mode due to irregular current fluctuations caused by unknown materials, which could lead to malfunctions. This temporary threshold adjustment takes effect immediately after the unknown material flag is output and remains at the default value until the user releases the switch or the system is powered on again.

[0095] The trend prediction module includes a slope calculation unit and an integral decision unit;

[0096] The slope calculation unit calculates the slope of the most recent N current samples over time using the least squares method. If the slope is positive and greater than the rising threshold, the load is judged to be overloaded; if the slope is negative and the absolute value is greater than the falling threshold, the load is judged to be lightened. In specific implementation:

[0097] The cell obtains an RMS current value from the current RMS value cell at fixed time intervals (e.g., every 10ms). The most recent N data points are cached (in this embodiment, N=10, corresponding to the most recent 100ms), and each data point contains a time index. ( (unit: ms) and the corresponding current value A straight line is fitted using the least squares method. The slope The calculation formula is:

[0098] ;

[0099] The calculated slope k is expressed in amperes per second (A / s), representing the rate of change of current. ,in If the load is set to an increasing threshold (20 A / s in this embodiment), then it is determined that the load is trending towards heavier load, and a load-heavy indicator is output; if ,in If the load is set to a decreasing threshold (15A / s in this embodiment), it is determined that the load is becoming lighter, and a load lightening flag is output. If k is between the two values, the load trend is considered to be insignificant, and a load stabilization flag is output. These flags are sent to the parameter smoothing switching unit at the speed and torque control end to adjust the direction of change of the PID parameters in advance.

[0100] The integral decision unit integrates multiple consecutive slope values. When the integral value exceeds a predetermined time threshold, it outputs a load state stabilization signal to suppress misjudgments caused by transient disturbances. In fast response mode, the time threshold is reduced to 1 / 3 of the normal value. Specifically, in implementation:

[0101] The unit receives the slope at the same period (10ms) as the slope calculation unit. The real-time value is integrated (i.e., accumulated) over a continuous period of time, and the integral value is set as follows: ,in The sampling interval is 0.01 seconds. For the first The slope calculated each time, and the integration window length corresponds to a predetermined time threshold. In normal mode Take 300ms, that is, accumulate the most recent 30 slope values. If the accumulated integral value S exceeds a preset stability threshold... (For example, 100A) If the load condition is stable, a load condition stabilization signal is output, indicating that the load has been changing in a certain direction for a sufficient period of time, and the current trend can be considered real rather than a momentary disturbance. Conversely, if the integral value does not exceed the threshold, no stabilization signal is output, and the system continues to maintain a fast response capability. In fast response mode, the time threshold of the integral decision unit is reduced to 1 / 3 of the normal value (i.e., 100ms). At this time, only the most recent 10 slope values ​​are accumulated, so that the system can confirm the load trend change more quickly. After outputting the load condition stabilization signal, the signal is sent to the speed and torque control terminal to confirm that the PID parameters can complete the switching and lock the new parameter group, avoiding repeated parameter switching due to short-term disturbances.

[0102] Example 3, please refer to Figure 4 As shown: The speed and torque control module includes a PWM modulation module, a PID adjustment module, and an inertial start protection module;

[0103] The PWM modulation module includes a duty cycle generation unit and a dead-time compensation unit;

[0104] The duty cycle generation unit generates a PWM drive signal with the corresponding duty cycle based on the control quantity output by the PID control module through a timer comparison matching method. Specifically:

[0105] The microcontroller's timer operates in center-aligned PWM mode, with a timer clock frequency of 20MHz and a counting period of 1000 (i.e., the count value counts from 0 to 1000 and then back to 0). The corresponding PWM switching frequency is 10kHz. The control quantity U (range 0-1000, dimensionless) output by the PID control module is directly stored as a comparison value in the timer's compare register. When the timer count value is less than the compare register value, a high level is output; when it is greater, a low level is output. The actual duty cycle D is calculated using the following formula:

[0106] ;

[0107] in For the target comparison value, For example, duty cycle percentage At this time, the duty cycle is 60%. The timer generates two matching events in each PWM cycle. The drive signal is sent to the power transistor driver chip after being inserted through the dead time. At the same time, two complementary PWM signals are generated to control the upper and lower bridge arms respectively.

[0108] The dead-time compensation unit inserts a fixed-length dead time when the power transistor switches between the upper and lower bridge arms, and dynamically adjusts the conduction time to compensate for the voltage drop caused by the dead time. In practice:

[0109] Set dead time length (To prevent shoot-through between upper and lower bridge arms) When the PWM signal of the upper bridge arm switches from high to low and the signal of the lower bridge arm switches from low to high, insert... The delay causes both bridge arms to be in the off state. Dead-time insertion results in the average voltage actually applied to the motor being lower than the theoretical value. To compensate for this loss, dynamic on-time compensation is used, based on the current duty cycle. (Value range 0-1) and target dead time Calculate the conduction time that requires additional compensation. (Unit: seconds):

[0110] ;

[0111] in, , Given the current duty cycle (0-1), when Maximum compensation amount (time) );when When the value approaches 0 or 1, the compensation amount approaches 0. To convert the compensation time into an increment of the PWM comparison value, the timer counting frequency is used. (i.e., 20 counts per microsecond), calculate the increment of the compensation comparison value. (Dimensionless):

[0112] ;

[0113] For example, when hour , The actual value written to the compare register is ,in The compensation is calculated and updated every half PWM cycle as the original comparison value of the PID output, thereby maintaining voltage output linearity while ensuring safety.

[0114] The PID control module includes a deviation calculation unit, a PID calculation and anti-saturation unit, and a parameter smoothing switching unit;

[0115] The deviation calculation unit calculates the real-time deviation between the target speed command value and the Hall speed feedback value. In specific implementation:

[0116] The unit receives the target speed command value from the load status judgment terminal. (Unit: revolutions per minute), and simultaneously obtain the actual speed feedback value from the speed feedback module. Real-time deviation The calculation formula is:

[0117] ;

[0118] in, A positive value indicates that the current speed is lower than the target value and acceleration is required; a negative value indicates that the speed is higher than the target value and deceleration is required. This deviation value is calculated every 10ms and used as input for PID calculation and anti-saturation unit.

[0119] The PID calculation and anti-saturation unit multiplies the deviation by a proportional coefficient, integrates and accumulates the deviation, and performs differential and derivative operations on the deviation. The sum of these three operations yields the duty cycle control value. When the duty cycle control value exceeds the maximum allowable value of the PWM, the integration and accumulation stops to prevent saturation. In specific implementation:

[0120] The unit uses a positional PID algorithm to control the quantity. The calculation formula is:

[0121] ;

[0122] in, , , These are the proportional, integral, and derivative coefficients, respectively (provided by the parameter smoothing switching unit). The sampling period is 0.01 seconds. The summation term is the cumulative integral of the deviation, and the last term is the differential of the deviation. The calculated... This represents the comparison value (range 0-1000) corresponding to the desired PWM duty cycle; to prevent integral saturation, the comparison value is calculated each time. Then, determine whether it exceeds the valid range [0, 1000]: If Then The clamp is set to 1000, and the accumulation of the integral term is stopped (i.e., the deviation is not accumulated this time); if Then If the clamp is 0, the integration will also stop; if If within the range, the integral is accumulated normally, and the control quantity after clamping is... The duty cycle is output to the duty cycle generation unit of the PWM modulation module.

[0123] The parameter smoothing switching unit selects a corresponding set of PID parameters from at least three pre-stored sets based on the material type and load trend signal output from the load status judgment terminal, and uses a linear transition to gradually approach the target parameter with the current PID parameter. When a change in load level from light load to heavy load or a change in material type is detected, the current PID parameter and the target PID parameter are weighted and fused, with the weighting coefficient increasing from 0 to 1 according to a preset step value. The switching completion time is 10 milliseconds to 200 milliseconds. In specific implementation:

[0124] Three sets of PID parameters are pre-stored in the non-volatile memory: light load high speed group ( , , ), medium load balancing group ( , , ), heavy-duty high-torque group ( , , Furthermore, parameters are fine-tuned within the same load level depending on the material type (concrete, steel, wood), for example, the parameters are appropriately reduced in the concrete mode. To suppress impact oscillations, the steel material mode should be appropriately increased. To enhance steady-state stiffness; when the load level code or material type code output by the load state judgment terminal changes, the parameter smoothing switching unit determines the target parameter set. And record the parameter group currently in use. Set switching time The time step is automatically selected between 10ms and 200ms based on the severity of load changes (e.g., 50ms for light to medium load, 100ms for medium to heavy load, and 150ms for material type change), and the number of steps is set. ( ), weighting coefficient Starting from 0, after each sampling period, Increase The actual parameters for operation are:

[0125] ;

[0126] and Similarly, linear interpolation is performed when... When the switch is complete, the parameters are fixed at the target value. If a change in load level or material type is detected during the switch, the current transition is interrupted, and the system restarts the transition to the new target parameters from the current actual parameters, ensuring that the system always responds quickly to changes in operating conditions without any shock.

[0127] The inertial start protection module includes an overcurrent detection unit, a mode switching unit, and a dynamic torque limiting unit;

[0128] The overcurrent detection unit compares the real-time current value with the hardware overcurrent threshold using a comparator. When the current exceeds the threshold, it directly outputs a hardware blocking signal, forcibly pulling the PWM output low to protect the power device. In specific implementation:

[0129] A milliohm-level sampling resistor (e.g., ...) is connected in series in the power supply circuit of the electric hammer motor. The differential amplifier amplifies the voltage across the resistor and sends it to the analog comparator input of the microcontroller. The other input of the comparator is connected to a hardware-set overcurrent threshold voltage, which corresponds to twice the rated current of the motor (e.g., a rated current of 15A corresponds to a threshold of 30A). The comparator output is directly connected to the enable pin of the PWM driver and the external interrupt pin of the microcontroller. When the real-time current exceeds the threshold, the comparator output level flips, and the hardware-level blocking signal forces the PWM drive signal low within 1 microsecond, turning off all power transistors. At the same time, it triggers the microcontroller interrupt to record the fault status. This protection is entirely implemented by hardware and does not depend on the software response time, ensuring that the power devices are protected in time during short circuits or severe overloads.

[0130] The mode switching unit automatically selects one of the three pre-stored PID parameters for operation based on the load level code output by the load status judgment terminal. Specifically, in implementation:

[0131] The unit receives the load level digital code (light load 0x00, medium load 0x01, heavy load 0x02, stalled 0x03) from the load comparison module; the unit internally stores three sets of PID parameters: light load high speed group ( , , ), medium load balancing group ( , , ), heavy-duty high-torque group ( , , According to the code, the unit automatically selects the corresponding parameter group: when receiving a light load code, it sends the light load parameter group to the parameter smoothing switching unit of the PID control module as the target parameter; when receiving a medium load code, it sends the medium load parameter group; when receiving a heavy load code, it sends the heavy load parameter group; when receiving a stall code, the unit not only selects the heavy load high torque parameter group, but also outputs an additional stall flag bit to the dynamic torque limiting unit, indicating that the upper limit of torque is temporarily increased to 150% of the rated torque to try to overcome the stall. If the stall is not relieved within 500ms, the original limit is restored and an alarm is triggered.

[0132] The dynamic torque limiting unit calculates the maximum allowable output torque in real time based on the material type and load trend at the load condition judgment terminal. In concrete mode, the maximum allowable torque is 80% of the rated torque; in steel mode, it is 120% of the rated torque; and in wood mode, it is 100% of the rated torque. In specific implementation:

[0133] The unit obtains the material type code (concrete 0x10, steel 0x11, wood 0x12, unknown material 0xFF) from the material identification module, the load level code from the load comparison module, and the load trend indicator and rated torque from the trend prediction module. The maximum permissible torque is determined by the motor's rated parameters (10 Nm in this example). The calculation formula is:

[0134] ;

[0135] in, Material coefficients: concrete 0.8, steel 1.2, timber 1.0, unknown material 1.0 (medium load balance); Load trend adjustment factor: 1.1 when the load trend is towards heavier load and stall has not occurred; otherwise, 1.0. For example, in steel mode and when a heavier load is detected, (132% of rated torque); the unit will calculate in real time The signal is sent to the PID control module and PWM modulation module to limit the maximum output of the duty cycle. The specific limit is achieved by modifying the upper limit of the control quantity in the PID calculation and anti-saturation unit, that is, judging whether it is close to the current torque estimate (estimated by current and speed). If the torque is close, the duty cycle will not be increased further. In addition, in concrete mode, appropriately reducing the torque helps to prevent the impact reaction force from injuring the operator when the drill bit is stuck. In steel mode, short-term over-torque is allowed to improve the drilling penetration capability.

[0136] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An adaptive load speed control system for an electric hammer, characterized in that, The system includes a load sensing terminal, a load status judgment terminal, and a speed and torque control terminal; The load sensing end is used to collect the current waveform and the axial vibration spectrum of the shell during the operation of the electric hammer in real time, extract the effective value of the current, the rate of change of the current and the amplitude of the axial vibration, and send the fast response mode trigger signal to the load status judgment end. The load status judgment terminal is used to determine the current load level by comparing the received current effective value with a preset threshold range and output the load level code. It identifies the material type based on the three-dimensional feature vector composed of the current effective value, current change rate and axial vibration amplitude. At the same time, it predicts the load change trend by calculating the slope and integral value of the current sampling value and outputs a set of control parameters containing the target speed command. The speed and torque control terminal performs closed-loop regulation through the PID adjustment module based on the control parameter set, so that the PWM modulation module generates a drive signal, and the inertial start protection module realizes overcurrent protection, mode switching and torque limiting, so as to adaptively control the speed and output torque of the electric hammer motor.

2. The adaptive load speed control system for an electric hammer according to claim 1, characterized in that, The load sensing terminal includes a current sampling module, a vibration detection module, and a speed feedback module; The current sampling module includes a current effective value unit and a current change rate unit; The current RMS value unit uses the sliding window root mean square algorithm to calculate the current RMS value within one power frequency cycle to characterize the steady-state load size; The current change rate unit calculates the ratio of the current increment to the time interval between adjacent sampling points using a differential algorithm. When the ratio exceeds a preset sudden change threshold, a load transient impact flag is output, and the transient impact flag is used to trigger the load status judgment terminal to enter the fast response mode. In the fast response mode, the comparison period of the interval decision unit of the load status judgment terminal is shortened to 1 / 4 of the normal period, and the time threshold of the integral decision unit of the trend prediction module is reduced to 1 / 3 of the normal value.

3. The adaptive load speed control system for an electric hammer according to claim 2, characterized in that, The vibration detection module includes an axial vibration unit and a rotational speed and frequency extraction unit. The axial vibration unit collects the axial impact vibration amplitude of the hammer shaft head through a piezoelectric accelerometer, and extracts the DC component of the impact energy after filtering. The rotational speed and frequency extraction unit converts the time-domain vibration signal into a frequency-domain spectrum through a fast Fourier transform, extracts the harmonic amplitude corresponding to the electric hammer impact frequency and its harmonics, compares the harmonic amplitude with the reference amplitude under normal operating conditions, and if the second harmonic amplitude exceeds 60% of the fundamental amplitude and the current change rate repeatedly exceeds the sudden change threshold, it is determined to be a slipping state of the toothed tooth, and the state code is sent to the load state judgment terminal.

4. The adaptive load speed control system for an electric hammer according to claim 2, characterized in that, The speed feedback module includes a Hall pulse counting unit and a speed conversion unit; The Hall pulse counting unit detects the pulse signal output by the motor in real time when the motor rotates through the Hall sensor at the tail end of the motor, and uses a timer to measure the time interval between adjacent pulses. The speed conversion unit calculates the current actual speed value based on the number of pulses corresponding to each revolution of the motor using the frequency-speed conversion formula. This value is used as feedback to participate in closed-loop control, and the actual speed value is simultaneously fed back to the load status judgment terminal and the speed-torque control terminal.

5. The adaptive load speed control system for an electric hammer according to claim 1, characterized in that, The load status determination terminal includes a load comparison module, a material identification module, and a trend prediction module; The load comparison module includes a threshold storage unit and an interval decision unit; The threshold storage unit pre-stores the current threshold ranges of the electric hammer under different working voltages (light load, medium load, heavy load, and stall) through a non-volatile memory. The interval decision unit compares the current measured effective value of the current with the threshold interval step by step through a numerical comparator. If the current exceeds the stall threshold, a stall flag signal is output; otherwise, a digital code corresponding to the load level is output. When a fast response mode trigger signal is received from the load sensing end, the comparison cycle is shortened to 1 / 4 of the normal cycle.

6. The adaptive load speed control system for an electric hammer according to claim 5, characterized in that, The material identification module includes a current and vibration combined feature unit and a lookup table discrimination unit; The current and vibration combined feature unit synchronously collects the effective value of current, the rate of change of current and the amplitude of axial vibration, and normalizes the three to form a three-dimensional feature vector. The lookup and discrimination unit performs nearest neighbor matching between the three-dimensional feature vector and the pre-stored standard feature vectors of different materials, outputs the material type of the current structure, and outputs an unknown material flag when the nearest neighbor distance between the three-dimensional feature vector and the pre-stored standard feature vector exceeds a set threshold. It also automatically sets the control parameter set to the medium load balance parameter and temporarily increases the current change rate threshold by 20% to reduce the risk of misjudgment.

7. The adaptive load speed control system for an electric hammer according to claim 5, characterized in that, The trend prediction module includes a slope calculation unit and an integral decision unit; The slope calculation unit calculates the slope value of the most recent N current sampling values ​​over time using the least squares method. If the slope is positive and greater than the rising threshold, it is determined that the load is overloaded. If the slope is negative and the absolute value is greater than the falling threshold, it is determined that the load is becoming lighter. The integral decision unit accumulates and integrates multiple consecutive slope values. When the integral value exceeds a predetermined time threshold, it outputs a load state stabilization signal to suppress misjudgments caused by instantaneous disturbances. In fast response mode, the time threshold is reduced to 1 / 3 of the normal value.

8. The adaptive load speed control system for an electric hammer according to claim 1, characterized in that, The speed and torque control terminal includes a PWM modulation module, a PID adjustment module, and an inertial start protection module; The PWM modulation module includes a duty cycle generation unit and a dead zone compensation unit; The duty cycle generation unit generates a PWM drive signal with a corresponding duty cycle based on the control quantity output by the PID adjustment module through a timer comparison matching method. The dead-time compensation unit inserts a fixed-length dead time when the power transistor switches between the upper and lower bridge arms, and dynamically adjusts the conduction time to compensate for the voltage loss caused by the dead time.

9. The adaptive load speed control system for an electric hammer according to claim 8, characterized in that, The PID control module includes a deviation calculation unit, a PID calculation and anti-saturation unit, and a parameter smoothing switching unit. The deviation calculation unit calculates the real-time deviation between the target speed command value and the Hall speed feedback value; The PID calculation and anti-saturation unit multiplies the deviation by a proportional coefficient, accumulates and integrates the deviation, performs differential calculation on the deviation, and sums the three to obtain the duty cycle control quantity. When the duty cycle control quantity exceeds the maximum allowable value of PWM, the integration and accumulation are stopped to prevent saturation. The parameter smoothing switching unit selects a corresponding set from at least three pre-stored PID parameters based on the material type and load trend signal output by the load state judgment terminal, and uses a linear transition to make the current PID parameter gradually approach the target parameter; when a change in load level from light load to heavy load and a change in material type are detected, the current PID parameter and the target PID parameter are weighted and fused, and the weighting coefficient increases from 0 to 1 according to a preset step value, with the switching completion time being 10 milliseconds to 200 milliseconds.

10. The adaptive load speed control system for an electric hammer according to claim 8, characterized in that, The inertial start protection module includes an overcurrent detection unit, a mode switching unit, and a dynamic torque limiting unit. The overcurrent detection unit compares the real-time current value with the hardware overcurrent threshold through a comparator. When the current exceeds the threshold, it directly outputs a hardware blocking signal to force the PWM output low in order to protect the power device. The mode switching unit automatically selects three pre-stored PID parameters to start operation based on the load level code output by the load status judgment terminal. The dynamic torque limiting unit calculates the maximum allowable output torque limit in real time based on the material type and load trend output by the load state judgment terminal. In concrete mode, the maximum allowable torque limit is 80% of the rated torque; in steel mode, the maximum allowable torque limit is 120% of the rated torque; and in wood mode, the maximum allowable torque limit is 100% of the rated torque.

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