Method for controlling an electric motor using a trigger

Abstract

A method for controlling an electric motor (11) by means of a trigger (12a), characterized in that it comprises: - selecting a smoothing factor N based on a stroke variation quantity ΔL of the trigger (12a) during a preset time period; - calculating an output duty cycle DN using the formula DN = DN−1(N−1)+DRN; - driving the electric motor (11) by means of a control signal whose duty cycle is the output duty cycle DN, where DRum is an actual duty cycle corresponding to a stroke quantity of the trigger (12a) and DN−1 is the output duty cycle calculated for the last time.

Description

TECHNICAL AREA The present invention relates to a control method for an electric motor, in particular a method for controlling an electric motor by means of a trigger. STATE OF THE ART WO 2014 / 119203 A1 describes a housing for an electrically powered machine tool equipped with multiple battery packs. Each battery pack contains a battery. The housing of the electrically powered machine tool acquires discharge capacity information from each of the multiple battery packs, indicating the discharge capability of the battery installed within it. The housing of the electrically powered machine tool defines at least one control parameter for controlling an electrical discharge from a power source to a motor, based at least on the discharge capacity information of the battery with the lowest discharge capability among those acquired. Power tools, such as electric drills and electric screwdrivers, typically use a trigger switch to control the electric motor. The trigger switch controls the switching on and off of the circuit and the current level based on the trigger's stroke size. In general, in power tools, the trigger switch is connected in series in the power supply circuit of the electric motor, so that a user can control the rotation of the electric motor by operating the trigger switch. However, in actual use, the user typically tends to pull the trigger switch quickly, causing a larger current to flow through the electric motor in a short period. This can result in an electric shock to both the electric motor and other electronic components in the power tool, easily shortening the lifespan of the electric motor and causing heat damage to the electronic components. Furthermore, excessive current fluctuations can lead to instability in the battery voltage, potentially causing misjudgment of the current and malfunctioning of the protection circuitry. CONTENT OF THE PRESENT INVENTION The invention is defined by the attached claims. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows a structural block diagram of a preferred embodiment of a power tool for which a control method of the present invention is suitable. Fig. 2 shows a logic block diagram of a preferred embodiment of a control method of the present invention. Fig. 3 shows a logic block diagram of another preferred embodiment of a control method of the present invention. DETAILED DESCRIPTION Studies have found that when operating a power tool where a trigger switch serves as the control element, the user usually tends to pull the trigger switch quickly. Detection and testing revealed that, with existing power tools, this user habit can lead to the generation of a larger current in a short period. Each instance of a large current being generated causes a shock to the electric motor and other electronic components within the power tool, easily shortening the motor's lifespan and causing heat damage to the electronic components. Furthermore, excessive current fluctuations can lead to instability in the battery voltage, potentially causing misjudgment of the current output and malfunctioning of the protective circuitry. To overcome the shortcomings of the prior art, a method for controlling an electric motor using a trigger is provided below, which mainly comprises the following: - Selecting a smoothing factor N based on a stroke variation ΔL of the trigger switch during a unit time; - Calculating an output duty cycle DN using a formula; - Driving the electric motor using a control signal where the duty cycle is the output duty cycle DN, where DRum is the actual duty cycle corresponding to the stroke of the trigger switch and DN-1 is the last calculated output duty cycle. The actual duty cycle DR is a duty cycle of the trigger switch that corresponds to a current stroke size and is normally output when its stroke size changes smoothly. The above method can be implemented using an electric tool 100 as shown in Fig. 1. The power tool 100 according to Fig. 1 is a preferred structure that can implement the method of the present invention for controlling the electric motor 11 by means of the trigger 12a, comprising: a power source 13, an electric motor 11, a control switch 15, an MCU chip 14 and a trigger switch 12. The power source 13, the electric motor 11, and the control switch 15 form a main loop, with the control switch 15 responsible for controlling the switching on and off of the main loop. The MCU chip 14 serves to transmit a control signal with a specific duty cycle to the control switch 15 in order to control the switch 15 for switching the main loop on and off at the corresponding duty cycle. The trigger switch 12 is for actuation by the user and includes a movable trigger 12a. The trigger switch 12 can provide feedback on the stroke variation of the trigger 12a to the MCU chip 14 via an electrical signal. Corresponding duty cycle data is stored in the MCU chip 14 to match the stroke variation of the trigger switch 12. See Fig. 2, a further method for controlling the electric motor 11 by means of the trigger 12a is described below, comprising the following: (101) detecting a stroke position L1 of the trigger switch 12; (102) waiting for the preset time; (103) detecting a stroke position L2 of the trigger switch 12; (104) calculating a stroke variation ΔL = L2 - L1 of the trigger switch 12; (105) assessing whether the stroke variation ΔL of the trigger switch 12 is greater than 0; if it is greater than 0, step (6) is executed; If it is lower than 0, step (109) is executed; (106) Selecting a smoothing factor N based on a stroke variation quantity ΔL of the trigger switch 12; (107) Calculating an output duty cycle DN of the control signal to drive the drive motor 11 using the following formula DN; (108) Driving the drive motor 11 using a control signal where the duty cycle is DN, then returning to step (101);(109) Drive the drive motor 11 by means of a control signal where the duty cycle is DR, then return to step (101); DRum is the actual duty cycle corresponding to the stroke size of the trigger switch, and DN-1um is the output duty cycle calculated for the last time. Referring to the power tool 100 according to Fig. 1, the MCU chip 14 is responsible for detection and control, wherein the MCU chip 14 can detect the stroke size of the trigger switch 12 via a voltage signal of the trigger switch 12 and a corresponding relationship of the stroke size. It should be noted that DN-1 can be set to 0 during initial control. Preferably, several stroke variation ranges are provided, each corresponding to a different smoothing factor, and the stroke variation of the trigger switch 12 is detected at each of the predefined time intervals, and a corresponding smoothing factor is selected based on the stroke variation range in which the stroke variation lies. The advantage of this is to reduce the amount of data required for the smoothing factor. Preferably, a higher stroke variation corresponds to a higher smoothing factor. The advantage here is that a higher smoothing factor is more conducive to reducing the output duty cycle DN when the stroke of the trigger switch 12 increases rapidly. Preferably, the smoothing factor has a minimum value of 1. This makes it possible for the output duty cycle DN to be equal to the actual duty cycle DRist and for the electric motor 11 to perform an output based on the actual stroke position of the trigger switch 12, if the stroke variation of the trigger switch 12 is within a permissible range. The following describes another method for controlling the electric motor 11 using the trigger 12a, which differs from the method above and comprises the following: - Detecting an initial duty cycle D1 corresponding to a first stroke position of the trigger 12a when a preset time period begins; - Detecting an end duty cycle D2 corresponding to a second stroke position of the trigger 12a when the preset time period has ended; - Selecting a corresponding smoothing factor N based on the duty cycle difference value ΔD; - Calculating an output duty cycle D using a formula; - Driving the electric motor 11 using a control signal where the duty cycle is the output duty cycle D. See Fig. 3, a further method for controlling the electric motor 11 by means of the trigger 12a is described below, comprising the following: (201) detecting an initial duty cycle D1 corresponding to the stroke position of the trigger 12a; (202) waiting for the preset time; (203) detecting an end duty cycle D2 corresponding to the stroke position of the trigger 12a; (204) calculating a duty cycle difference value ΔD = D2 - D1; (205) assessing whether the duty cycle difference value ΔD is greater than 0; if it is greater than 0, step (206) is executed; If it is lower than 0, step (209) is executed; (206) Selecting a suitable smoothing factor N based on the duty cycle difference value ΔD; (207) Calculating an output duty cycle D using a formula; (208) Driving the drive motor 11 by means of a control signal where the duty cycle is D, then returning to step (201);(209) Drive the drive motor 11 by means of a control signal where the duty cycle is D2, then return to step (201); In this method, it can still be implemented using the power tool 100 according to Fig. 1, whereby the MCU chip 14 is responsible for detection and control, whereby the MCU chip 14 can detect the stroke size of the trigger switch 12 via a voltage signal of the trigger switch 12 and a corresponding relationship of the stroke size. Preferably, several duty cycle difference value ranges are provided, each corresponding to a different smoothing factor, and the duty cycle difference value ΔD is calculated for each of the specified preset time durations, and a corresponding smoothing factor is selected based on the duty cycle difference value range in which the duty cycle difference value lies. Furthermore, a higher duty cycle difference value corresponds to a higher smoothing factor, with the smoothing factor having a minimum value of 1. In summary, the method of the present invention for controlling the electric motor 11 using the trigger 12a mainly comprises the following steps: selecting a smoothing factor based on a stroke variation of the trigger switch 12 within a preset time period or a variation of a parameter corresponding to the stroke variation; calculating an output duty cycle such that an increase in the duty cycle before the preset time corresponding to the output duty cycle is inversely proportional to the smoothing factor; driving the drive motor 11 by means of a control signal, where the duty cycle is the output duty cycle. The basic principles, main features, and advantages of the present invention are shown and explained above. This is not intended to limit the scope of protection defined by the accompanying claims.

Claims

Method for controlling an electric motor (11) by means of a trigger (12a), characterized in that it comprises: - selecting a smoothing factor N based on a stroke variation quantity ΔL of the trigger (12a) during a preset time period; - calculating an output duty cycle DN using the formula DN = DN − 1 ( N − 1 ) + DRN ; - Driving the electric motor (11) by means of a control signal whose duty cycle is the output duty cycle D N is, whereby D R to achieve an actual duty cycle corresponding to a stroke size of the trigger (12a) and at D N-1 This refers to the last calculated initial duty cycle. Method for controlling an electric motor (11) according to claim 1, characterized in that several stroke variation size ranges are provided, wherein each of the stroke variation size ranges corresponds to a different smoothing factor, and wherein a corresponding smoothing factor N is selected on the basis of the stroke variation size range in which the stroke variation size ΔL of the trigger (12a) is located. Method for controlling an electric motor (11) according to claim 1, characterized in that a higher stroke variation quantity ΔL corresponds to a higher smoothing factor N. Method for controlling an electric motor (11) according to claim 1, characterized in that the smoothing factor has a minimum value of 1. A method for controlling an electric motor (11) by means of a trigger (12a), characterized in that it comprises: - detecting a stroke position L1 of the trigger (12a) when a preset time period begins; - detecting a stroke position L2 of the trigger (12a) when the preset time period has ended; - calculating a stroke variation ΔL = L2 - L1 of the trigger (12a); - assessing whether the stroke variation ΔL of the trigger (12a) is greater than 0; - selecting a smoothing factor N based on the stroke variation ΔL of the trigger (12a) if the stroke variation ΔL is greater than 0; - calculating an output duty cycle DN of the control signal used to drive the electric motor (11) using a formula DN = DN − 1 ( N − 1 ) + DN. D N where D R to achieve an actual duty cycle corresponding to a stroke size of the trigger (12a) and at D N-1 this concerns the last calculated initial duty cycle; - Driving the electric motor (11) by means of the control signal, whose duty cycle is the output duty cycle D N is. A method for controlling an electric motor (11) by means of a trigger (12a), characterized in that it comprises: - detecting an initial duty cycle D1 corresponding to a first stroke position of the trigger (12a) when a preset time period begins; - detecting an end duty cycle D2 corresponding to a second stroke position of the trigger (12a) when the preset time period has ended; - calculating a duty cycle difference value ΔD according to ΔD = D2 - D1; - assessing whether the duty cycle difference value ΔD is greater than 0; - selecting a corresponding smoothing factor N based on the duty cycle difference value ΔD if the duty cycle difference value ΔD is greater than 0; - calculating an output duty cycle D using a formula D = D1 + ΔDN; - Driving the electric motor (11) by means of a control signal, where the duty cycle is the output duty cycle D. Method for controlling an electric motor (11) according to claim 6, characterized in that several duty cycle difference value ranges are provided, wherein each of the duty cycle difference value ranges corresponds to a different smoothing factor, and wherein a corresponding smoothing factor is selected on the basis of the duty cycle difference value range in which the duty cycle difference value ΔD is located. Method for controlling an electric motor (11) according to claim 6, characterized in that a higher duty cycle difference value corresponds to a higher smoothing factor. Method for controlling an electric motor (11) according to claim 6, characterized in that the smoothing factor has a minimum value of 1.

Images