Electric tool and cam shaft for electric tool

Abstract

A power tool and a camshaft for a power tool. The power tool includes a housing, a motor supported within the housing and including an output shaft, a transmission assembly, and an impact mechanism. The motor is configured to rotationally drive the output shaft. The transmission assembly is configured to be rotationally driven by the output shaft. The impact mechanism includes a camshaft, a hammer, and an anvil configured to be rotationally driven by the transmission assembly. The camshaft has a groove, and at least a portion of the groove is defined by an equation selected from the group consisting of a trigonometric equation and a high-order differential equation. The hammer is coupled to the camshaft by a cam ball received in the slot. The anvil is configured to receive intermittent rotational impacts from the hammer.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 620,557, filed January 12, 2024, the entirety of which is incorporated by reference herein. TECHNICAL FIELD

[0003] The present utility relates to power tools having an impact mechanism, and more particularly to power tools having a rotary impact mechanism (“rotary impact tools”), such as impact drivers, impact wrenches, and the like. BACKGROUND

[0004] Rotary impact tools generally include a hammer coupled to a camshaft such that the hammer can reciprocate along the camshaft, store energy in a spring, and also rotate relative to the camshaft to impart periodic rotary impacts to an anvil. SUMMARY

[0005] The reciprocating motion of the hammer along the camshaft produces axial vibrations, which can cause user discomfort and fatigue. Accordingly, the present utility can provide, among other things, a camshaft configured to provide a rotary impact type power tool having a smoother operation and less vibration.

[0006] For example, in one aspect, the technology described in the present utility relates to a power tool comprising: a housing; a motor supported within the housing and including an output shaft, the motor configured to rotationally drive the output shaft; a transmission assembly configured to be rotationally driven by the output shaft; and an impact mechanism including a camshaft, a hammer, and an anvil. The camshaft is configured to be rotationally driven by the transmission assembly. The camshaft has a slot, and at least a portion of the slot is defined by an equation selected from the group consisting of a trigonometric equation and a higher-order differential equation. The hammer is coupled to the camshaft by a cam ball received in the slot. The anvil is configured to receive intermittent rotary impacts from the hammer.

[0007] In some aspects, a portion of the slot is defined by a cosine equation. In other aspects, the hammer is configured to rotationally impact the anvil when the cam ball is in a portion of the slot defined by the cosine equation.

[0008] In some aspects, a portion of the slot is a first slot portion, and the slot includes a second slot portion defined by a linear equation. In other aspects, the first slot portion and the second slot portion intersect at a transition point, and the first slot portion and the second slot portion are continuous and tangent at the transition point. In other aspects, the slot includes a third slot portion defined by an equation of a circle. In other aspects, the slot includes two second slot portions and the first slot portion extends between the two second slot portions, and the slot includes two third slot portions and each third slot portion extends from a corresponding one of the second slot portions.

[0009] In some aspects, the entire slot is defined by an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation.

[0010] In some aspects, the camshaft extends along an axis, and the slot is mirrored on either side of the axis.

[0011] In another aspect, the technology described in this document relates to a camshaft for an impact mechanism, the camshaft comprising a slot configured to receive a cam ball, the slot comprising a first portion defined by a first equation, a second portion defined by a second equation, and a third portion defined by a third equation, wherein at least one of the first equation, the second equation, and the third equation is an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation.

[0012] In some aspects, only one of the first equation, the second equation, and the third equation is an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation.

[0013] In some aspects, the first equation is a cosine equation having an amplitude, the amplitude of the cosine equation defining a forward-most point of the slot, the second slot portion extends from an end of the first slot portion opposite the amplitude, and the third slot portion extends from an end of the second slot portion opposite the first slot portion. In other aspects, the camshaft extends along an axis, and the slot is mirrored on either side of the axis, such that the slot comprises two second slot portions and two third slot portions. In other aspects, the second equation is a linear equation, and the third equation is an equation of a circle.

[0014] In some aspects, each of the first equation, the second equation, and the third equation is a different type of equation.

[0015] In yet another aspect, the technology described in this document relates to a power tool, the power tool comprising a housing, a motor supported within the housing and comprising an output shaft, a transmission assembly, and an impact mechanism. The motor is configured to rotationally drive the output shaft. The transmission assembly is configured to be rotationally driven by the output shaft. The impact mechanism comprises a camshaft, a hammer, and an anvil. The camshaft is configured to be rotationally driven by the transmission assembly. The camshaft has a slot having a first slot portion and a second slot portion that intersect at a transition point. The first slot portion and the second slot portion are continuous and tangent at the transition point. The hammer is coupled to the camshaft by a cam ball received in the slot. The anvil is configured to receive intermittent rotational impacts from the hammer.

[0016] In some aspects, the first slot portion is defined by a first equation and the second slot portion is defined by a second equation, and wherein the first equation and the second equation are different. In other aspects, one of the first equation and the second equation is an equation selected from the group of equations consisting of: a triangular equation and a higher order differential equation, and the other of the first equation and the second equation is a linear equation.

[0017] In some aspects, the transition point is a first transition point, and the slot further comprises a third slot portion, such that the second slot portion and the third slot portion intersect at a second transition point, and the second slot portion and the third slot portion are continuous and tangent at the second transition point. In other aspects, each of the first slot portion, the second slot portion, and the third slot portion is defined by a different equation than the other of the first slot portion, the second slot portion, and the third slot portion. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a perspective view of an impact wrench according to an embodiment of the present application.

[0019] Figure 2 is Figure 1 a cross-sectional view of the impact wrench of

[0020] Figure 3 is Figure 1 a perspective view of a camshaft and hammer of the impact wrench of

[0021] Figure 4 is Figure 3 a plan view of the camshaft of

[0022] Figure 5 is Figure 4 a schematic view of a cam slot of the camshaft of

[0023] FIG. 6 shows a plot of position, velocity, and acceleration curves for a camshaft having a prior art cam profile.

[0024] Figure 7 shows a plot of position, velocity, and acceleration curves for a camshaft having a Figure 4

[0025] Figure 8A is a plan view of a camshaft according to another embodiment of the present application.

[0026] Figure 8B is Figure 8A another plan view of the camshaft of

[0027] Figure 8C is Figure 8A a perspective view of the camshaft of

[0028] Figure 9 ​A graph showing position, velocity, and acceleration profiles of a camshaft according to another embodiment of the present disclosure is shown.

[0029] Before any embodiments of the present application are explained in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The application is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and not of limitation. DETAILED DESCRIPTION

[0030] Figure 1 and Figure 2 An electric power tool in the form of an impact wrench 10 is shown. The impact wrench 10 includes a housing 14 having a drive unit housing portion 18, a handle housing portion 22 extending downwardly from the drive unit housing portion 18, an intermediate case 26, and an impact case or front housing portion 30 coupled to and extending forwardly from the drive unit housing portion 18. In the illustrated embodiment, the drive unit housing portion 18 and the handle housing portion 22 are defined by cooperating first and second clamshell halves or housing portions. The drive unit housing portion 18 houses a drive unit 34 configured to generate or produce a torque output. The handle housing portion 22 defines a grip portion configured to be grasped by a user for operating the impact wrench 10. The intermediate case 26 houses a transmission assembly 38 configured to receive torque from the drive unit 34. The drive unit 34 and the transmission assembly 38 form a drive assembly. The front housing portion 30 houses an impact mechanism 42 configured to receive torque from the transmission assembly 38 and provide or deliver torque at an output end 46 of the impact wrench 10.

[0031] With continued reference to Figure 1 and Figure 2The drive unit 34 includes a motor 50, an output shaft 54 configured to be driven by the motor 50 to provide a torque output, a printed circuit board assembly (“PCBA”) 58 for controlling operation of the motor 50, and a fan 62 mounted to the output shaft 54. The motor 50 is a brushless direct current (“BLDC”) motor. Thus, the motor 50 can include a stator and a rotor. The output shaft 54 defines a motor axis Al. The output shaft 54 is supported by a rear bearing 66 and a front bearing 70. The rear bearing 66 and the front bearing 70 are each supported by the drive unit housing portion 18. In the illustrated implementation, the PCBA 58 is positioned between the motor 50 and the front bearing 70. In other implementations, the PCBA 58 can be positioned elsewhere. The fan 62 is mounted to the output shaft 54 at a location between the motor 50 and the rear bearing 66. Thus, the motor 50 is configured to drive rotation of the fan 62. As the fan 62 rotates, the fan 62 can cause a flow of cooling air to flow through the motor 50 to cool the motor 50 and the PCBA 58.

[0032] The handle housing portion 22 defines a grip and a battery receptacle 74 that receives a battery 78 configured to power the motor 50. The battery 78 can be a power tool battery pack (e.g., an 18-volt rechargeable battery or an M18 REDLITHIUM battery pack sold by Milwaukee Electric Tool Corporation) that is commonly used to power power tools such as electric drills. The battery 78 can include a lithium-ion (Li-ion) battery. In alternative implementations, the battery 78 can have a different chemistry (e.g., nickel-cadmium (NiCa or NiCad), nickel-hydrogen, etc.). In the illustrated implementation, the battery 78 can be a 4-volt battery pack, a 28-volt battery pack, a 40-volt battery pack, or any other voltage battery pack suitable for powering the impact wrench 10. The grip supports a switch 82 (e.g., a trigger switch) that is actuatable to electrically connect the motor 50 and the battery 78 to provide DC power to the motor 50. Thus, a user can actuate the switch 82 to send a signal to the PCBA 58 to energize the motor 50 so that the drive unit 34 begins to generate torque.

[0033] As Figures 2-4As shown, the transmission assembly 38 includes a carrier 86, a plurality of planet gears 90, and a ring gear 94. The carrier 86 supports the plurality of planet gears 90. The carrier 86 can include a rear wall 86a, a front wall 86b, and a plurality of pins 98 extending between the rear wall 86a and the front wall 86b, such that each of the planet gears 90 is mounted or coupled to a corresponding one of the pins 98 between the rear wall 86a and the front wall 86b. Each planet gear 90 includes gear teeth that are in meshing engagement with the pinion gear 54a of the output shaft 54, such that rotation of the output shaft 54 drives movement and rotation of the planet gears 90. Each planet gear 90 is also in meshing engagement with ring gear teeth formed on an inner surface of the ring gear 94. In this way, the output shaft 54 is configured to drive rotation of the planet gears 90 about the ring gear 94, such that the planet gears 90 orbit about the pinion gear 54a of the output shaft 54. Due to the coupling between the planet gears 90 and the corresponding one of the pins 98, the planet gears 90 provide a constant rotational force or torque to the carrier 86.

[0034] With continued reference to Figures 2-4 The impact mechanism 42 is configured to convert the constant rotational force or torque provided by the transmission assembly 38 into intermittent application of an impact rotational force or torque at the output end 46 of the impact wrench 10 for application to the workpiece 102. The impact mechanism 42 includes a cam shaft 106, a hammer 110, an anvil 114, and a spring 118. The cam shaft 106 is integrally formed with the carrier 86 of the transmission assembly 38, such that the motor 50 can provide a constant rotational force or torque to the cam shaft 106 through meshing engagement between the output pinion gear 54a and the planet gears 90. The cam shaft 106 extends along a rotational axis A2. The rotational axis A2 can also be referred to as an output shaft. In the illustrated embodiment, the rotational axis A2 is coaxial with the motor axis Al. The cam shaft 106 includes at least one cam slot 122 defined therein that is configured to receive at least one cam ball 126. The cam ball 126 is positioned in driving engagement with the hammer 110, such that movement of the cam ball 126 within the cam slot 122 allows the hammer 110 to move in relative axial motion along the cam shaft 106. In particular, the hammer 110 is configured to move axially along the cam shaft 106 to intermittently apply an impact rotational force or rotational impact to the anvil 114. The spring 118 extends from the carrier 86 to the hammer 110 and biases the hammer 110 toward the anvil 114.

[0035] In the illustrated embodiment, with reference to Figure 4The cam groove 122 has a first groove portion 130, a second groove portion 134, and a third groove portion 138. The designations of first, second, and third are arbitrary, such that the groove portions 130, 134, 138 can be referred to in any other order. For example, the first groove portion 130 can be referred to as the third groove portion, and the third groove portion 138 can be referred to as the first groove portion. The first groove portion 130 defines a first end of the cam groove 122. When the cam ball 126 is positioned in the first portion 130 of the cam groove 122, the hammer 110 can be in a rearmost position along the cam shaft 106. The second groove portion 134 extends between the first portion 130 and the third groove portion 138. The third groove portion 138 defines a second end of the cam groove 122. When the cam ball 126 is positioned in the third groove portion, the hammer 110 is in a foremost position along the cam shaft 106, such that the hammer 110 can strike the anvil 114. In the illustrated embodiment, the cam groove 122 is mirrored along a circumference or outer surface of the cam shaft 106 on both sides of the output axis A2. As such, the cam groove 122 includes two first groove portions 130 and two second groove portions 134. The third groove portion 138 extends between and connects the two second groove portions 134, such that the cam ball 126 can sequentially travel from the first groove portion 130 and the second groove portion 134 on one side of the output axis A2, through the third groove portion 138, and along the second groove portion 134 and the first groove portion 130 on the opposite side of the output axis A2. In other words, each of the second groove portions 134 extends from an end of the third groove portion 138 opposite the output axis A2 (i.e., the amplitude or the foremost position of the third groove portion 138), and each of the first groove portions 130 extends from an end of a corresponding one of the second groove portions opposite the third groove portion 138.

[0036] The first groove portion 130 is defined by a first equation, the second groove portion 134 is defined by a second equation, and the third groove portion is defined by a third equation. In the illustrated embodiment, each of the first equation, the second equation, and the third equation is different from the others. In other words, the first groove portion 130, the second groove portion 134, and the third groove portion 138 are each defined by a different equation. In some embodiments, the first equation, the second equation, and the third equation can all be the same. In other embodiments, the groove can have only one portion defined by a single equation. As will be described in greater detail below, the third equation is an equation selected from the group consisting of: a trigonometric equation and a higher-order differential equation.

[0037] Referring to Figure 4 and Figure 5, each of the first and second slot portions 130, 134 will be described below only for one portion 130, 134 (i.e., the portion 130, 134 on one side of the output axis A2). It should be understood that the description of each of the first and second slot portions 130, 134 on one side of the output axis A2 applies equally to the corresponding portion 130, 134 on the opposite side of the output axis A2. In some embodiments, the portion 130, 134 on one side of the output axis A2 can differ from the corresponding portion 130, 134 on the opposite side of the output axis A2. In the illustrated embodiment, the first slot portion 130 is defined by a particular radius. In other words, the first slot portion 130 is defined by a portion of a circle having a radius. Thus, the first slot portion 130 follows the equation of a circle as follows:

[0038] r 2 = (x-A) 2 + (y-B) 2

[0039] In this equation, the variables A and B set the position of the center of the circle. For example, the variable A sets the x-coordinate on the x-y coordinate system, and the variable B sets the y-coordinate on the x-y coordinate system. Thus, the variables A and B can be adjusted to set the starting position of the first slot portion 130 (e.g., aligned with the second slot portion 134). The variable r is the radius of the circle. Thus, the variable r can be adjusted to set the curvature of the first slot portion 130 from the starting position (e.g., aligned with the second slot portion 134). In particular, the first and second slot portions 130, 134 intersect at a transition point, and the equation of the circle can be determined such that the first and second slot portions 130, 134 are continuous and tangent at the transition point. The transition point between the first and second slot portions 130, 134 can be referred to as the first or second transition point.

[0040] In the illustrated embodiment, the second slot portion 134 extends linearly between the first slot portion 130 and the third slot portion 138. In particular, the second slot portion 134 extends at an angle a Rl relative to a horizontal axis (e.g., the x-axis on the x-y coordinate system). Thus, the second slot portion 134 is defined by a linear slope-intercept form equation as follows:

[0041] y = Cx + D

[0042] In this equation, the variable C is the slope at which the second slot portion 134 extends. Thus, the variable C can be adjusted according to the desired value of the angle a Rl. The variable D sets the starting position of the second slot portion 134. Thus, the variable D can be adjusted according to the desired starting and ending positions of the second slot portion 134.

[0043] In the illustrated embodiment, the third slot portion 138 extends between the two second slot portions 134. Specifically, the third slot portion 138 curves between the two second slot portions 134 such that the third slot portion 138 is mirrored on either side of the output axis A2. More specifically, the third slot portion 138 curves from each of the second slot portions 134 toward the output axis A2 according to one of a set of equations that includes a trigonometric equation and a higher-order differential equation. In other words, the third slot portion 138 is defined by one of a set of equations that includes a trigonometric equation and a higher-order differential equation. The trigonometric equation can include one or more trigonometric ratios of an angle, such as sine, cosine, tangent, cotangent, secant, or cosecant. The higher-order differential equation can be, for example, a second-order differential equation, a third-order differential equation, and so on. In the illustrated embodiment, the trigonometric equation that defines the third slot portion 138 is a cosine equation such that the third slot portion 138 is a cosine curve, as follows:

[0044] Y = (-E)cos(F(x-G)) + H

[0045] In this equation for the cosine curve, the variable E defines an amplitude of the cosine curve. Thus, the variable E can be adjusted to set a height of curvature of the cosine curve, and thus a forward-most point of the slot 122. The variable F defines a period of the cosine curve. Thus, the variable F can be adjusted to set a length of curvature of the cosine curve. The variable G defines a phase shift of the cosine curve. Thus, the variable G can be adjusted to set an x-coordinate of the cosine curve on an x-y coordinate system. The variable H defines a vertical displacement of the cosine curve. Thus, the variable H can be adjusted to set a y-coordinate of the cosine curve on the x-y coordinate system.

[0046] The one equation can also be referred to as a first equation, and the set of equations can also be referred to as a first set of equations. As such, the second slot portion 134 extends between the first slot portion 130 and the third slot portion 138 according to another equation (e.g., a second equation) from a second set of equations that includes at least a linear or slope-intercept form equation. In other words, the second slot portion 134 is defined by the second equation from the second set of equations. The second set of equations can further include, for example, an equation for a circle. In some embodiments, the second set of equations does not include a trigonometric equation or a higher-order differential equation.

[0047] The third slot portion 138 provides a continuous and tangent transition between the second slot portion 134 and the third slot portion 138 that eliminates sudden jerks or accelerations of the hammer 110 during operation of the impact mechanism 42. For example, FIG. 6 is a graph 142 that illustrates a position profile 146, a velocity profile 150, and an acceleration profile 154 of a camshaft having a conventional cam slot, which is defined in part by a circular (radius) function and a linear equation. As shown in FIG. 6, a line A3 indicates the position of a transition point between the second slot portion and the third slot portion (e.g., where the second slot portion and the third slot portion intersect) of the conventional cam slot relative to the position, velocity, and acceleration profiles 146, 150, 154 of the cam follower traveling along the conventional cam slot. During operation of the camshaft having the conventional cam slot, when the cam follower reaches the transition point, the travel of the cam follower can be affected or interrupted by the sudden change in acceleration between the second slot portion and the third slot portion, which is represented as a step in the acceleration profile 154. This sudden change in acceleration, as shown by the line A3 in FIG. 6, causes a jerk in the cam follower, and thus a jerk in the hammer.

[0048] Figure 7 is a graph 158 that illustrates a position profile 162, a velocity profile 166, and an acceleration profile 170 of the camshaft 106 of the illustrated embodiment having the cam slot 122 Figure 4 . Referring to Figure 4 and Figure 7 , a line A4 Figure 7 indicates the position of a transition point between the second slot portion 134 and the third slot portion 138 (e.g., where the second slot portion 134 and the third slot portion 138 intersect) relative to the position, velocity, and acceleration profiles 162, 166, 170 of the cam follower 126 traveling along the cam slot 122. Due to the cosine curve geometry of the third slot portion 138, the cam slot 122 does not include a step in the acceleration profile 170 that would cause a jerky motion of the cam follower 126, as observed with the conventional cam slot described above in connection with FIG. 6. Accordingly, as the cam follower 126 travels from the third slot portion 138 to the second slot portion 134, the acceleration of the cam follower 126 can smoothly decrease to zero.

[0049] Referring to Figure 4 and Figure 5R1 that minimizes the vibration felt by the operator and the loss of efficiency from operation of the impact mechanism 42. Specifically, the variables C, D, E, F, G, H are determined such that the value of the slope-intercept form equation that defines the second slot portion 134 and the value of the cosine curve equation that defines the third slot portion 138 are equal at a transition point between the second slot portion 134 and the third slot portion 138 (i.e., the location along the cam slot 122 where the second slot portion 134 and the third slot portion 138 intersect). In other words, the variables C, D, E, F, G, H are determined such that the second slot portion 134 and the third slot portion 138 are continuous at the transition point. The variables C, D, E, F, G, H are additionally determined such that the slope (i.e., derivative) of the slope-intercept form equation that defines the second slot portion 134 and the slope (i.e., derivative) of the cosine curve equation that defines the third slot portion 138 are equal at the transition point. In other words, the variables C, D, E, F, G, H are determined such that the second slot portion 134 and the third slot portion 138 are tangent at the transition point. In this way, the orientation of the cam slot 122 is advantageously determined such that the cam ball 126 is able to smoothly travel from the second slot portion 134 to the third slot portion 138 (and vice versa) without the sudden jerk caused by an impact between the cam ball 126 and a step in the cam shaft 106. The transition point between the second slot portion 134 and the third slot portion 138 can be referred to as the first or second transition point.

[0050] To determine the variables C, D, E, F, G, H based on the desired alpha angle R1, the slope-intercept form equation and the cosine curve equation are first solved based on a hypothetical transition point having values a and b. The value a is the x-coordinate of the transition point on the x-y coordinate system. The value b is the y-coordinate of the transition point on the x-y coordinate system. The x-y coordinate system represents the location on the outer surface of the cam shaft 106 where the output shaft A2 provides the y-axis. Thus, the value a is equal to the value of the adjacent line in the triangle with respect to the alpha angle R1, and the value b is equal to the value of the opposite line in the same triangle with respect to the alpha angle R1. Thus, the alpha angle R1 and the transition point are related by the following equation.

[0051] tan(A1) =

[0052] From the variables E, F, G, H of the cosine curve equation, variable E representing the amplitude of the cosine curve is determined based on the value b. Specifically, variable E is directly set equal to the value b. Variable F representing the period of the cosine curve is determined based on the value a. Specifically, variable E is set equal to π / (2a). Variable G representing the phase shift (e.g., the displacement along the x-axis of the x-y coordinate system) of the cosine curve is set equal to zero, such that the third slot portion 138 is centered at the output shaft A2. In some embodiments, the phase shift can be set equal to a non-zero value, such that the third slot portion 138 is not centered at the output shaft A2. Variable H representing the vertical displacement of the cosine curve is determined based on the value a. Specifically, variable D is directly set equal to the value b. Thus, the cosine curve can be simplified to the following equation.

[0053] y1= -(b)(cos( x) + b)

[0054] Variable C, D of the slope-intercept equation can then be determined using the equation y1. Variable C representing the slope of the slope-intercept form equation is determined from the derivative of the equation y1. Specifically, since the second slot portion 134 and the third slot portion 138 are tangent at the hypothetical transition point, the slope of the slope-intercept form equation is set equal to directly equal to the derivative of the equation y1 at the hypothetical transition point. Thus, after taking the derivative of the equation y1 and solving for the derivative at the hypothetical transition point, it is found that variable C or the slope is (π b ) / (2 a ). Variable D representing the y-intercept of the slope-intercept form equation is determined from both the value a and the value b. Specifically, as described above, variable D is determined by plugging in the value a in x, the value b in y, and the derived value of variable C in slope. Thus, by solving the slope-intercept form equation for variable D with these substitutions, it is found that variable D is b - (πb) / (2). Thus, the slope-intercept form equation can be simplified to the following equation.

[0055] y2= (x) + (–b - )

[0056] Using the derived theoretical equations yi, y2, actual equations for the second slot portion 134 and the third slot portion 138 can be determined by inserting known or desired values (e.g., arguments) into the equations yi, y2. In the illustrated embodiment, the actual equations are determined by inserting a desired a-angle Ri that determines the actual slope into the derived equations yi, y2 and solving the equations for the values a and b of the transition point using a system of equations. In some embodiments, the actual equations can be determined by inserting a known or desired transition point into the derived angles yi, y2 and solving for the a-angle Ri. The system of equations can include the equation yi, the equation y2, the derivative of the equation yi, and the derivative of the equation y2, as well as other relationships described by the present disclosure. In this way, once the equations yi, y2 are solved for the desired a-angle Ri, the second slot portion 134 and the third slot portion 138 can be formed (e.g., manufactured) in the camshaft 106 based on the resulting actual equations.

[0057] Figures 8A-8C Another embodiment of a camshaft 206 for a power tool 10 is shown. Figure 1 The camshaft 206 can be substantially similar to the camshaft 106 of Figure 4 the present disclosure. As shown in Figures 8A-8C the camshaft 206 includes at least one cam slot 210 defined in the camshaft 206 that is configured to receive at least one cam ball 214. The cam ball 214 can be positioned in driving engagement with a hammer, such as the hammer 110 shown in Figure 3 In this way, movement of the cam ball 214 within the cam slot 210 allows for relative axial movement of the hammer along the camshaft 206. In particular, the hammer is configured to move axially along the camshaft 206 to intermittently apply an impact rotational force or rotational impact on an anvil, such as the anvil 114 shown in Figure 2

[0058] The cam slot 210 is defined by one equation from a system of equations including a trigonometric equation and a higher order differential equation. In particular, the cam slot 210 is uniformly formed according to one equation from a system of equations including a trigonometric equation and a higher order differential equation. In the illustrated embodiment, the cam slot 210 is uniformly formed according to an equation of a cosine curve, as described above in connection with the third slot portion 138 shown in Figure 4 In other words, Figures 8A-8C ​The cam groove 210 is entirely defined by the equation of a cosine curve. As such, due to the uniformity of the cam groove 210, the cam ball 214 is allowed to travel smoothly between the ends 210a, 210b of the cam groove 210. That is, the cam groove 210 does not include steps that would otherwise cause jerky motion of the cam ball 214 as it travels along the cam groove 210. In some embodiments, the cam groove 210 can be uniformly formed according to the equation of a sine curve. In other embodiments, the cam groove 210 can be uniformly formed according to the equation of a higher order differential equation.

[0059] Figure 9 is a graph 250 showing a position curve 254, a velocity curve 258, and an acceleration curve 262 of a camshaft according to another embodiment of the present application. The camshaft includes a cam groove that is uniformly formed according to a higher order differential equation. The higher order differential equation can be a second order, third order, fourth order, fifth order, or higher order differential equation. Specifically, the higher order differential equation can be manipulated such that the curvature of the position curve 254 mimics the curvature of a sine curve or a cosine curve. Accordingly, the graph 250 further includes a reference cosine curve 266 for the position curve 254. In the illustrated embodiment, the position curve follows the equation of a general linear differential equation as follows.

[0060] L(y) = p0(t) + p1(t)y + p2(t)y2+ p3(t)y3+ p4(t)y4+ p5(t)y5+... + pN(t)yN + p1(t) + p 1-n (t) + p n (t)(y)

[0061] The above equations can be modified as desired to extend in a manner generally similar to a trigonometric equation.

[0062] The various features and advantages of the present application are set forth in the appended claims.

Claims

1. A power tool characterized by comprising: Comprising: a housing; a motor supported within the housing and including an output shaft, the motor configured to rotationally drive the output shaft; a transmission assembly configured to be rotationally driven by the output shaft; and an impact mechanism including: a camshaft configured to be rotationally driven by the transmission assembly, the camshaft having a slot, at least a portion of the slot defined by an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation, a hammer coupled to the camshaft by a cam ball received in the slot, and an anvil configured to receive intermittent rotational impacts from the hammer. The portion of the slot is defined by a cosine equation.

2. The power tool of claim 1, wherein, The hammer is configured to rotationally impact the anvil when the cam ball is in the portion of the slot defined by the cosine equation.

3. The power tool of claim 2, wherein, The portion of the slot is a first slot portion, and wherein the slot includes a second slot portion defined by a linear equation.

4. The power tool of any one of claims 1-3, wherein, The first slot portion and the second slot portion intersect at a transition point, and wherein the first slot portion and the second slot portion are continuous and tangent at the transition point.

5. The power tool of claim 4, wherein, The slot includes a third slot portion defined by an equation of a circle.

6. The power tool of claim 4, wherein, The slot includes two second slot portions, and the first slot portion extends between the two second slot portions, and wherein the slot includes two third slot portions, and each of the third slot portions extends from a corresponding one of the second slot portions.

7. The power tool as described in claim 6, characterized in that, The entire slot is defined by an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation.

8. The power tool of claim 1, wherein, The camshaft extends along an axis, and wherein the slot is mirrored on either side of the axis.

9. The power tool of claim 1, wherein, The camshaft includes:

10. A camshaft for an electric power tool, characterized by, a slot configured to receive a cam ball, the slot including a first slot portion defined by a first equation, a second slot portion defined by a second equation, and a third slot portion defined by a third equation, wherein at least one of the first equation, the second equation, and the third equation is an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation. Only one of the first equation, the second equation, and the third equation is an equation selected from the group consisting of: a trigonometric equation and a higher order differential equation.

11. The camshaft of claim 10, wherein, The first equation is a cosine equation having an amplitude, wherein the amplitude of the cosine equation defines a forward-most point of the slot, wherein the second slot portion extends from an end of the first slot portion opposite the amplitude, and wherein the third slot portion extends from an end of the second slot portion opposite the first slot portion.

12. The camshaft of claim 10, wherein, The camshaft extends along an axis, and wherein the slot is mirrored on either side of the axis, such that the slot includes two second slot portions and two third slot portions.

13. The camshaft of claim 12, wherein, The second equation is a linear equation, and wherein the third equation is an equation of a circle.

14. A camshaft as claimed in claim 12 or 13, characterised in that, Each of the first equation, the second equation, and the third equation is a different type of equation.

15. The camshaft of any one of claims 10-13, wherein, Comprising:

16. A power tool characterized by comprising: a housing; a motor supported within the housing and including an output shaft, the motor configured to rotationally drive the output shaft; ​ a transmission assembly configured to be rotationally driven by the output shaft; and an impact mechanism comprising: a camshaft configured to be rotationally driven by the transmission assembly, the camshaft having a slot with a first slot portion and a second slot portion intersecting at a transition point, the first slot portion and the second slot portion being continuous and tangent at the transition point, a hammer coupled to the camshaft by a cam ball received in the slot, and an anvil configured to receive intermittent rotational impacts from the hammer.

17. The power tool of claim 16, wherein the first and second electrical conductors are electrically connected to the motor. the first slot portion is defined by a first equation and the second slot portion is defined by a second equation, and wherein the first equation and the second equation are different.

18. The power tool of claim 17, wherein, one of the first equation and the second equation is an equation selected from a group of equations consisting of: a trigonometric equation and a higher order differential equation, and wherein the other of the first equation and the second equation is a linear equation.

19. The power tool of any one of claims 16-18, wherein, the transition point is a first transition point, wherein the slot further comprises a third slot portion such that the second slot portion and the third slot portion intersect at a second transition point, and wherein the second slot portion and the third slot portion are continuous and tangent at the second transition point.

20. The power tool of claim 19, wherein, each of the first slot portion, the second slot portion, and the third slot portion is defined by a different equation than the other slot portions of the first slot portion, the second slot portion, and the third slot portion.

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