Balancing mechanism for electric machine tool and electric machine tool

Abstract

The invention discloses a balancing mechanism for an electric machine tool, which is connected with an eccentric shaft (300) of the electric machine tool, and a tool head (200) of the electric machine tool rotates around a revolution axis (L1) of the eccentric shaft and rotates around a rotation axis (L2) when the tool head (200) works; the balance mechanism comprises a support (400) arranged on the eccentric shaft and a first balance assembly which comprises a first balance element (401) and a second balance element (402) which are located on the two sides of the eccentric shaft respectively. The first balance element is fixedly arranged relative to the eccentric shaft; the second balancing element can slide in the direction pointing to or deviating from the rotation axis. The sliding position of the second balance element is adjusted based on rotation of the eccentric shaft, so that the first balance assembly generates variable first balance force to balance friction force generated when the tool head works.

Description

Technical Field

[0001] The present invention relates to a balancing device, in particular to a balancing device for an electric machine tool. Background Art

[0002] Power tools, especially those with eccentric output shafts, often generate unbalanced forces during use. For example, the centrifugal force generated by the eccentric rotation of a polishing machine's tool head, as well as the friction generated when the tool head contacts the workpiece during grinding, can cause vibration and impact on the power tool, affecting the operator's experience and, in severe cases, shortening the tool's service life.

[0003] Based on this, current references tend to add a balancing block to the electric tool, hoping that the balancing block can generate an opposite force during the operation of the electric tool, thereby offsetting the unbalanced force generated during the operation of the electric tool, and thus reducing vibration and impact.

[0004] However, the unbalanced force generated by electric machine tools during operation is often variable rather than constant. For example, the tool head of a sanding machine has almost no friction when it is unloaded, but has greater friction when it is loaded. If a fixed balancing block is used, it cannot adapt to the friction during the no-load and load transition, and thus cannot achieve a good vibration reduction effect. Summary of the Invention

[0005] One of the objectives of the present invention is to provide a balancing mechanism for an electric machine tool, which can offset or reduce the unbalanced force generated by the electric machine tool during operation, thereby achieving a better balancing effect and further reducing vibration and impact on the electric machine tool.

[0006] To achieve the above objectives, the present invention provides a balancing mechanism for an electric machine tool, which is connected to an eccentric shaft of the electric machine tool. The eccentric shaft is used to connect to a tool head of the electric machine tool. The eccentric shaft has an orbital axis and a rotational axis offset from the orbital axis. When the tool head is in operation, it rotates about the orbital axis and about the rotational axis. The balancing mechanism includes:

[0007] a bracket, which is used to be arranged on the eccentric shaft;

[0008] a first balancing assembly comprising: a first balancing element and a second balancing element, respectively located on either side of the eccentric shaft; wherein the first balancing element is fixed relative to the eccentric shaft; and the second balancing element is slidably disposed on the bracket, and is capable of sliding in a direction toward or away from the rotation axis;

[0009] The second balancing element adjusts its sliding position based on the rotation and load state of the eccentric shaft, so that the first balancing assembly generates a variable first balancing force to balance the friction force generated by the tool head when it is working.

[0010] Another object of the present invention is to provide an electric machine tool that is subjected to balanced forces, has low vibration, and provides a good user experience when in use, including when unloaded and when loaded.

[0011] Based on this, the present invention further provides an electric machine tool, which includes the balancing mechanism as described above.

[0012] The balancing mechanism described in the present invention can effectively offset or reduce unbalanced forces generated during the operation of a power tool. In particular, it can generate a balancing force that varies according to the rotation of the eccentric shaft and the load state. This allows the friction generated by the tool head during workpiece handling under load to be offset or balanced. Furthermore, in the unloaded state (no friction, increased speed), the resultant force of the balancing assembly approaches zero, eliminating any additional unbalanced forces. Therefore, the balancing mechanism can adapt to both loaded and unloaded operating conditions, effectively reducing vibration throughout the power tool's operation and significantly improving user comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 An electric machine tool to which the present invention is applicable is schematically shown.

[0014] Figure 2 An eccentric shaft is shown.

[0015] Figure 3 A schematic three-dimensional structural diagram of a balancing mechanism for an electric machine tool according to one embodiment of the present invention is shown.

[0016] Figure 4 The balancing mechanism according to the present invention for an electric power tool is shown in one embodiment in the unloaded state of the tool head.

[0017] Figure 5 Schematic diagram showing the friction forces generated when the tool head is loaded.

[0018] Figure 6 The figure shows the stress state of the balancing mechanism for an electric machine tool according to the present invention in one embodiment when the tool head is loaded.

[0019] Figure 7 A partial view shows a spring element of a balancing mechanism for an electric machine tool according to the present invention in one embodiment.

[0020] Figure 8FIG1 schematically shows a structural diagram of a balancing mechanism for an electric machine tool according to another embodiment of the present invention.

[0021] Figure 9 A front structural schematic diagram of a balancing mechanism for an electric machine tool according to the present invention is shown in one embodiment.

[0022] Figure 10 A schematic side structural diagram of a balancing mechanism for an electric machine tool according to one embodiment of the present invention is shown.

[0023] Figure 11 The balancing force generated by the second balancing component of the balancing mechanism for an electric machine tool according to one embodiment of the present invention is schematically shown.

[0024] Figure 12 Another arrangement of the second balancing component of the balancing mechanism for an electric machine tool according to the present invention in one embodiment is schematically shown. DETAILED DESCRIPTION

[0025] The balancing mechanism for an electric tool and the electric tool according to the present invention will be further explained and illustrated below in conjunction with the accompanying drawings and specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0026] During use, electric machine tools, especially electric machine tools with eccentric output shafts, often generate unbalanced forces due to eccentricity.

[0027] Figure 1 An electric machine tool to which the present invention is applicable is schematically shown.

[0028] For example, Figure 1 The sanding machine 100 shown drives a tool head 200 connected thereto to rotate via the output shaft of the motor thereof, thereby sanding a workpiece.

[0029] Since the output shaft of the electric tool is an eccentric shaft, for example Figure 2 As described above, when the tool head 200 is started, it will revolve around the revolution axis L1 of the first shaft section 301 of the eccentric shaft 300, and simultaneously rotate around the rotation axis L2 of the second shaft section 302 of the eccentric shaft 300, thereby enabling the tool head 200 to grind the workpiece.

[0030] When the tool head 200 grinds the workpiece (not shown in the figure), unbalanced friction will be generated, and the friction will change with the change of the eccentric shaft load and the speed. This unbalanced force will bring vibration and impact to the power tool, thereby affecting the operator's experience, and in severe cases it will also affect the service life of the tool.

[0031] Based on this, the present invention provides, in one embodiment, a balancing mechanism for an electric machine tool, which is connected to an eccentric shaft 300 of the electric machine tool.

[0032] Figure 3 A schematic three-dimensional structural diagram of a balancing mechanism for an electric machine tool according to one embodiment of the present invention is shown.

[0033] like Figure 3 As shown, in some embodiments, the balancing mechanism may include a bracket (also referred to as a skeleton) 400, which is provided on the eccentric shaft 300 and is capable of rotating synchronously with the eccentric shaft 300. In some more specific embodiments, the bracket 400 can achieve synchronous rotation with the eccentric shaft by cooperating with the shaft hole of the eccentric shaft 300 through its center hole.

[0034] In addition, the balancing mechanism further includes a first balancing component for balancing the friction force. The first balancing component includes two balancing components located on both sides of the eccentric shaft 300 (for example, Figure 3 In the illustrated example, a first balancing element 401 and a second balancing element 402 are located on the left and right sides of the eccentric shaft 300. The first balancing element 401 is fixed relative to the eccentric shaft 300, and the second balancing element 402 is slidably mounted on the bracket 400. The second balancing element 402 can slide in a direction toward or away from the rotation axis L2 of the eccentric shaft 300.

[0035] The first balancing assembly of the present invention dynamically adjusts the magnitude of the resulting balancing force based on the eccentric shaft's rotational speed and load, thereby balancing and offsetting the varying frictional forces generated by the tool head during operation. It should be noted that the eccentric shaft's rotation, such as its rotational speed, is related to its load. When the eccentric shaft is heavily loaded, its rotational speed is low; when the eccentric shaft is lightly loaded, its rotational speed increases; and when the eccentric shaft is nearly unloaded, its rotational speed reaches its maximum.

[0036] like Figure 4 and Figure 6 As shown, in this embodiment, the second balancing element 402 can adjust its sliding position based on the rotational speed and load state of the eccentric shaft 300, so that the first balancing assembly generates a variable first balancing force to balance the variable friction force generated when the tool head is working.

[0037] in, Figure 4 The figure shows the state of the balancing mechanism when the tool head is unloaded. Figure 4 As shown, when the tool head is unloaded (ie, idling), it is not in contact with the workpiece being processed and no friction is generated.

[0038] In order to make the balancing mechanism of the present invention applicable to all working conditions of the electric tool, the present invention uses a first balancing element 401 and a second balancing element respectively provided on both sides of the eccentric shaft 300 to ensure that the first balancing force F1 generated by the first balancing assembly under no-load condition is 0, that is:

[0039] F1=F C -F D0

[0040] Among them, F C represents the balancing force generated by the first balancing element 401, F D0 It represents the balancing force generated by the second balancing element when the tool head is in the unloaded state.

[0041] In this case, the relationship between the first balancing element 401 and the second balancing element satisfies:

[0042]

[0043] Among them, m D represents the mass of the second balancing element 402, and r0 represents the center of mass O of the second balancing element 402 when the tool head is unloaded. D The distance from the rotation axis L2 to the rotation axis L2, ω0 represents the rotation speed of the second balancing element 402 when the tool head is in a no-load state, which is equal to the rotation speed of the tool head in a no-load state. Figure 4 It can be seen from the figure that at this time the second balancing element 402 slides to a position farther away from the eccentric shaft.

[0044] At this time, the mass m of the first balancing element C and the mass m of the second balancing element D satisfy:

[0045] m C ·r C =m D ·r0

[0046] where r C represents the distance from the center of mass of the first balancing element to the axis of rotation, and r0 represents the distance from the center of mass of the second balancing element to the axis of rotation when the tool head is in an idling state.

[0047] Of course, in other embodiments, the mass m of the first balancing element is C and the mass m of the second balancing element D The above formula may not be satisfied. In this case, the first balancing component can still achieve a balancing effect, but its balancing effect is inferior to that of the embodiment that satisfies the above formula.

[0048] When the tool head is rotated under load, e.g. Figure 5As shown, when it rotates in the counterclockwise direction at a speed of ω1, it will produce Figure 5 The friction force F is shown.

[0049] In this state, if Figure 6 As shown, the first balancing element 401 and the second balancing element respectively provided on both sides of the eccentric shaft 300 make the first balancing force F2 generated by the first balancing assembly under load equal to the friction force F, that is: (the sign of the first balancing force is F2 instead of F1)

[0050] F2=F=F C -F D1

[0051] Among them, F C represents the balancing force generated by the first balancing element 401, F D1 It represents the balancing force generated by the second balancing element when the tool head is loaded.

[0052] at this time:

[0053] F C >F D1 ;

[0054]

[0055] Among them, m D represents the mass of the second balancing element 402, and r1 represents the center of mass O of the second balancing element 402 under the tool head load state. D The distance from the rotation axis L2 to the rotation axis L2, ω1 represents the rotation speed of the second balancing element 402 under the tool head load state, that is, the rotation speed of the tool head under the load state, from Figure 6 It can be seen from the figure that at this time the second balancing element 402 slides to a position closer to the eccentric shaft.

[0056] In addition, in some preferred embodiments, the center of mass O of the second balancing element 402 D and the mass center O of the first balancing element 401 C The projection points of the rotation axis L2 on the same plane are collinearly arranged. Compared with the non-collinear arrangement, the collinear arrangement of the three points has better balancing and vibration reduction effects.

[0057] In some more specific embodiments, the sliding position of the second balancing element 402 can be adjusted by the elastic element 405, for example Figure 7 One end of the elastic element 405 is fixedly connected to the second balancing element 402, and the other end is fixedly connected to the eccentric shaft 300, so as to apply elastic force to the second balancing element 402 in the direction pointing to the rotation axis to pull it toward the rotation axis.

[0058] from Figure 4 and Figure 6 It can be seen that, in this embodiment, the stretching amount of the spring in the tool head unloaded state is greater than the stretching amount of the spring in the tool head loaded state.

[0059] Of course, in other more specific embodiments, the elastic element may also be a tension spring, a leaf spring, a butterfly spring, an elastic belt, or other elastic elements known to those skilled in the art.

[0060] The sliding position of the second balancing element 402 can be dynamically adapted to the rotational speed of the tool head by setting the mass of the second balancing element and the elastic coefficient k of the elastic element, as described above:

[0061]

[0062]

[0063] F C -F D0 =0

[0064] m C ·r C =m D ·r0

[0065]

[0066] Therefore: F D0 -F D1 =k·(r0-r1);

[0067] When ω0, ω1, and F are all known quantities measured or calibrated through experiments, in some embodiments, the mass m of the second balancing element can be designed by the following formula: D and / or the elastic modulus k of the elastic element:

[0068]

[0069]

[0070] Of course, in other embodiments, the mass m of the second balancing element is D Alternatively, the elastic coefficient k of the elastic element may not satisfy the above formula. In this case, the first balancing component can still achieve a balancing effect on the friction force, but its balancing effect is inferior to that of the implementation method that satisfies the above formula.

[0071] Furthermore, since the first balancing element 401 is fixed relative to the eccentric shaft 300, in some more specific embodiments, in order to make the structure of the balancing mechanism more concise, the gravity distribution of the eccentric shaft can be adjusted so that the first balancing element 401 is integrally formed on the eccentric shaft 300 (i.e., is provided as a part of the eccentric shaft 300).

[0072] In some other embodiments, the first balancing element 401 may also serve as a balancing weight independent of the eccentric shaft and be directly fixedly connected to the eccentric shaft.

[0073] In some other embodiments, the first balancing element 401 can also be fixedly mounted on any component fixedly connected to the eccentric shaft, for example, the first balancing element 401 can also be fixedly mounted on the bracket 400. In order to make the structure of the balancing mechanism more concise, the gravity distribution of the bracket 400 can also be adjusted so that the first balancing element 401 is integrally formed on the bracket 400, for example Figure 3 shown.

[0074] Of course, in some other more specific implementations, the first balancing element 401 may also be configured as a balancing block independent of the bracket 400 , and then the first balancing element may be fixedly connected to the bracket 400 using a connector.

[0075] As the second balancing element 402 needs to slide relative to the bracket 400 , it is configured as a balancing weight independent of the bracket 400 .

[0076] In some more specific embodiments, Figure 7 As shown, the second balancing element 402 can slide along the slide bar 406 fixedly connected to the bracket 400. In addition, when the elastic element 405 is a coil spring, the coil spring can also be sleeved on the slide bar 406, so that the slide bar 406 can provide it with certain support.

[0077] In some more specific embodiments, Figure 7 As shown, a limiting element 407 may be further provided at the free end (or referred to as the “end”) of the sliding rod 406 , and by providing the limiting element 407 , r0 may be adjusted and set as required.

[0078] Figure 8 FIG1 schematically shows a structural diagram of a balancing mechanism for an electric machine tool according to another embodiment of the present invention.

[0079] like Figure 8 As shown, in some other embodiments, the second balancing element 402 can be disposed in a housing 408 fixedly connected to the bracket, and a sliding groove can be provided on the bottom surface of the inner wall of the housing for the second balancing element to slide in a direction toward or away from the rotation axis. Figure 4 and Figure 6 The embodiment shown differs in that Figure 8 In the embodiment shown, the elastic element 405 is connected between the second balancing element 402 and the housing 408. When the tool head starts working, the elastic element 405 presses the second balancing element 402 toward the rotation axis instead of Figure 4 and Figure 6 The elastic element 405 in the embodiment shown pulls the second balancing element 402 towards the axis of rotation. Figure 8 In the embodiment shown, the length of the spring in the unloaded state of the tool head is shorter than the length of the spring in the loaded state of the tool head.

[0080] In some embodiments, power tools, such as grinding machines, can generate unbalanced centrifugal forces during operation. To balance this unbalanced centrifugal force, in some embodiments of the present invention, the balancing mechanism may further include a second balancing component that generates a second balancing force to counterbalance the centrifugal force generated by the rotation of the tool head. Similar to the first balancing component, the second balancing component is fixed relative to the eccentric shaft 300.

[0081] Figure 9 A front structural schematic diagram of a balancing mechanism for an electric machine tool according to the present invention is shown in one embodiment.

[0082] Figure 10 A schematic side view of the structure of a balancing mechanism for an electric machine tool according to the present invention in one embodiment is shown.

[0083] like Figure 9 and Figure 10 As shown, in this specific embodiment, the second balancing assembly may include a third balancing element 403 and a fourth balancing element 404 respectively provided on both sides (e.g., upper and lower sides) of the eccentric shaft 300, both of which are fixed on the bracket 400, and as shown in FIG. Figure 10 As shown, the third balancing element 403 and the fourth balancing element 404 are also respectively provided on two opposite axial end surfaces of the bracket 400 .

[0084] Figure 11 The balancing force generated by the second balancing component of the balancing mechanism for an electric machine tool according to one embodiment of the present invention is schematically shown.

[0085] like Figure 11 As shown, the tool head 200 of the electric tool generates a centrifugal force F during operation. L , which may cause the power tool to operate unstably. Therefore, in one embodiment of the present invention, a third balancing element 403 is provided to generate a balancing force F during the operation of the tool head. AThe fourth balancing element 404 disposed on the opposite side of the third balancing element 403 can generate a balancing force F during the operation of the tool head. A The opposite balancing force F B .

[0086] Therefore, by setting the mass and the position of the third balancing element 403 and the fourth balancing element 404, the resultant force F generated by the second balancing assembly is A -F B =F L , the centrifugal force can be balanced and offset.

[0087] In some more specific embodiments, the third balancing element 403 and / or the fourth balancing element 404 may be configured as balancing blocks independent of the bracket 400 and fixedly connected to the bracket 400 via fasteners, such as screws.

[0088] In other more specific embodiments, a separate second balancing assembly may not be provided, but instead the weight of the bracket may be distributed, for example, by trimming, partially thinning, partially thickening, or partially adding weight, so that the centrifugal force generated by the tool head is directly balanced by the bracket. In this case, the second balancing assembly may be integrally formed with the bracket 400.

[0089] In another case, the bracket 400 may be configured for weight distribution so that the bracket 400 can simultaneously realize the functions of the first balancing element 401 and the second balancing component.

[0090] Of course, in other embodiments, the second balancing assembly may also be configured to be connected to the eccentric shaft 300. In more specific embodiments, the second balancing assembly may be configured as a balancing weight independent of the eccentric shaft 300, fixedly connected to the eccentric shaft 300. In still other more specific embodiments, a separate second balancing assembly may not be provided, and instead the eccentric shaft may be weight-distributed, for example by trimming, locally thinning, locally thickening, or locally weighting, so that the centrifugal force generated by the tool head is directly balanced by the eccentric shaft. In this case, the second balancing assembly may also be integrally formed on the eccentric shaft 300.

[0091] In another case, the eccentric shaft 300 may be configured for weight distribution so that the eccentric shaft can simultaneously realize the functions of the first balancing element 401 and the second balancing component.

[0092] In addition, in some specific embodiments, the line connecting the mass centers of the third balancing element 403 and the fourth balancing element 404 can be as follows: Figure 9 The lines shown are completely coincident with the vertical direction.

[0093] In some other specific embodiments, the line connecting the mass centers of the third balancing element 403 and the fourth balancing element 404 can be as follows: Figure 12 As shown, when deflected by a certain angle relative to the vertical direction, in this case, the third balancing element and the second balancing element can play a part of the role of the first balancing element to balance the friction generated when the tool head is working.

[0094] Another embodiment of the present invention further provides an electric machine tool, which includes the balancing mechanism as described above.

[0095] The output shaft of the power tool is an eccentric shaft, which generates friction and, in some cases, centrifugal force when the tool head contacts the workpiece. In more specific embodiments, the power tool may be a grinding machine. However, it should be noted that the balancing mechanism can be installed in various power tools, including but not limited to grinding machines.

[0096] It should be noted that the terms "up", "down", "left" and "right" described in this article are for ease of understanding and are based on Figures 1 to 12 The present invention is not limited to the exemplary description of the configuration and direction of the present invention.

[0097] It should be noted that the prior art within the scope of protection of the present invention is not limited to the embodiments given in this application document. All prior art that does not contradict the solutions of the present invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of the present invention.

[0098] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0099] It should also be noted that the above-listed embodiments are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above-listed embodiments. Similar variations or modifications that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A balancing mechanism for an electric machine tool, connected to an eccentric shaft (300) of the electric machine tool, wherein the eccentric shaft is used to connect to a tool head (200) of the electric machine tool, wherein the eccentric shaft has an orbital axis (L1) and an autorotation axis (L2) deviating from the orbital axis, wherein the tool head rotates around the orbital axis and around the autorotation axis during operation; wherein: The balancing mechanism comprises: a bracket (400) configured to be disposed on the eccentric shaft (300); A first balancing assembly, comprising: a first balancing element (401) and a second balancing element (402) respectively located on both sides of the eccentric shaft; wherein the first balancing element is fixedly arranged relative to the eccentric shaft (300); and the second balancing element is slidably arranged on the bracket (400), and the second balancing element is capable of sliding in a direction toward or away from the rotation axis; The second balancing element adjusts its sliding position based on the rotation of the eccentric shaft, so that the first balancing assembly generates a variable first balancing force for balancing the friction force generated by the tool head when it is working.

2. The balancing mechanism according to claim 1, wherein: Also includes: A second balancing component is fixedly arranged relative to the eccentric shaft (300), and the second balancing component is configured to generate a second balancing force as the tool head rotates, so as to at least balance the centrifugal force and torque generated by the rotation of the tool head.

3. The balancing mechanism according to claim 2, wherein: The first balancing element (401) and / or the second balancing component are integrally formed on the bracket (400); or the first balancing element (401) and / or the second balancing component are integrally formed on the eccentric shaft (300).

4. The balancing mechanism according to claim 2, wherein: The second balancing assembly comprises a third balancing element (403) and a fourth balancing element (404) respectively arranged on both sides of the eccentric shaft (300); the third balancing element and the fourth balancing element are also respectively arranged on two opposite axial end faces of the bracket.

5. The balancing mechanism according to any one of claims 1 to 4, characterized in that: The center of mass of the second balancing element is collinear with the center of mass of the first balancing element and the projection point of the rotation axis.

6. The balancing mechanism according to any one of claims 1 to 4, characterized in that: The mass m of the first balancing element C and the mass m of the second balancing element D satisfy: m C ·r C =m D ·r0 where r C represents the distance from the center of mass of the first balancing element to the rotation axis, and r0 represents the distance from the center of mass of the second balancing element to the rotation axis when the tool head is in a no-load state.

7. The balancing mechanism according to any one of claims 1 to 4, characterized in that: The second compensating element is configured such that its mass m D satisfy: Among them, F represents the friction force generated by the tool head under load, r0 represents the distance from the center of mass of the second balancing element of the tool head to the rotation axis under no load, r1 represents the distance from the center of mass of the second balancing element of the tool head to the rotation axis under load, ω0 represents the rotation speed of the tool head under no load, and ω1 represents the rotation speed of the tool head under load.

8. The balancing mechanism according to any one of claims 1 to 4, characterized in that: The first balancing component further comprises an elastic element (405) connected to the second balancing element (402) to apply an elastic force to the second balancing element in a direction pointing to the rotation axis.

9. The balancing mechanism according to claim 8, wherein: The elastic element is constructed such that its elastic coefficient k satisfies: Wherein, F represents the friction force generated by the tool head under load, r0 represents the distance from the center of mass of the second balancing element of the tool head to the rotation axis under no load, and r1 represents the distance from the center of mass of the second balancing element of the tool head to the rotation axis under load.

10. The balancing mechanism according to any one of claims 1 to 4, characterized in that: A sliding rod (406) is fixedly connected to the bracket, and the second balancing element slides along the sliding rod in a direction pointing toward or away from the rotation axis.

11. The balancing mechanism according to claim 10, wherein: The free end of the slide rod is provided with a limiting element (407).

12. An electric machine tool, characterized in that: It comprises a balancing mechanism as claimed in any one of claims 1 to 11.

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