JPS5810471A - Motor tool with ground - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grounded power tool, and more particularly to a grounded power tool having a structure suitable for suppressing key noise.

Noise from power tools that are normally grounded is thought to be caused by rapid changes in the flow of solder caused by rectification that propagate to the wiring path, and the manner in which the noise is propagated can be seen between two power lines. It can be considered by replacing it with a multi-terminal network consisting of a ground wire and a ground wire, but the propagation from the power tool is
It can be divided into line-to-line noise that propagates between power lines (called symmetrical noise) and line-to-ground noise that propagates between the power line and the ground line (called asymmetrical noise). It is known that a repulsion suppression method can be devised independently for each.

The line-to-earth noise will be mainly explained below.

Suppression of noise from power tools that are normally grounded is
Usually, the circuit configuration is shown in FIG. 1 or 2. In Figures 1 and 2, 1d housing, 2d
Armature, 3, field winding, 4a.

4b is a noise preventer, the noise preventer -aAa in FIG. 1 is composed of capacitors C3 to C3, and the mfk device 4b in FIG. 2 is composed of a capacitor to C3 and a common mode choke coil L.

In Figures 1 and 2, the elements that are effective in suppressing line-to-line noise are the capacitor Cp (3 m) and the chill coil L; the capacitor C1 works effectively only to suppress line-to-line noise. The prevention effect of the noise preventers 4a and Ab shown in FIGS. 1 and 2 is usually expressed in terms of insertion attenuation, and a theoretical equivalent circuit that takes this into account is shown in FIG.

In FIG. 3, zM is the phase angle of the impedance between the electric wire and the ground viewed from the noise prevention device mounting position, and is simply referred to as the tt power tool impedance. ), 2. from the outlet
The high-frequency load impedance (hereinafter simply referred to as load impedance) is equivalent to the line-to-ground impedance of the distribution line, and ■ is the equivalent generated force. However, the power cord must be replaced with a lossless power line.

When the circuits in FIGS. 1 and 2 are replaced with the t-S value circuit shown in FIG. 3, the circuits become as shown in FIGS. 4 and 5, respectively.

In FIGS. 4 and 5, zl represents noise preventers 4a and 4b.
The capacitor C7, (corresponds to 33) is inserted between the power supply line and the ground line.
This is the impedance inserted into the power line circuit b, and corresponds to the chimique coil L. The insertion attenuation of Z1%Z2 is αa, respectively (tb, then da and db are expressed by the following formulas, ・・・－・・・＋2) Noise preventers shown in Figures 1 and 2, respectively This is equivalent to the prevention effect against line-to-ground noise of 4a and 4b.

Fig. 6 is a schematic structural diagram of the electric motor part of the conventional grounding tool (gb tool). In Fig. 6, 1 is the housing, 5 is the field core, 3 is the field winding, and 6 is the Armature core, 7
is an armature winding, and 8 is a rotating shaft.

Fig. 7 is a diagram showing the frequency characteristics of impedance phase angle and impedance absolute value, where asfL' is the power tool impedance, absolute directness, and phase angle of the conventional power tool shown in Fig. 6, and b is the International Hearing Impairment Special Standard. This is the actual value of the load impedance of the artificial power supply network recommended in the recommendation of the Committee (C Engineering 5pR). From this, it can be seen that the power tool impedance exhibits a capacitive-inductive impedance characteristic in the frequency range of 0.15 to 5 MHz, and has two inflection points, Fl and F20. Therefore, ZM/(Zv+Z
t,') becomes small near the frequency of the inflection point F1 and in the high frequency region, and the prevention effect α of the noise preventers 4a and 4b is
a1αb decreases.

On the other hand, in power tools, even in models that are normally used with grounding 17, capacitors C2 and C3 in Figures 1 and 2 are connected to 3.
000pP to 4700t+Fm or less. Therefore, (at 115~[L3MHz, lz, /z-1
is 1 [near t, z value realized? ” ! No.

In addition, in the case of the electric power tool used in the conventional grounding device 12, the power tool impedance ZM is not so large compared to the load impedance zL, and the inflection point F1 is in a relatively low frequency region. ~ [The noise preventer 4a or 4b has little prevention effect in the 18 MHz frequency region.

Therefore, the noise from the power tool has a frequency of LL15MH.
Normally, it is largest in the vicinity of z, and relatively small in higher frequency regions.
Propagation of large noise in the low frequency region to the power distribution line [2]
Isn't the present invention made in view of the above? The purpose of the present invention is to provide a grounded power tool capable of reducing line-to-earth noise in the frequency range of 0.15 MHz to 0.8 MHz.

A feature of the present invention is that an insulating layer is provided between at least one of the field core and the armature core of the fIL machine of the power tool and the casing to provide electrical insulation. be.

The present invention will be explained in detail below with reference to the embodiments shown in FIG. 8, 1Ω diagram, and FIG. 11, as well as FIGS. 3 and 9.

FIG. 8 is a schematic structural diagram showing an embodiment of the electric motor portion of the earthed power supply IIth of the present invention. The same parts as in FIG.

The difference between FIG. 8 and FIG. 6 is that an insulating layer 15 made of plastic or the like is provided between the armature core 6 and the rotating shaft 8. In addition, 9 is a commutator, 10 is a brush, 1
1 is a brush holder, 12 is a ball bearing, 13 is a fan, and 14 is a part of a gear.

Due to its structure, the elements that make up the line-to-ground impedance when viewed from the cord outlet where the noise suppressor 1aa or 14b (see Figures 1 and 2) of a power tool that is normally grounded is attached are: Leakage impedance of the field winding 3 of the motor, leakage impedance of the armature 2 (see Figures 1 and 2) including brush resistance, conductive parts such as the field winding 3 and the armature winding 7, and the housing. impedance due to distributed capacitance between 1 and 1. Of these, 1115~
In the 5 MHz frequency range, the main factors are the leakage impedance of the field winding 3, the impedance between the field winding 3 and the housing 1, and the impedance between the electric machine prewinding 7!7 and the housing 1. By the way, if an insulating layer 15 is provided between the armature core 6 and the rotating shaft 8 as in the embodiment shown in FIG.
The impedance due to the distributed capacitance between the armature winding 7 and the housing 1 can be made high.

The power tool impedance between wire and ground of a power tool using an electric motor with the structure shown in FIG. 8 is shown in FIG. 7.
01 curve. Comparing aJ-0, the inflection point F1 shifts to the high frequency side with the inflection p F1/, and
rL15~(The absolute value of the power tool impedance is large in the sensible wave number range of 18 MHz.

Figure 9 VC shows the noise prevention effect of the noise preventers 4a and 4b when a power tool using an electric motor having the structure shown in Figures 6 and 8 is connected as shown in Figure 1 or 2. . In Fig. 9, the 6th curve is the one in Fig. 6, and if the 0 curve is connected as in Fig. 1, the 0th curve is the one in Fig. 6.
When the wires are connected as shown in the figure, the f curve is the one in Figure 8 according to the present invention, and when the wire is connected as in Figure 1, the 6 curve is the one in Figure 8, and as in Figure 2. The noise prevention effect of a power tool using a motor with the structure shown in Fig. 11a is compared with that of a conventional power tool using a motor with the structure shown in Fig. 6. Even if the wires are connected as shown in FIG. 1 or as shown in FIG. 2, the prevention effect is improved by 15 to 30 dB.

As described above, according to the embodiments of the present invention, the impedance between the wire and the ground viewed from the installation position of the noise suppressor of the power tool can be made high in the low frequency range of [115 to [18 MHz], and the impedance Since the inflection point where the voltage changes from capacitive to conductive can be shifted to the high frequency side,
In particular, it is possible to effectively suppress noise in the frequency range α15 to α8MHtx, which generates high noise.

10 and 11 are schematic structural diagrams corresponding to FIG. 8 showing other embodiments of the present invention, and the same parts as in FIG. 8 are indicated by the same reference numerals. In FIG. 10, an insulating layer 16 is inserted between the field core 5 and the housing 1.
In the figure, an insulating layer 15 is inserted between the armature core 6 and the rotating shaft 8, and an insulating layer 16 is further inserted between the field core 5 and the casing 1. Even if the configuration is as shown in FIG. 10 or 11, the same effect as in the case of FIG. 8 can be obtained.

Further, a second housing is provided, an insulating layer is provided between the entire motor and the second housing, and the rotating shaft 8 or a part of the gear 1 is provided.
Part or all of 4 may be an insulator, and the second body may be grounded. This is equivalent to FIG. 11 and is included in the present invention.

As explained above, according to the present invention, [115-18
This has the effect of reducing line-to-earth noise in the MHz frequency range.

[Brief explanation of drawings]

Figures 1 and 2 are circuit diagrams for suppressing noise from grounded power tools, Figure 3 is an equivalent circuit diagram to explain the noise prevention effect, and Figures 4 and 5. are the first
, an equivalent circuit diagram corresponding to FIG. 3 of FIG. 2, FIG.
Figure 8 is a diagram showing frequency characteristics of impedance phase angle and impedance absolute value, Figure 8 is a diagram showing the grinding structure of an embodiment of the motor part of the grounded power tool of the present invention, and Figure 9 is a diagram showing frequency characteristics of impedance phase angle and impedance absolute value.
The figure is a diagram showing the noise prevention effect, and FIGS. 10 and 11 are schematic structural diagrams corresponding to FIG. 8 showing other embodiments of the present invention. 1... Housing, 2... Armature, 3... Field winding, 4
a. 4b... Noise preventer, 5... Field iron core, 6... Armature core, 7... Armature winding, 8... Rotating shaft, 15
．． 16...Insulating layer. Saij figure'1=2 figure h f5 figure Sai4 figure Purple5 Kunio6 figure off 0; Enko face (肱) SaiB figure Sai9r21 /Z lυ

Claims (1)

[Claims] t 1td equipped with a noise suppressor that is used by grounding the casing.
7. A grounded electric tool driven by a J-machine, characterized in that at least one of a field core and an armature core of the electric motor is electrically insulated from the casing. tool.