US2339829A - Power operator - Google Patents

Description

Jan. 25, 1944. I J u ous 2,339,829

POWER OPERATOR Filed Jan. 29, 1942 INVENTOR v Jam 27a 1621720145? ATTORNEYS Patented Jan. 25, 1944 POWER OPERATOR Joseph Youhouse, Fairfleld, Conn assignor to Casco Products Corporation, Bridgeport, Conn.,

a corporation of Connecticut Application January 29, 1942, Serial No. 428,663

12 Claims.

This invention relates to improvements in .power operators for handheld portable tools of the type disclosed and claimed in my copending application Serial No. 358,875, filed September 28, 1940, now Patent No. 2,277,264, Mar. 24, 1942, of which this application is a continuation-in- In tools of this type, a controlled power means or motor is used to drive the tool, and means is provided for interconnecting the drive shaft for the tool and the casing for the power means, whereby the shaft is held against rotation. The interconnecting means may be releasably held in operative position so that the shaft is locked while the operator has both hands free during the manipulation of the chuck or other tool-receiving means to receive and hold a tool.

Because of unfamiliarity with the structure and operation of the device or through inadvertance, a user of the device may turn on the motor while the shaft and casing are interlocked,

with the result that the motor would become overheated and damaged before such person became aware of the trouble. Or, if the plug on the cord has been removed from the socket to stop the operation of the motor while the switch is in the "on position, and the chuck locking means has been moved to locked position in order to change a tool while the device is disconnected from the source of energy, when it is again plugged in, the armature, being locked, might become overloaded and greatly overheated, with the possibility of burning-out before the error is noted.

Also, during the operation of the tool, inexperienced users of the device might use it in such a manner as to stall it and thus overload the motor and cause it to heat up and damage parts thereof.

These dimculties have been overcome by the present invention by providing a protecting means to open the motor circuit to prevent a damaging operation thereof upon its connection to a power supply while the shaft is held against rotation or upon an abnormal load condition.

Since the motor and its casing must be relatively small so that it can be conveniently held in the hand, the space in which the protecting means may be mounted is very limited. According to the present preferred embodiment of the invention, a novel arrangement of switch parts is provided within the casing and positioned on the usual switch mounting carrying the controlling switch for the motor. This protecting switch means is operative to open the motor circuit upon an abnormal condition.

a screw I6.

Preferably, the protecting switch device of this invention is heat responsive and is located in very close proximity with the motor. The switch, being closely confined by the casing, can be made to operate either by heat generated by the current passing therethrough, by heat transmitted from the motor, or by both of these conditions.

In the broader aspects, the present invention provides, in combination with a power driven shaft adapted to be locked against rotation, a means for preventing damaging operation of the power means while the shaft is locked against rotation.v

A feature of the present invention resides in the simplicity of the structure, ease of installation, and its effective control.

Other features and advantages of the invention will be apparent from the specification and claims when considered in connection with the drawing, in which:

Figure 1 shows a longitudinal sectional view of the casing.

Fig. 2 is a sectional view taken along lines 22 of Fig. 1.

Fig. 3 is a detail perspective view of the switch un Fig. 4 is a detailed sectional view of the conical collar taken along line 4-4 of Fig. 1 with the sleeve in retracted position therein and in engagement with the latching means.

t Ft'ig. 5 is a perspective view of the bridging con- Fig. 6 shows a circuit diagram including a diagrammatical view of the switch.

The present invention has been illustrated as applied to a portable tool of the type disclosed in my above-noted copending application, wherein a skeleton subframe l0 carries the movable parts of the tool and a two-part casing ll closely surrounds and supports the subframe and provides a handle for the tool whereby it can be readily held in the hand and manipulated during use.

The power operator for the tool is herein shown as an electric motor having a U-shaped field structure l3 secured to the subframe with a field winding l4 disposed in the bow of the U.

A thrust piece I5 is held to the subframe by i It is disposed between the legs of the U and receives one end of the shaft ll of an armature l8 and positions the armature between the pole pieces l3a on each leg of the U, The other end of the armature shaft is supported in bearings carried by a collar portion 20 of the subframe and extends beyond the end thereof to receive a chuck or tool-receiving means II. The collar portion also carries the brushes Ila for the motor.

The casing closely surrounds the motor and the motor control is mounted in the limited space available and comprises a switch plate 22 having a heat-responsive switch 40 connected in the motor circuit. The switch is mounted on the switch plate 22, and, as shown in Figs. 1 and 2, lies in juxtaposition with the armature. The switch comprises a T-shaped member having the head 4| of the T secured to the plate while the part 42 of the T, which is formed as an arm of bimetallic material, extends toward the switch contact 28 which is provided with an ear-like extension 48. The extension carries a contact 44 to cooperate with a contact 45 carried by the bimetallic arm. The arm is biased in the direction to carry the contact 45 into engagement with contact 44 and normally maintains the cir- 28 to control the circuit to the motor, as will be a later explained.

A truncate collar 29 is threaded on the reduced neck 30 of the collar portion of the subframe and extends part way along the tool-receiving means. The truncate collar carries a slidable sleeve 3| which is urged by a spring 32 to extend beyond the end of the collar to completely enclose the chuck or tool-receiving means, including, the operator Zia therefor as shown in Fig. 1. The sleeve is normallyheld against rotation during use by a key 33 operating in a keyway 34 on the inner wall of the truncated collar 29.

When it is desired to change or install a tool, the sleeve is moved back against the urge of the spring, until teeth 35 carried thereby engage with cooperating teeth 36 carried by the shaft to interconnect the shaft and casing and hold the shaft against rotation.

As shown in Fig. 4, the keyway hasa lateral recess 3'! and notch 38 for receiving the key upon slight turning of the sleeve to releasably hold the sleeve in its retracted position. The spring, it will be noted, urges the key into the notch 38 and prevents unintentional release thereof so that the operator has both hands free to manipulate the chuck to engage or release a tool without being required to hold the sleeve against the urging means. As long as the sleeve remains in itsretracted position, the shaft and the armature thereon will be interconnected with the casing and held against rotation.

Persons who are not familiar with the structure or operation of the device may plug in the tool or otherwise connect the motor to a suitable source of energy, while the shaft is thus locked against rotation. Since the armature cannot rotate, it will draw a heavy current and become greatly overloaded without the attention of the user being called to the fact that it is so overloaded and the motor may be damaged or even burned out.

Then, too, persons who are familiar with the device may inadvertently turn on the switch while the sleeve is in retracted position. Since the shaft cannot rotate, the person will not have any indication that the power is on and the overload caused by the locked armature will cause the motor toburn out.

To prevent such occurrences, the present invention provides a protecting means which opens the circuit to the motor before it can be damaged by such improper use.

In applying a protective means to a device of the type described, which is very compact and has its casing closely embracing the motor, diiiiculty was encountered in locating the means.

In the preferred illustrated form of the invention, the protecting means has been embodied in cuit therethrough closed.

The head of the T is provided with a terminal 40 to which is connected one of the leads 41 of the motor so that the circuit for the motor extends through the terminal and the bimetallic arm 42 to the switch contact 28. The contact 25 is connected to another lead 48 of the motor so that the circuit to the motor is completed when the bridging member is moved into its back position as shown in dot and dash lines in Fig. '1 and engages both contacts.

The switch is provided with a detent member 48 which cooperates with the bridging member to hold it in either the closed or open-circuit position.

It will be noted from Fig. 2 that the heat- I responsive switch member is disposed in close proximity to the armature and is closely confined by the casing, so, that the arm 42 of the switch may be effectively heated by heat transmitted from the armature. Also, the arm may be so designed as to be heated by heat generated therein by an abnormal flow of current therethrough. If desired, the arm could be partially heated by both of these methods so that the temperature of the motor does not exceed a safe limit which will be above the normal temperature of the tool, but lower than the critical temperature which might damage the windings of the motor, or the bearings or other parts of the device.

Thus, if the circuit is closed while the shaft is held against rotation, the armature will draw an abnormally high current in an effort to rotate said shaft. This will cause the thermostat to be heated and it will flex outwardly and away from ear 4! so as to break the motor circuit between the contacts 44, 45.

When the thermostat has cooled down, the circuit will again be made and the operation repeated until the motor is disconnected or the shaft freed for rotation.

Further, in using the tool in grinding or other operations, if an undue load is placed thereon,

' which tends to stall the motor and prevent the shaft from rotating, the motor will become heated and theprotective device of the present invention, being heated by the motor, will be opened before damage can occur.

The switch of the present invention comprises essentially a single operator which can be readily mounted on the usual switch plate when the motor control switch is assembled thereon without enlarging or greatly altering the plate, and can be readily installed in the space provided for said switch plate without in any way changing the size and shape of the casing.

In the broader aspects of the present invention, I have provided in the combination of a power operator and means which locks the shaft thereof against rotation, of a protective means which prevents damage to the motor in the event that it is actuated before the locking means for the shaft has been released.

Variations and modifications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1. In a portable power-operated tool, an electric motor having a shaft; a casing surrounding said motor; tool-receiving means on the shaft; means for releasably interconnecting said shaft and casing to hold the shaft against rotation; switch means on said casing in; connecting said motor to a source of power; and separate switch means for opening the circuit to said motor upon the same being connected to the source of power prior to the release of the locking means and while the shaft is interconnected to the casing.

2. In a power-operated tool, an electric motor having a shaft; a casing surrounding said motor; tool-receiving means on the shaft; means for interconnecting said shaft and casing to hold the shaft against rotation; means for releasably locking said means in interconnecting position; means for connecting said motor to a source of power; and separate means for opening the circuit to said motor and preventing damage thereto by being connected to the source of power prior to the release of the locking means and the interconnection of the shaft to the casing.

3. In a tool of the type described, an electric motor having an armature and tool-carrying shaft; a casing closely surrounding said motor and supporting the same; means for releasably locking said shaft against rotation; means for connecting the motor to a source of power; and heat-responsive switch means connected in the motor circuit and confined within the casing in close proximity to the armature of the motor to be heated therefrom upon energization of said motor while the shaft is locked against rotation to automatically open the circuit to the motor.

4. In a portable power-operated tool, an electric motor having a shaft; a casing surrounding said motor; tool-receiving means on the shaft; means for interconnecting said shaft and casing to hold the shaft against rotation; means for releasably locking said means in interconnecting position; and means for connecting said motor to a source of power, including a separate heat-responsive switch means disposed within the casing for opening the circuit to said motor upon the same becoming overheated by being connected to the source of power with the shaft in interconnected relation prior to the release of the locking means.

5. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on the shaft; a switch plate of insulating material mounted within the casing and having contacts thereon adapted to be manually closed to connect said motor to a source of power, one of said contacts having an ear projecting therefrom; and a bimetallic arm having one end secured to the switch plate and connected in the motor circuit and the other end of the arm engaging the ear and forming a heat-responsive switch in the motor circuit, said switch being in heat-receiving relation with said motor to be heated by heat generated therein in response to an overload on said motor and flexing to automatically open the circuit to said motor.

6. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surround said motor; tool-receiving means on the an overloading of said motor and flexing to open the circuit.

7. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on the shaft; a switch plate of insulating material mounted within the casing and having contacts thereon adapted to be manually closed to connect said motor to a source of power, one of said contacts having an ear projecting therefrom; and a bimetallic arm having one end secured to the switch plate and connected in the motor circuit and the other end of the arm engaging the ear and forming a heat-responsive switch in the motor circuit, said switch being in heat-receiving relation with said motor to be heated by heat transmitted therefrom and by heat generated by the current passing therethrough upon an overload on said motor and flexing to open said circuit. 4 8. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on the shaft; an elongate switch plate mounted within and closely confined by the casing and having a pair of spaced contacts thereon; a bridging contact carried by the casing and adapted to be manually moved to connect said contacts; and an auxiliary heat-responsive switch comprising a bimetallic arm mounted on the switch plate and engaging one of the spaced contacts, the other spaced contact and the bimetallic arm being connected in the motor circuit whereby when said spaced contacts are bridged the circuit to the motor through the heat-responsive switch will be closed, said heat-responsive switch being heated in response to an overloading of said motor to open the circuit thereto.

9. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on the shaft; means carried by the casing for releasably locking said shaft against rotation; an elongate switch plate mounted within and closely confined by the casing and having a pair of spaced contacts thereon; a bridging contact carried by the casing and adaptedto be manually moved to connect said contacts; and an auxiliary heat-responsive switch comprising a bimetallic arm mounted on the switch plate and engaging one of the spaced contacts, the other spaced contact and the bimetallic arm being connected in the motor circuit whereby when said spaced contacts are bridged the circuit to the motor through the heat-responsive switch will be closed, said heat-responsive switch being in heatreceiving relation with said motor and heated thereby in response to an overloading of said motor, upon failure to release the shaft lock, to open the circuit thereto.

10. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on casing and having contacts thereon adapted to be manually closed to connect said motor to a source of power; and an auxiliary heat-responsive switch mounted on the switch plate and connected in the circuit to said motor to be heated in response to an overload on said motor and open said circuit.

11. In a device of the type described, an electric motor having an armature; a casing closely surrounding said motor and supporting the same; means for releasably locking the armature against rotation; a switch means disposed within the casing and connected in the motor circuit for controlling the energization of said motor; a manual operator extending through said casing for actuating said switch means; and auxiliary switch means connected in the motor circuit and disposed within the casing in close proximity to the armature, means being heat-responsive and heated by heat generated in and transmitted from said arma said auxiliary switch 2,389,829 the shaft; a switch plate mounted within the ture to automatically open the circuit to the motor upon energization thereot while said armature is locked against rotation.

12. In a handheld power-operated tool, an electric motor having a shaft; a casing closely surrounding said motor; tool-receiving means on the shaft; a switch plate of insulating material casing and having a pair of spaced contacts thereon, one contact being connected to the source of current; a bimetallic arm having one end secured to the switch plate and connected to the motor circuit and the other end of the arm normally engaging a portion of the other spaced contact and forming therein a heat-responsive switch in the motor circuit, the circuit at the spaced contacts being adapted to be manually closed to connect the motor to a source of power and said heat-responsive switch being heated in response to an overload 01 said motor to flex and open the circuit thereto.

JOSEPH YOUHOUSE.

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