Tube wrench

Abstract: A separate thumb accessible pushbutton (35) operated circuit reverses a motor operated tube nut wrench at a reduced speed to intercept a home stop cam (14), after which the wrench is automatically shut off on sensing a current rise in the motor on stall to avoid over stress and unnecessary heat build-up.

Description: This invention relates generally to power driven nutrunners and more particularly to direct current tube nut wrenches which require the operator to switch the tool in reverse returning the drive to its home position and then switch it back to forward for the next tube nut. Some of the present wrenches return the drive at full power which causes excessive stress and wear in the return mechanism. In addition, if the wrench continues to be activated upon return to the home position, excessive heat build-up can be generated in the stalled motor device. FR-A-2 253 606 discloses a screwing apparatus which can be a tube torque wrench in accordance with the preamble of claim 1. According to the present invention there is provided a tube wrench comprising an electric motor power driven wrench providing rotational output on a tube nut drive head of the type which receives a tube within its confines in one rotary orientation and captures a nut on said tube in a second rotary operating position during a tightening process of said nut; characterised in that said electric motor is a D.C. motor and means are provided for operating said power driven wrench in a reverse drive mode, said reverse drive mode means including a reverse drive initiating means for initiating reverse rotation of said nut drive head to a first tube receiving position limited by a mechanical stop engageable in the reverse direction; a means for sensing arrival at said stop and shutting said reverse rotation off, and said means for sensing arrival at said stop and shutting said reverse rotation off comprises a circuit for sensing current rise in said electric motor at said stop. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a plan view of a DC electric assembly tool of the tube nut wrench variety; Fig. 2 is a side view of the DC tube nut wrench; Fig. 3 is a control schematic for the tube nut wrench; Fig. 4 is an exploded view of a nut drive head; and Fig. 5 is an end view of an input spindle gear of the nut drive head showing a reverse stop cam. In Figures 1 and 2, a DC angle wrench is generally shown and indicated by the reference numeral 20. The wrench is fitted with a tube nut head 25 attached to an angle head drive 21 which in turn is attached to a gear reduction housing 22, a motor housing 23 and a handle 24. The angle wrench is further provided with a control and power cable 26 attached to the end of the handle. The angle wrench has a forward throttle handle 30 (seen in Fig. 2) and a reverse actuating switch 35. The forward throttle is conveniently located to be activated by the user's fingers and the reverse actuating switch 35 is placed so that it may be conveniently operated by the user's thumb. In operation, a DC motor enclosed within the motor housing 23 drives through reduction gears the angle head and tube nut head to tighten a tube nut. Once the tube nut reaches the desired torque a transducer sends a signal through the control cable and the DC motor is shut off. The operator then slides the tube nut head off the tube nut up on to the tubing. Unless the tube nut happens to stop in the home position, the operator must then depress the reverse actuating switch 35 which reverse drives the head back to the home position. When the head reaches the home position the ratchet mechanism latches and the reverse torque begins to rise. As the torque rises, a specialised circuit as shown in Fig. 3 senses a rise in the current of the motor and shuts the tool off by disengaging the throttle. The operator can then remove the tube nut head off the tubing. The circuit, shown in Fig. 3, performs the task of reversing the tool until the home or index position is reached. It also locks out the tool throttle during this operation and provides a slight delay before reversing the tool until a system calibration check can be completed on the transducer and associated signal conditioning circuitry as is done immediately following any rundown. The circuit ensures that the tool is reversed slowly and shut down immediately once the home position is reached, or if the operator chooses to release the reverse button at any time, the reverse operation may be discontinued. Motor current is used to sense the torque increase in the reverse position. This occurs when the tool reaches the home position. Motor current is used because the normal forward reading torque transducer is calibrated in the forward direction only. The reversing torque is not required to be high unless specifically called for in untightening the nut. A lower home drive torque and the slower speed of operation were thus major considerations of the circuit design. The homing design circuit, shown in Fig. 3, consists of the following components and operation: Relay 40 serves to lock out the throttle immediately whenever the reverse button is engaged. A specific time lag is created by the values of capacitor 41 and resistor 42 through signal buffers 43, 44 and 45, before slow reverse action is initiated and held by latch 46, by turning transistor 47 on. Resistors 48 and 49, which may also be replaced by a potentiometer to allow adjustment, set the current level trip point at which the motor will be shut down. A voltage signal representative of the motor current is brought through limiting components 50 and 51 and filtered by a capacitor 52. Comparator 53 compares the present motor current to the trip level setpoint and resets latch 46 when the proper current is obtained. Note that this reset only occurs if the tool is indeed in reverse due to the logic of buffer 54. When the latch is reset transistor 47 is turned off, the motor enable signal is disabled to earth via resistor 55 and the motor is stopped. Connectors (not shown) bring the necessary signals for the tool throttle motor current and reverse to and from the specialised circuit. Fig. 4 shows an exploded view of a gear offset head comprising a housing bottom part 1 which constitutes the frame for the gear offset head, a housing top part 2 or cap which encloses the bottom part and retains the working parts of the head which includes a rotary input spindle gear 3 having a reverse stop cam 9 on its far side, as partially shown in Fig. 4, and best seen in end view in Fig. 5. The input spindle gear rotates on a shaft 7 and in turn drives the intermediate gear 4 which is part of a pair of gears of which only one is shown. The intermediate gear 4 rotates on shaft 8 and in turn drives the output gear 15 which contains the nut jaw for the tube wrench. The assembly is held together and mounted to the angle head drive 21 by means of a series of four adapter cap screws 11. A cavity 12 adjacent the input spindle gear contains a reverse stop pawl 5 which is spring loaded to contact the reverse stop cam 9 by means of a spring 6. It will be appreciated that the reverse pawl simply rides up over the reverse stop cam in the forward direction to permit rotation. In the reverse direction (clockwise as viewed in Fig. 5), the stop pawl intercepts the stop pawl abutment 14 to prevent reverse rotation at the predetermined point which aligns the output gear jaw with the opening 16 provided in the geared head housing. The stop, as previously described, is provided as an alignment means permitting insertion and withdrawal of the tube nut wrench about the tube.

Claims: A tube wrench (20) comprising an electric motor power driven wrench providing rotational output on a tube nut drive head (25) of the type which receives a tube within its confines in one rotary orientation and captures a nut on said tube in a second rotary operating position during a tightening process of said nut; characterised in that said electric motor is a D.C. motor and means are provided for operating said power driven wrench in a reverse drive mode, said reverse drive mode means including a reverse drive initiating means (35) for initiating reverse rotation of said nut drive head (25) to a first tube receiving position limited by a mechanical stop (9) engageable in the reverse direction; a means for sensing arrival at said stop and shutting said reverse rotation off, and said means for sensing arrival at said stop (9) and shutting said reverse rotation off comprises a circuit (Fig. 3) for sensing current rise in said electric motor at said stop. A tube wrench according to claim 1, wherein said reverse drive initiating means for initiating reverse rotation of said nut drive head includes a reverse switch (35) independent of a forward drive select throttle switch (30). A tube wrench according to claim 1 or 2, wherein said means for sensing arrival at said stop and shutting said reverse rotation off comprises a circuit independent of a circuit for control of said power driven wrench in a tube nut tightening function.

Inventors: ESTEP JOHN M, MORRIS III HARRY E, WARNER DONALD R, ESTEP, JOHN M., MORRIS III, HARRY E., WARNER, DONALD R.
Applicants: INGERSOLL RAND CO, INGERSOLL-RAND COMPANY
Application year: 1995
Main classification: B25B21
IPC codes: B25B21