Description:FIELD OF THE INVENTION:
[0001] The present invention relates generally to a measurement system that is used to measure minimum breakaway torque of self-locking nut automatically.

BACKGROUND OF THE INVENTION:
[0002] Torque is the angular force needed to turn or rotate an object. A simple example would be rotating a nut to tighten onto a bolt. From gauging the output of a ship's engine to regulating the tightness of a soft drink bottle cap, torque is evaluated in a variety of applications. However, the majority of torque applications involve the management of fasteners with threads. The fastener must exert such a powerful clamping force that the pieces of material cannot separate while the assembled product is being used. Lock nuts, which were first developed in the 1930s, provide a simpler and more affordable way to prevent vibration-related loosening. Traditional nuts are just a simple threaded hole, therefore prolonged exposure to vibrations can cause them to come loose from the bolt they are attached to. But lock nuts prevent loosening by having a design feature that makes the nut more vibration-resistant. Understanding the lock nut’s tightening torque is critical in designing the locking feature. It is a challenging task as it depends on the material used, friction and the load conditions. If the nut fails during a critical operation in a machinery, it may result in operator injury and further costs will be incurred. The current invention aims to provide a re-configurable measurement system for measuring and validating the breakaway torque of user defined lock nut sizes thereby ensuring the quality of the lock nuts and prevent unexpected failures during operation.

SUMMARY OF THE INVENTION:
[0003] The objective of the present innovation is to provide a torque measuring and validation system to confirm the serviceability of lock nuts of various sizes. The overall system consists of a torque testing assembly attached to a horizontal axis, a control panel and a bolt socket fixture assembly. The measurement system is a special purpose machine that inspects the breakaway torque of the lock nuts. The current system is designed to measure and validate several known breakaway torque values as shown in the table below.

Table 1 Breakaway for Self-locking Nuts
Thread Size Threads/Inch Minimum Breakaway
1/4" 28 3.5 lb in. 0.40 Nm
5/16" 24 6.5 lb in. 0.73 Nm
3/8" 24 9.5 lb in. 1.07 Nm
7/16" 20 14.0 lb in. 1.58 Nm
1/2" 20 18.0 lb in. 2.03 Nm
9/16" 18 24.0 lb in. 2.71 Nm
5/8" 18 32.0 lb in. 3.62 Nm
3/4" 16 50.0 lb in. 5.65 Nm

[004] The key component of the measurement system is the torque testing assembly which consists of a torque transducer, a servo motor coupled to a gear box, linear guide ways and a stepper motor for Z-axis movement. The socket engages with the nut (z-axis) then both the z-axis and c-axis starts rotating thereby performing screwing action. Once tightening is achieved after a number of predefined threads the peak torque is measured and compared against the standard value. The allowed tolerance range is 2% above or below the pre-set torque value corresponding to each lock nut. If measured value exceeds or is equal to the preset, the nut is “PASSED”, else it is rejected as “FAIL”. The validation will be displayed in an HMI display and the machine will unscrew the nut to the same position and wait for the operator to unload. The novelty of the system is that it can be calibrated to measure the breakaway and tightening torque of several sizes of lock nuts.

DETAILED DESCRIPTION OF THE INVENTION:
[0005] In the following description, various embodiment are explained with reference to drawings. For the purpose of understanding, specific details and configurations are set forth.
Figure 1 shows the isometric view of the torque measurement system showing the key components.
Figure 2 shows the details of the torque testing assembly.
Figure 3 illustrates system architecture and the electronic components involved.
Figure 4 shows the bolt socket fixture assembly
Figure 5 illustrates the breakaway torque measurement logic.

[0006] Figure 1 shows the isometric view of the entire measurement system with the main components. (100) and (101) are aluminum profile base and cover structures within which the entire assembly is housed. (102) is the horizontal (X-axis) gantry to which the torque measuring assembly is attached. The X-axis gantry moves left and right based on the required position of the bolt fixtures to rotate and measure the lock nut torque values. (103) is the main assembly that consists of the torque measuring transducer. (103) is mounted to (102) through lead screw mechanism and the assembly is capable of moving up and down. (104) is an HMI panel (GS 2110-WTBD-N) wherein the torque readings and results are displayed. (105) is the main controller of the system consisting of a PLC and required electronics to run the measurement system. (106) and (107) are “OK” and “NOT OK” bins to store the nuts that pass and fail the breakaway torque requirement test respectively. The entire assembly is mounted on wheels so that is moved to convenient locations within the shop floor easily.

[0007] Figure 2 shows the torque testing assembly and its components. (200) is the main torque sensor (SGR511) used to measure the torque required to rotate the lock nuts and also measure the breakaway torque. The sensor is protected by a sensor guard (202). The total sensor assembly is attached to the servo motor (HG-KN73J) through the coupling (203) and the gear box (204). The servo motor is run through separate drive (MR-JE-70C). The gear box is used to achieve speed reduction and it is attached to a servo motor (205) which is used to achieve the rotary motion of the lock nuts in turn allowing the torque sensor (200) to measure the torque values. A Stepper Motor (206) is used to achieve the Z-axis (up and down) movement of the motor and the torque sensor assembly so that the socket attached at the end engages with the lock nut and rotates it to measure the torque. The floating joint (208) is used to disengage the motor from the torque sensor if the torque exceeds than the maximum limit to protect the sensor and the motor as well. All the components from (200) to (207) described slide of a linear motion guide way (207) for steady motion. The entire assembly is attached to the X-axis gantry (102) using the base plate.

[0008] Figure 3 illustrates system architecture and the electronic components involved. The heart of the main control system (300) is the programmable logic controller (FX5U-4AD-ADP). The system consists of a 4-channel analog input module which receives input from the torque sensor. The PLC processes the information from the torque transducer and process the same to validate the breakaway torque of the lock nuts. The servo motors and the HMI are controlled by the PLC.

[0009] Figure 4 shows the bolt socket fixture assembly. The fixture holds the bolt (400) and socket (401) required for a specific lock nut. (400) and (401) is attached to a socket adapter (402) which is fixed for a specific lock nut size. The entire socket fixture assembly is fixed to the bed of the measurement system using a base plate (404). In the current system, totally 11 socket adapters are available catering to different lock nut sizes with different breakaway torques. The system is customizable for adapting to lock nuts of different sizes also besides the standard sizes provided currently.

[0010] Figure 5 illustrates the breakaway torque measurement logic. For the operation to start, the user has to load the lock nuts of various sizes at their respective stations. Once loaded, the cycle starts by moving the X-axis to the selected station which consists of the bolt and nut assembly whose breakaway torque is required. The Z-axis moves down with the appropriate socket and starts tightening the nut. There are two measuring modes programmed in the controller.
a) To measure tightening torque – the lock nut is rotated until the locking is achieved. The value measured during the rotation provided the tightening torque.
b) The measure breakaway torque – lock nut is rotated until locking and rotated back in the opposite direction to measure the breakaway torque. If the measured torque is above the pre-set value, the but is “PASSED” and marked as serviceable; and if the value is below the pre-set value, the nut “FAILS” and marked as non-serviceable.
Once the required data is acquired and the results are viewed by the user, the nut is unscrewed and the Z-axis is moved up. The cycle ends with the X-axis being moved to its home position.

[0011] The above embodiment are described for the way of measuring the tightening and breakaway torque using the developed torque measurement system. The measurement system is currently calibrated for 0.40 Nm,0.73 Nm,1.07 Nm, 1.58 Nm, 2.03 Nm, 2.71 Nm, 3.62 Nm and 5.65 Nm torque values. The system can be extended to accommodate various lock nuts with different breakaway values mentioned above.
, Claims:1. An automatic, special purpose, re-configurable torque measurement system consisting of a torque testing assembly attached to a horizontal axis, a bolt socket fixture assembly, a PLC, HMI panel and a controller.

2. The bolt socket fixture assembly set forth in claim 1 is an original design that can accommodate lock nuts of various sizes with different tightening and breakaway torques.

3. The bolt socket fixture assembly set forth in claim 2 can be reconfigured to a circular pattern or any other user defined requirement.

4. The torque testing assembly set forth in claim 1 with the capability of measuring and validating the breakaway torques of different lock nut sizes within the user defined range