Measuring Instrument for Friction Torque of Needle Ｒoller Bearings

Abstract: Aiming at the problems in measurement of friction torque of needle roller bearings，the measuring instrument is developed for friction torque of needle roller bearings． The instrument is able to apply radial load to needle roller bearings，and the multi － point measurement of friction torque can be carried out，making users to comprehensively analyze variation situation of friction torque．

Key words: needle roller bearing; friction torque; measuring instrument

Needle roller bearings have a compact radial structure and can only withstand radial loads, making them particularly suitable for support structures with limited radial installation dimensions. According to the usage situation, bearings without inner rings or needle roller and cage components can be selected. When subjected to radial load, the friction torque of needle roller bearings is a variable, and the influencing factors are quite complex, which may differ significantly when measured repeatedly. To achieve relatively stable friction performance, scientific analysis should be conducted based on the measurement results of the product and the friction torque variation curve. The traditional friction torque measurement method (hanging weight measurement method) can achieve high detection accuracy, but the measurement efficiency is low and cannot reflect the change curve of friction torque, which cannot meet the measurement needs of friction torque. Therefore, a friction torque measuring instrument for needle roller bearings was developed.

1. Measurement principle

The measurement principle of the instrument is the balance method, which applies a balance torque of equal magnitude and opposite direction to the measured bearing, and reflects the change in the actual friction torque of the measured bearing through its changes. The measurement principle is shown in Figure 1. The tested bearing is installed on the drive shaft. When the inner ring (needle roller) rotates at low speed, the friction torque drives the outer ring of the bearing to rotate due to the presence of friction inside the bearing; The outer ring of the tested bearing is connected to the torque sensor through a measuring ring, and the measuring rod of the torque sensor hinders the rotation of the outer ring and balances with the internal friction moment of the bearing; The torque sensor converts the bearing friction torque into an electrical signal, which is amplified and analog-to-digital converted before being transmitted to a computer. After data processing, six measurement results, including the maximum torque value, average torque value, and torque difference in forward and reverse directions, as well as the forward and reverse friction torque variation curves, are obtained.

Figure 1 Schematic diagram of measurement principle

2. Mechanical structure

The mechanical structure of the instrument is shown in Figure 2, which is mainly divided into a driving part, a measuring part, and a rotating part.

The driving part consists of a driving motor and a driving shaft system. The driving motor (DC synchronous motor) is connected to the driving shaft system through a synchronous pulley, driving the driving shaft system to rotate.

The measurement part consists of a needle roller bearing, a measuring ring, a measuring spindle, and a torque sensor. The needle roller bearing is installed on the drive shaft system through a measuring spindle, and the measuring ring is sleeved on the outer ring of the bearing and connected to the measuring rod of the torque sensor.

The rotating part consists of a rotating electric motor and a lever. The rotating electric motor (stepper motor) moves the measuring ring through the lever, driving the outer ring of the bearing to rotate at a certain angle, achieving multi-point measurement.

During measurement, the torque sensor is fixed on guide rail A and connected to the measuring ring; After positioning guide rail B, push and rotate the motor to the working position, so that the lever can reach the position where the measuring ring can be moved; The drive motor drives the shaft system to rotate, causing the spindle to drive the needle roller to rotate, thereby driving the outer ring to rotate; The torque sensor hinders the rotation of the outer ring and maintains dynamic balance with the friction torque of the needle bearing. Its output is the friction torque of the needle bearing, completing a measurement process. After the measurement is completed, exit the rotating motor, remove the measuring ring, and remove the needle bearing.

1- Drive motor; 2- Drive shaft system; 3- Torque sensor; 4- Guide rail A; 5- Measurement ring; 6- Needle roller bearing; 7- Paddle; 8- Rotating electric motor; 9- Guide rail B

Figure 2 Mechanical Structure Diagram

3. Measurement Key Points

3.1 Positioning of needle roller bearings

To ensure good contact and positioning between the rolling needle and the measuring spindle, the measuring spindle is designed in a form similar to a spring clamp. As shown in Figure 3, a conical hole is machined on the measuring spindle head, and the clamp head is used to fit with the conical hole, causing the spindle head to expand and deform slightly, thereby making the measuring spindle and the rolling needle closely fit and locate.

It should be noted that at this point, the surface of the measuring spindle is directly used as the rolling surface of the bearing needle. To ensure the same load-bearing and operating performance as bearings with a ring, the hardness, machining accuracy, and surface quality of the measuring spindle raceway surface should be similar to the raceway of the bearing ring.

1- Bearing outer ring; 2- Measurement ring; 3- Rolling needle; 4- Measurement spindle; 5- Card head; 6- Torque sensor measuring rod; 7- Torque sensor

Figure 3 Bearing positioning diagram

3.2 Radial loading

During measurement, a certain radial load needs to be applied to the tested bearing. The radial load is determined based on the specific bearing model, and its size is the self weight of the measuring ring.

3.3 Multipoint measurement process

The radial load is applied by the self weight of the measuring ring, which can easily cause uneven force on the measured shaft. Only single point measurement cannot truly reflect the torque change of the bearing. Therefore, one point is selected every 90 ° on the outer ring for measurement.

As shown in Figure 4, there are 8 grooves on the measuring ring, and any one of them is taken as the measuring point. After the measurement is completed, remove the torque sensor to detach the sensor rod from the measurement slot. Then, the electrical system controls the rotating motor to drive the lever to rotate. The measuring ring (bearing outer ring) rotates by 90 ° and detaches from the slot to avoid introducing additional torque. The sensor rod extends into the measurement slot through guide rail A and enters the next point for measurement.

Figure 4 Schematic diagram of measuring ring

4. Instrument calibration

The calibration of the instrument adopts the method of comparing the input standard torque value with the actual output measurement value of the instrument. The designed specialized calibration and identification device is shown in Figure 6. The calibration spindle is installed on the shaft system and tightened with screws. The calibration bearing (model 618/3) and calibration wheel are installed on the calibration spindle. The sensor measuring rod is pushed to the measurement position and connected to the calibration wheel. The standard weight force is applied to the calibration wheel by a wire, and the standard weight and calibration wheel radius are used as input standard torque. The sensor output torque is the actual measured value. The measurement accuracy is the difference between the standard torque M (M=0.009 8FL) calculated by multiplying the force arm L and the weight mass F, and the instrument measurement value M0. The accuracy of the lever arm L is ± 0.01, and the weight quality accuracy level is M3, which can meet the accuracy requirements. Calculate the standard torque values corresponding to the weight based on its mass and the radius of the weight wheel.

1- Calibration wheel; 2- Calibrate bearings; 3- Calibration spindle; 4- Sensor measuring rod; 5- Weights

Figure 5 Calibration diagram

5. Conclusion

The design of the needle roller bearing friction torque measuring instrument is reasonable, with a high degree of automation. It can measure multiple points and display the change curve of friction torque, making it easy for users to intuitively and comprehensively analyze the changes in friction torque.

More about KYOCM Slewing Bearing ：

Rotary bearings consist of an inner ring and an outer ring, one of which usually contains a gear. Together with the connecting holes in the two rings, they enable optimized power transmission through simple and fast connections between adjacent machine parts. Bearing raceways are designed with rolling elements, cages or gaskets to accommodate loads acting individually or in combination in any direction.

Features and advantages:

High carrying capacity

High stiffness for rigid bearing applications

Low friction

Long service life

Surface protection and corrosion resistance

Integrate other features including:

Driving mechanism

Control device

Lubrication system

Monitoring system

Sealed cassette tape

https://www.kyocm.com/products/Slewing-Bearing/745.html