Abstract: A kind of device is introduced, which can automatically detect the diameter of steel balls of bearings and sort them. The inductive transducer intelligent measuring system and traction electromagnet device are adopted, and the measurement of diameter for steel balls and sorting work are automated. The mechanical control parts and PLC control system for the device are analyzed in detail.
Key words: rolling bearing; steel ball; sorting; inductive transducer; electromagnet; PLC
The diameter of the steel ball directly affects the dynamic working characteristics of the bearing. Therefore, detecting and sorting the diameter of the steel ball before installation is of great practical significance for ball bearings. In the past, manual sorting of steel balls was mainly used, which resulted in high labor intensity, low work efficiency, and poor sorting accuracy. The following is a detailed introduction to the design of an automatic detection and sorting device for bearing steel balls with a diameter of (9 ± 0.003) mm.
1. Structure and working principle
The automatic measurement and sorting device for steel balls is shown in Figure 1, which mainly includes pneumatic transmission device, inductance micrometer device, electromagnetic flap device, and PLC control system. Use a pneumatic transmission device to send the steel ball to the corresponding testing workbench, select an inductance sensor as the signal pickup source, and use the internal measurement circuit of the inductance micrometer device to detect the micro displacement signal of the steel ball diameter and convert it into a voltage signal that is convenient for transmission, processing, and display. According to different voltage signals, the PLC controls the corresponding electromagnetic iron of the receiving box to be energized, opens the corresponding box flap, and causes the steel balls to fall into the receiving box, achieving the goal of efficient and accurate sorting of steel balls.
Cylinder; 2- Stop block; 3- Inductive micrometer device; 4- Spring baffle; 5- Material box flap; 6-Electromagnet
Figure 1: Schematic diagram of the structure of the steel ball diameter measurement and sorting device
2. Mechanical control part design
2.1 Power mechanism
Given the design requirement of continuously and accurately measuring the diameter of the steel ball, the power mechanism is required to continuously transmit the steel ball to the measuring mechanism. This type of transmission mechanism has two types: electrical and pneumatic. The electrical transmission is unstable, while the fixed cylinder transmission in pneumatic transmission is suitable for precise measurement. Therefore, a single piston rod double acting cylinder is selected. According to different installation methods, cylinders can be divided into piston rod fixed type and cylinder barrel fixed type. Considering the volume requirements of the design device, foot mounted cylinder barrel fixed type cylinders are adopted. As shown in Figure 1, the cylinder piston rod is connected to the stopper, and the steel ball comes out of the discharge port and falls into the groove of the stopper. With the help of the spring baffle on the workbench, the steel ball is fixed; At this point, the stopper moves forward not only to block the discharge port, but also to push the steel ball forward and reach the measurement position for testing; After the measurement is completed, the cylinder continues to push the stopper until the spring baffle cannot block the steel ball, and the steel ball falls into the corresponding receiving box; The cylinder returns and the spring baffle automatically returns to its initial state.
2.2 Automatic measuring device
The automatic measurement device mainly consists of inductive sensors and measurement circuits. The device adopts a linear differential inductance sensor, which is mainly composed of movable armature, primary winding, and 2 secondary windings. Due to the up and down movement of the armature, the mutual inductance between the primary and secondary windings will change accordingly. When using, two secondary windings should be connected in reverse series to achieve differential output. The magnetic circuit size and parameters of the two secondary coils should be equal.
Differential inductance sensor uses the principle of electromagnetic induction to convert the measured physical quantity into a change in the mutual inductance coefficient of the coil, and then the measurement circuit converts it into a change in voltage output, achieving the conversion of non electrical quantity into electrical quantity. When the armature is in the middle position, the two secondary windings have the same mutual inductance, so the primary side excitation obtains the same induced electromotive force.
Due to the reverse series connection of two secondary windings, the differential output electromotive force obtained is zero. Set this position as the standard position for detection, that is, when installing an inductance micrometer device, this position is detected as a standard steel ball with a diameter of 9 mm. When the diameter of the measured steel ball is greater than 9 mm, the armature will move up, so the mutual inductance of the upper secondary winding is greater than that of the lower secondary winding. The induced electromotive force in the upper secondary winding is also greater than that of the lower secondary winding. The differential output electromotive force is not zero, and each electromotive force value corresponds to a steel ball of a certain diameter, thus measuring the diameter of the steel ball. Similarly, when the diameter of the steel ball is less than 9 mm, the armature will move downwards. Therefore, the mutual inductance of the lower secondary winding is greater than that of the upper secondary winding, and the induced electromotive force in the lower secondary winding is also greater than that of the upper secondary winding. The differential output electromotive force is also not zero, and the diameter of the steel ball is measured.
2.3 Automatic sorting device
The upper surface of the receiving box device (Figure 2) has a raceway at 30 ° to the horizontal, with baffles on both sides. The steel ball rolls down the raceway by its own weight. Using a steel ball with a diameter of 9 mm as the standard, 1 μ M is divided into 8 groups with a gauge interval of -3, -2, -1, 0, 1, 2, 3 μ For m and non-conforming products, each group corresponds to a receiving box opening, and the flap of each receiving box opening is controlled by an electromagnet (on/off). When the voltage signal output by the inductance micrometer device is sent to the PLC controller, the PLC will control the corresponding electromagnetic iron to be energized and open the corresponding material box flap.
1- Electromagnet; 2- Connecting rod; 3- Material box flap; 4- Both side baffles
Figure 2 Structural diagram of the receiving box
The MQD06 series electronic traction electromagnet is selected as the electromagnet. The electromagnet is mainly composed of electromagnetic choke, armature, coil, and control electrical components. When the coil is energized, the armature is attracted, and the connecting rod drives the controlled material box flap to open; After the coil is powered off, the electromagnet itself does not have a reset device, and the flip plate falls due to its own gravity, which drives the armature to reset through the connecting rod, restoring its operation within the rated stroke.
3. PLC control system
The control system design includes two major parts: hardware and software. The electrical control system includes pneumatic system solenoid valves, limit switches, inductance micrometers, electromagnets, and various control switches.
3.1 Hardware System
Based on the workflow and working characteristics of the measurement and sorting device, the number of input and output points is estimated. According to the statistics of the controlled object, there are 21 input points and 11 output points. After considering a 10% to 20% expandable margin, the number of input and output points is rounded and determined to be 24 for each input and output point. Based on the calculation of storage capacity, it is finally determined that the PLC will be of the overall type, with a 220 V AC power supply and a total of 48 I/O points. The transistor output type will be selected. Finally, considering factors such as economy, the PLC of this device uses Mitsubishi FX2N-48MT-001. Considering the voltage signal output by the inductance sensor circuit, the analog module FX2N-2AD also needs to be selected.
3.2 Software System
Write PLC running program:
(1) Initialization program;
(2) Main program;
(3) Interrupt subroutine;
(4) Procedures for detection, fault diagnosis, and display;
(5) Protection and interlocking program.
4. Conclusion
The measurement and sorting device uses an inductance sensor to measure the diameter of steel balls with high precision, and uses an electromagnetic flipping device for accurate sorting. Combined with a PLC control system, the automation of steel ball diameter detection and sorting is achieved. The design structure is simple and reasonable, with high measurement and sorting accuracy and improved work efficiency. Based on this working principle, the detection and sorting of steel balls with different diameters can be carried out through improved design, thereby expanding the application range.
2023 New Week WBM Product Recommendation:
Steel Ball Cold Heading Tools：
In the steel ball cold heading process, after barstocks are cut into column-shaped blanks, two ends of the column shaped blanks are rubbed and cut into inversed angel or round angle shapes, and then the blanks are transferred to a cold heading mechanism to be headed into steel ball rough cast; a blank rubbing and cutting mechanism is additionally arranged on the corresponding cold heading machine. The quality and eligibility rate of the steel ball rough cast can be enhanced and the manufacturing cost thereof can be reduced. Furthermore, as the shapes of the blanks entering the cold forging mechanism are regular, the stress born by the cold heading mechanism is equal in the punching process, thus the service life of cold heading dies is prolonged.
