Abstract: This paper designs a speed measurement device for a robotic arm in an integrated circuit chip testing equipment. The design considers factors such as vibration during the robotic arm's movement, and instability in speed and stroke caused by cylinder shaft aging and end rust. Precise adjustments to the device based on measurement and control parameters cleverly solve the chip failure problem caused by poor control of the robotic arm's speed and stroke, effectively reducing the chip scrap rate. 1 Introduction In today's world, chip packaging sizes are getting smaller and smaller, and nanochip manufacturing technology has become the mainstream in the chip manufacturing industry. The increasing development of manufacturing processes has increased the difficulty of processing and testing, making the analysis and testing of chip failure problems particularly important during large-scale chip production. The speed measuring instrument designed by the authors is mainly used in the Advantest M6751/T5375 testing equipment. The speed measuring instrument consists of two parts: a robotic arm for gripping chips and placing (removing) them into a dedicated test chamber; and a testing machine for testing chip functionality. Since the testing machine can test up to 32 ICs in parallel at a time, the robotic arm must be able to grip and place chips at the fastest possible speed. The Advantest M6751 robotic arm assembly includes four small suction heads, each capable of independent ascent and descent, driven by a miniature SMC cylinder. After each of the four suction heads picks up and places chips eight times, loading 32 ICs, the entire assembly then moves in the X and r directions. Due to the high testing speed requirements, the speed of the four driving cylinders had to be adjusted to be as fast as possible. However, excessive speed could damage the chips, especially thin silicon wafers in VFBGA packages, where high-speed gripping could easily destroy them, causing serious quality problems. Therefore, the cylinder speed had to be increased while ensuring quality. 2. Basic Introduction to the Test Unit The Advantest M6751A/6751AD test equipment is developed based on the M6741A. It features a new control unit to improve throughput, making it a high-capacity memory test unit capable of testing up to 4500 devices per hour. A touchscreen enhances the user interface. It uses Win95 and later versions, allowing for open system configuration based on SEMI's standard protocols, and is widely used in IC testing. However, the M6751 lacks a built-in speed testing function. The author designed a speed measurement device to enable the mechanical gripper of this equipment to have speed control functionality. 2.1 Robotic Arm Figure 1: Advantest M6751 Series Robotic Arm The Advantest M6751 series robotic arm is used in conjunction with the test unit. It is suitable for chips in various package types, from older TSOP and uBGA packages to the currently popular vfBGA and SCSP packages. The internal components of the robotic arm are divided into three parts: tray transfer, chip transfer, and test transfer. As shown in Figure 1, the left side shows the loading robot, and the right side shows the unloading robot; both operate on the same mechanical principle. The operation of the robotic gripper is as follows: The motor is the driving source for the robotic gripper. The system sends commands to the drive circuit, which then controls the cylinder to move downwards. The vacuum generator creates a vacuum to pick up the chip, and commands the cylinder to move upwards from the material tray position to the test tray position. Commands are then sent to control the cylinder to move downwards again, releasing the vacuum while blowing air to flatten the chip in the test tray. Finally, the cylinder moves upwards back to its initial position, completing the chip transfer from the material tray to the test tray. If the cylinder moves too fast during operation, it may cause the robotic gripper to vibrate, changing the position of the chip held on it. It may also cause the chip to be placed at an angle when placed on the test tray. This can have two consequences for the subsequent testing process: poor contact, making testing impossible; or the chip being broken when pressed and fixed on the testing machine. Similarly, the vibration of the robotic arm can cause the chip to shift when placed on the tray. When multiple trays are stacked together, chips not placed in the tray's positioning slot are easily crushed or have their solder balls damaged, resulting in defective products. Furthermore, the SMC cylinder shaft of the M6751 robotic arm uses 45# steel, which is prone to aging and rusting at the ends with long-term use, causing unstable movement speed and potentially leading to chip failure. Figure 2 shows a schematic diagram of the robotic arm's four suction heads and their drives; the stroke is approximately 12mm. The cylinder drive shaft moves up and down, driving the trapezoidal vacuum nozzle made of rubber with excellent sealing to move up and down. The speedometer designed in this project can accurately measure the up-and-down movement speed and stroke of the robotic gripper, and make electrical and mechanical adjustments to the cylinder's movement speed and stroke based on the measurement results, controlling the speed and stroke of the robotic gripper. 2.2 Testing Machine Figure 2: Schematic diagram of the four suction heads of the M6751 and their drives The testing machine consists of a workstation, a computer host, test heads, and an IC finished product testing interface board. It can test the performance of chip products under different temperature conditions and ensure that each chip meets its functional parameter requirements. Components are placed in the appropriate unloading area according to the test results. The workstation controls all system functions, downloads test programs, and obtains test results; the computer host contains the test circuit motherboard and necessary power supply; the test head contains electronic pin plugs for contacting chips, testing, and distributing motherboard signals to each chip pin; the IC finished product test interface board is the connection part between the motherboard, test head, and chip. [b]3 Circuit Design of Mechanical Gripper Speed ​​Meter 3.1 Circuit Structure Diagram[/b][align=center] The circuit principle block diagram of the speed meter is shown in Figure 3, and its signal pickup circuit principle is shown in Figure 4. [/align] Figure 4 Basic Principle Diagram of Signal Pickup The speed measuring device works based on Faraday's principle of electromagnetic induction. When the N pole of the magnet moves towards the coil, the magnetic flux through the coil increases, generating an induced current. The magnetic field it generates opposes the increase in magnetic flux within the coil, and the direction of the magnetic induction generated by the induced current in the coil is opposite to the direction of the magnetic field of the magnet. This current signal is converted into a voltage signal through a sampling resistor, amplified by an amplifier, and then compared with the comparator's reference voltage signal. The comparator outputs a "1", and the microcontroller starts counting. The value displayed per unit time indirectly indicates the speed at which the suction head moves downwards. When the mechanical gripper is not moving, the magnet stops moving, the coil has no induced current change, the comparator outputs a "0", and the microcontroller stops counting. (See Figure 4). When the N pole of the magnet moves away from the coil, the magnetic flux through the coil decreases, and the magnetic field of the induced current is in the same direction as the magnetic field of the magnet. A negative induced current is generated in the coil, which is the same effect as the S pole moving downwards. Therefore, to test the speed at which the suction head moves upwards, simply place the S pole downwards. When the suction head rises, a negative induced current is generated in the coil, which, after amplification and comparison, also outputs a "1", and the microcontroller counts. The value displayed per unit time indicates the speed or travel distance of the mechanical gripper. After the suction head completes one movement and stops, the counter automatically resets to wait for the next test. This design also considers the correction method for unstable measurement values ​​caused by the micro-vibration of the magnetic sheet during movement when programming the microcontroller. The cylinder pressure of the mechanical gripper is adjusted according to the counting display results to obtain precise speed and stroke control. 3.2 Circuit Schematic and Introduction of Each Unit The schematic diagram of the speed measuring circuit with AT89C2051 as the main control core is shown in Figure 5. [b]3.2.1 Power Supply Circuit[/b] The speed measuring device is powered by a 9V dry cell battery. The +5V in the circuit is output by the three-terminal voltage regulator IC 7805 as the main power supply, and the -5V auxiliary power supply is composed of ICL7660. They are simultaneously connected to pins 8 and 4 of the precision operational amplifier OP77, which uses a dual power supply. OP77 constitutes an inverting input amplifier. The load current of 7805 reaches about 350mA, and the power consumption is relatively low, so no heat sink is required. The -5V power supply is output by the ICL7660. The ICL7660 operates within a voltage range of +1.5V to 10.5V, providing 10-20mA of current to the load. Its own power consumption is less than 0.5mA when connected to a load, and its conversion efficiency is over 95%. The external circuit requires only two external capacitors to operate. It can withstand continuous short circuits when the power supply voltage is less than 5.5V. It utilizes an oscillator and a multiplexer to achieve voltage polarity reversal, making it a variable polarity DC-DC converter that can convert a positive voltage input to a negative voltage output, i.e., Ui and Uo have opposite polarities. Pin 1 is unused; pins 2 and 4 are connected to the positive and negative terminals of a 10μF/26V electrolytic capacitor, respectively; pin 3 is signal ground; pin 5 is the negative voltage output terminal, connected to ground with a 10μF/26V electrolytic capacitor C2; pin 6 is the low-voltage terminal of the chip's built-in power supply. When Ucc > 3.5V, this terminal is open; when Ucc < 3.5V, this terminal should be grounded to improve the low-voltage operation performance of the circuit; pin 7 is the external capacitor or clock output terminal for the oscillator. Without a capacitor, the oscillation frequency is 10kHz. If it is necessary to reduce the oscillation frequency, an external capacitor C should be connected. When C = 100pF, f ≈ 1kHz; when C = 1000pF, f ≈ 100Hz. The oscillation signal can also be taken out from this terminal; pin 8 is the positive power input terminal (1.5～10.5V), and the circuit is connected to +5V. In the circuit, C5 and C6 are both 10μF energy storage capacitors used to form a DC-DC charge pump, improving power conversion efficiency. When Ucc < +6.5V, pin 5 can be directly used as the output; when Ucc > +6.5V, to avoid chip damage, a diode VD must be connected in series in the output circuit. Capacitor C7 is a bypass capacitor connected between the input power supply and ground to enhance anti-interference capability. The -5V power supply is an auxiliary power supply, and the power consumption of the subsequent load OP77 is also relatively low. Using ICL7660 to build the -5V circuit can meet the design requirements. 3.2.2 Signal Conditioning Circuit The current signal induced on the coil is converted into voltage through resistors and capacitors. Generally, the induced signal is very weak, requiring OP77 to amplify it to about 200 times before sending it to comparator LM393 for comparison with the reference voltage signal, and then sending the output level to the microcontroller. The OP77 is an ultra-low offset voltage operational amplifier with high gain, low power consumption, low initial Uos drift, and fast settling time. It eliminates nonlinear errors in the preamplifier circuit, making it ideal for high-resolution instruments and electronic systems with stringent error requirements. The dual-supply inverting input amplifier effectively improves accuracy, and its full-scale output is ±5V. A 2.4kΩ input resistor R1 is connected to pin 2 of the inverting input, and a 2.4kΩ external resistor R2 is connected to pin 3 of the non-inverting input. A 500kΩ feedback resistor R3 is connected between pins 2 and 6. Pin 4 is connected to -5V, and pin 7 is connected to +5V. Pins 1, 5, and 8 are left floating. The amplifier's voltage gain is -(R3/R1) = -(500kΩ/2.4kΩ) = -200. The LM393 op-amp is used as a comparator; an adjustable potentiometer R5 is connected to its negative terminal to stabilize the output. As the principle of electromagnetic induction states, an induced current is generated in the coil only when there is relative motion between the magnet and the coil. The greater the relative speed, the greater the induced current. The initial speed of the magnetic strip is slower than its steady-state speed, resulting in different induced currents. These different currents, after amplification, produce different output voltages. However, what is actually needed to measure is the steady-state speed. This can be achieved by adjusting the voltage at the comparator's comparison terminal to set a low voltage. This removes the voltage caused by the unstable movement of the magnetic strip during comparison, thus achieving noise reduction. Choosing an adjustable reference voltage allows for adjustment based on different operating conditions and environmental interference, reducing measurement errors. The LM393's output pin is an open-collector (OC) gate, requiring a pull-up resistor. In this circuit, it is connected to P1.2 of the AT89C2051. Since the AT89C2051 has internal pull-ups from P1.2 to P1.7, the pull-up resistor at the LM393 output terminal is omitted in the circuit. 3.2.3 AT89C2051 Main Control Circuit and Peripheral Circuits The main control chip for the speed measuring device is the Atmel AT89C2051, a low-voltage, high-performance CMOS 8-bit microcontroller. It contains 2k bytes of erasable and rewritable read-only memory (PEROM) and 128 bytes of random access memory (RAM). Manufactured using Atmel's high-density, non-volatile memory technology, it is compatible with the standard MCS-51 instruction set. The chip integrates a general-purpose 8-bit central processing unit and Flash memory, offering powerful functionality. The crystal oscillator circuit uses a 6M quartz crystal and two 30pF start-up capacitors, connected across a 1MΩ resistor to prevent oscillation interruption. P1.2 is connected to the output of the comparator LM393 to determine if P1.2 is triggered; if triggered, counting begins. The counting standard is 1ms, and the designed range is 999ms. Three digital tubes display the hundreds, tens, and units digits respectively. The MCU program is written using a WH200 programmer/encryptor. Due to space limitations, details are omitted here. The watchdog circuit functions as both a monitor and actuator, aiming to improve the reliability of the measurement and control system. The circuit uses a 14-bit binary serial oscillator/frequency divider oscillator CD4060 to implement the hardware watchdog circuit, which has a wide voltage range (3-15V). With R1=130kΩ and C1=100pF, the oscillation frequency, after internal 14-stage frequency division, is approximately 2Hz at pin 3. R2 is the bias resistor. Under normal circumstances, the AT89C2051 resets the CD4060 every time interval t1. If the CPU malfunctions for some reason, the CD4060 cannot be reset in time. After time t2 (t2>t1), a high level is output from pin 3 to reset the AT89C2051, returning the CPU to normal operation. Then, the CPU resets the CD4060, restoring pin 3 to a low level. R3 and C2 form a differentiating circuit, which converts the reset level output from port P3.4 into a reset pulse. GAL16V8D Decoding and Driving Circuit. GAL (Generic Array Logic) is a large-scale application-specific digital integrated circuit manufactured using advanced E2PROM technology. GAL devices are characterized by high speed, low power consumption, user-programmable nature, and flexible structure. The logic function of the GAL's input buffer is to convert the output variable into its original and inverse variables, providing input signals for the AND gate array. Simultaneously, due to the high input impedance of CMOS technology, the required input drive current is significantly lower than that of common bipolar devices, resulting in a high fan-out coefficient for the driving circuit. It is also compatible with TTL circuits and can directly drive digital tubes. The GAL16V8D decodes and drives the digital tube display, with the number of digits controlled by a microcontroller. The microcontroller's P1.7 is connected to the enable pin 12 of the GAL16V8D, P1.6 to pin 9, and P1.5 to pin 8, correspondingly displaying the hundreds, tens, and units digits. In the circuit, the GAL16V8D operates in normal mode and has four input terminals, each connected to the microcontroller's output. Pin 2 of the GAL16V8D corresponds to P3.0 of the microcontroller; pin 3 corresponds to P3.1; pin 4 corresponds to P3.2; and pin 5 corresponds to P3.3. It has seven output terminals connected to the pins of the digital display. The GAL16V8D decodes a 4-bit binary number. The GAL16V8D is programmed using ABEL language to implement the decoding function; the GAL program is briefly described below. The digital display circuit uses the SP402401 LED digital tube from Ouxing Electronics, with a voltage range of 1.8–2.3V. It features red color, high brightness, low power consumption, and low price. The SP402401 uses a common cathode connection, with a drive current between 5 and 10mA. After decoding, the GAL16V8D drives the SP402401 LED digital tube. Pins 8, 9, and 12 of the SP402401 are chip select enable pins, and pin 3 is the decimal point. Pin 1 corresponds to segment E of the digital display, pin 2 to D, pin 4 to C, pin 5 to G, pin 7 to B, pin 10 to F, pin 11 to A, and pin 6 is left floating. [b]4. Use of the Speed ​​Meter 4.1 Circuit Signal Flow[/b] When the magnet moves, the change in the magnetic field will induce a current in coil L. This current is connected to pin 2 of the OP77's inverting input via resistor R1, amplified 200 times, and output at pin 6. The output voltage is then coupled to pin 3 of the LM393's non-inverting input via resistor R4. This voltage is compared with the reference voltage on the adjustable potentiometer at the inverting input, and the output level is displayed at pin 1. The output level on pin 1 of the LM393 is connected to P1.2 of the AT89C2051. If P1.2 receives a high level, the microcontroller triggers counting with a timing step of 1ms until P1.2 receives a low level to stop counting. Simultaneously, the count value is sent to the display buffer. Decoding is performed jointly by the AT89C2051 and GAL16V8D. The decoding inputs are pins P3.0, P3.1, P3.2, and P3.3 of the microcontroller, and the outputs are pins 13 to 19 of the GAL16V8D, corresponding to the seven-segment display. Pins P1.7, P1.6, and P1.5 of the microcontroller control the digital display output. [b]4.2 Adjustment of the Speed ​​Meter[/b] The tester does not require additional installation of the original equipment; it only utilizes the vacuum function built into the robotic arm. In practical applications, simply evacuate the vacuum suction head to pick up a magnet, align the coil sensor of the tachometer with the magnet, and then mechanically control the up-and-down movement of the vacuum suction head. The instrument can measure the downward or upward speed based on the N and S poles of the magnet, respectively. The movement speed of the mechanical gripper is displayed on an LED. The method for controlling the movement stroke of the mechanical gripper is shown in Figure 6. The cylinder drives the up-and-down movement of the suction head. The standard maintenance specifications for the equipment stipulate that when the cylinder is in its initial state, the contact range between the connecting block of the suction head and the top of the cylinder linkage shaft must be between 0.5 and 1 mm (measuring with a feeler gauge). When the suction head moves downward, a white hard plastic stop is used to block and control it, preventing the suction head from moving too far downward. Another function of the white hard plastic stop is to buffer the vibration caused by the movement of the suction head. The movement distance of the suction head is limited, typically with a stroke of 12 mm. Figure 6: Schematic diagram of tachometer usage Mechanical gripper movement speed control. The suction head is driven by a cylinder. By controlling the speed of the cylinder, the downward speed of the suction head can be controlled. The change in cylinder speed is caused by the flow rate entering the cylinder. Therefore, by mechanically adjusting the flow rate into the cylinder, the cylinder speed can be changed, achieving the purpose of speed control. 5. Conclusion Speed ​​measuring devices are mainly used for speed testing of short-distance moving parts. Through operation and use in actual testing processes on the production line, they can achieve relatively accurate measurement and control of the movement speed of the mechanical gripper of chip testing equipment. This improves testing efficiency and yield without affecting chip testing quality, shortens the testing cycle, and reduces testing costs.