I. Core sources and protection logic of general mechanical hazards
1. Risk of workpiece rebound
During the machining process, the workpiece may experience unexpected rebounds (such as flying metal chips and rebounding wood blanks) under the influence of cutting forces, impact forces, or vibrations, directly hitting the exposed parts of the operator's hands, face, etc. Protection should start from the design end: improve the clamping stability of the workpiece by optimizing the fixture structure (such as adding anti - slip teeth and hydraulic clamping); set up elastic buffer components (such as polyurethane baffles) to absorb the rebound energy; install transparent protective baffles in high - speed cutting areas (such as milling machines and planers) to limit the movement trajectory of the workpiece and prevent it from being ejected onto the human body.
2. Danger of tool contact after shutdown
For some machinery (such as lathes and drill presses), after the power is cut off, the cutting tools may continue to rotate due to inertia, or the cutting tools may not be completely separated from the workpieces. If operators accidentally touch them, they are likely to be cut or entangled. Automatic stop devices need to be equipped: Use electromagnetic brakes (response time ≤ 0.5 seconds) to immediately brake the spindle after the shutdown signal is triggered; Design mechanical interlocking mechanisms (such as the cutting tools automatically retract to a safe position after shutdown) to ensure that the cutting tools are completely separated from the workpieces; Set up a "machine stopped" indicator light on the control panel to visually indicate the dangerous state.
3. Injury risks of non - fully automatic machinery with cutting tools
Manual feed or semi - automated machinery (such as table saws and hand - held grinders) lack closed - loop control. Operators need to directly contact the area near the cutting tools, which makes it easy for their hands to accidentally enter dangerous areas. Protection strategies include: using cutting tools with a circular cross - section (such as spherical milling cutters) to reduce cutting sharpness and limiting the single - pass cutting thickness (≤ the safety threshold corresponding to the material hardness); installing a two - hand start device (both hands must leave the cutting tool area during operation), or adding a contact - type safety sensor (such as a capacitive hand guard that stops the machine when it senses the approach of a hand).
4. Extrusion, shearing and entanglement hazards of moving components
The rotating shafts of machinery (such as motor shafts and gears), reciprocating mechanisms (such as crank - slider mechanisms), and transmission systems (such as belts and chains) are high - frequency hazard sources: rotating parts can easily entangle clothing and hair, reciprocating parts can easily crush fingers, and meshing parts can easily shear limbs. The core protection measure is isolation by guards: fixed guards (such as gearbox casings) cover long - term exposed hazardous areas and are fixed with bolts to prevent unauthorized disassembly; movable guards (such as guide rail guards) open and close synchronously with moving parts to ensure there are no exposed gaps throughout the process; guards must meet the opening limit of "five fingers cannot reach in" (aperture ≤ 8mm) and use anti - static materials to avoid dust accumulation affecting the field of vision.
II. Key points of safety design for sewing machine heads
1. Broken needle rebound protection
When the sewing needle pierces the fabric at a high speed (the rotation speed can reach 3000 stitches per minute), if it encounters a hard object (such as a button or a zipper) or the needle body breaks due to fatigue, the broken needle will eject at a speed of 10 - 20 m/s, which may easily injure the vulnerable parts such as the eyes and face of the operator. Double protection needs to be set up: The needle guard (made of transparent polycarbonate) covers the front and top of the needle tip's movement trajectory, with a thickness of ≥ 2mm to block the impact of the broken needle; An arc-shaped baffle is installed at the front end of the machine head to form a "U-shaped" protection area, and an observation window (with a diameter of ≤ 30mm) is reserved at the same time to ensure the visibility of the sewing material; The needle guard is connected to the machine head by a snap-on connection for easy disassembly when quickly replacing the sewing needle.
2. Design of needle tip finger guard
During sewing operations, operators need to use their fingers to push the fabric near the needle tip (distance ≤ 5mm). It is easy for the needle tip to pierce the fingers due to hand tremors. A finger guard device needs to be integrated at the throat plate: Use an elastic metal sheet (such as beryllium copper alloy), with the front end bent into a "V shape", which fits the fabric surface and moves synchronously with the sewing material. It neither affects the feeding nor physically isolates the fingers from the needle tip; The surface of the finger guard device needs to be rounded (R ≥ 0.5mm) to avoid scratching the sewing material or hands.
3. Protective cover for transmission parts
There is a risk of entanglement at the pulley of the sewing machine head (connecting the motor and the spindle) and the gear meshing area (such as the operator's cuffs or long hair getting caught). The protective cover shall meet the following requirements: Fully enclose the transmission path, leaving only the motor cooling holes (hole diameter ≤ 5mm); Adopt a detachable structure (such as hinge connection) for easy opening during maintenance; The clearance between the protective cover and the transmission parts shall be ≥ 10mm to avoid abnormal noise or wear caused by friction; Mark the "Danger of Rotation" warning sign (a triangle with a yellow background and black border) on the surface.
III. Core requirements for the safety control of injection molding machines
1. Component selection for the safety control circuit
The safety functions of the injection molding machine (such as mold closing protection and emergency stop) rely on the reliable operation of the control circuit. The components need to meet the dual standards of "maturity" and "stability":
Maturity: Priority should be given to components that have run for more than 100,000 hours without failure in the plastic machinery field (such as Omron G9SA safety relays and Schneider XPS - AC safety controllers), or products that meet the IEC 61508 SIL2 level. Avoid using new components in the experimental stage.
Environmental adaptability: It needs to withstand the high temperature (60 - 80°C), oil pollution, and vibration environment in the injection molding workshop. For example, the terminal block uses gold-plated contacts (to prevent oxidation), and the wires are selected with fluororubber insulation layers (with a temperature resistance of ≥150°C).
Circuit design measures: Isolate high - voltage electricity (motor drive) from low - voltage electricity (control signals) through optocouplers to avoid electromagnetic interference; Reserve a 20% margin for the cross - sectional area of the wires and the rated current of the terminals (for example, a terminal rated at 10A actually carries ≤ 8A); Set up dual - channel signal verification (for example, compare the signals of dual light curtain sensors, and stop the machine if the deviation
2. Machine safety stop function and stop categories in EN 60204-1
The stop function of the injection molding machine needs to select the corresponding category according to the risk level (such as clamping force, injection speed). EN 60204-1 defines three types of stop mechanisms:
Stop category 0 (immediate power cut-off stop): Cut off all power supplies for motive power (motors, hydraulic pumps), and rely on mechanical braking (such as brake pads) to stop the moving parts due to inertia. It is applicable to high-speed and dangerous actions (such as the advancement of the injection cylinder), with a response time ≤ 0.2 seconds, to prevent the mold from squeezing the operators.
Stop Category 1 (Controlled Deceleration Stop): Keep the power supply of the actuator (such as the mold - closing hydraulic valve). Control the flow rate through the proportional valve to make the components decelerate at a constant speed. Cut off the power supply after a complete stop. It is suitable for precision positioning scenarios (such as closing the mold to a 0.1mm gap) to avoid mold misalignment caused by sudden stops.
Stop Category 2 (Controlled stop with power maintained): The drive unit remains energized, and only the dangerous actions (such as stopping the injection) are halted, facilitating a quick resumption of production (such as restarting after replacing raw materials).
Selection principle for stop categories: It is necessary to base on the risk analysis results of prEN 954 - 1. All injection molding machines must have Category 0 function (as the last line of safety defense); Category 1/2 shall only be used when the functional requirements are clear (for example, Category 1 is used for mold protection, and Category 2 is used for semi - automatic production mode).
3. Two-hand control devices and safety distance protection
Two-hand control device: During high-risk operations such as mold closing and injection, operators are required to keep their hands away from the mold area through two-hand buttons (the distance between the buttons is 500 - 800 mm to prevent single-hand simultaneous operation). The device needs to meet the requirements of "synchronization" (the interval between pressing the two buttons ≤ 0.5 seconds) and "fail-safe" (releasing any button will trigger a Category 0 stop), and pass the EN ISO 13849-1 PLd level certification.
Solutions for safety distance:
Physical isolation: The safety door is equipped with a reed switch with an operating part (forced disconnection type). The mold closing cannot be started when the door is not closed.
Electrically sensitive protection: Install a Type 4 light curtain (resolution ≤ 14mm, stop immediately when occlusion is detected) or a laser scanner (scanning angle 190°, response time ≤ 20ms) at the entrance of the dangerous area.
Area protection: Lay a safety carpet in the operation area (trigger pressure: 0.5 - 5 N/cm²), covering the area 1.5 m in front of the mold.
Control circuit enhancement: Use a safety monitor module (such as Siemens 3RK3) to implement the logic control of two-hand start and safety door interlock, meeting the requirements of EN ISO 13849-1 PL e level and improving safety integrity.
I. Limitations of traditional security protection means: Dilemma of scenario adaptation
In the safety protection system of industrial equipment, safety fences and protective doors are common physical isolation solutions, but there are significant boundaries to their application. On the one hand, some scenarios cannot be adapted to physical isolation due to operational requirements. Taking large injection molding machines as an example, when the equipment is being maintained or the mold is being adjusted, operators need to enter the core internal areas of the machine (such as the clamping mechanism and the injection unit). At this time, the risk of accidental external startup must be strictly eliminated. If traditional protective doors are used, although they can trigger the equipment to stop when the door is opened, the equipment may need to remain powered off or in a specific standby state during maintenance. The mechanical structure of the protective door cannot precisely match the logic of "absolutely prohibit external startup when personnel are operating inside", and instead may pose potential hazards due to issues such as accidental door closure and signal delay.
On the other hand, even if the scene is technically compatible with the protective door, it may be discarded in practical applications due to the requirements of "convenience" and "aesthetics". For example, in workstations where frequent material loading and unloading and semi - finished product transfer are carried out, the repeated opening and closing of the protective door will reduce the operation efficiency; in intelligent workshops that focus on the smoothness of human - machine cooperation, the prominent structure of the protective door may damage the aesthetic feeling of the overall layout and even affect the path planning of automated equipment such as AGVs. These contradictions have given rise to the demand for non - physical contact and flexible protection solutions.
II. Contact-type safety protection devices: The core role in filling the gap
Facing the limitations of traditional protection methods, contact-type safety protection devices have become a key alternative solution due to their characteristics of "no physical isolation" and "dynamic response". Such devices trigger safety signals by sensing human contact or entry into the action area, and can achieve protection of dangerous areas without a rigid structure. Safety carpets are a typical representative with mature technology and wide applications among them.
The core principle of the safety carpet is based on pressure sensing technology: Its surface is made of durable elastic materials (such as rubber and polyurethane), and an array of pressure sensors is embedded inside. When it is stepped on by a certain weight (usually with a preset trigger threshold, such as over 50 kg), the sensors output digital or analog signals in real - time, which are then connected to the equipment control system through a safety relay. After the system receives the signal, it immediately executes the preset safety actions (such as stopping the machine, cutting off the power source, locking the starting circuit) until the triggering condition is removed (the person leaves the carpet area). This "stop when a person enters" response mechanism perfectly solves the core risk of "external startup when a person enters a dangerous area".
III. Technical Features and Application Advantages of Safety Mats
Compared with solutions such as protective doors and light curtains, the uniqueness of safety carpets is reflected in three aspects:
1. Spatial adaptability and scene flexibility
Safety carpets can be custom - cut according to the shape and size of the dangerous area. They can be laid on the ground or the surface of the equipment platform without occupying vertical space. They are especially suitable for irregular areas (such as equipment corners and the edges of operating consoles) or the protection areas that need to be temporarily expanded. For example, in a robotic welding workstation, a circular safety carpet can be laid around the movement trajectory of the robotic arm. Once a person steps on it, the machine will stop immediately, eliminating the need to set up fences that may block the surrounding material turnover passages.
2. Seamless operation and efficiency improvement
Traditional protective doors need to be manually opened and closed. Frequent operation may cause personnel to find it troublesome and illegally short - circuit them; light curtains may be falsely triggered due to dust or workpiece occlusion. The safety carpet is triggered by "natural stepping" without additional operations, which not only avoids loopholes caused by human intervention but also does not affect the normal operation process. At the chassis assembly station of the automobile general assembly line, when workers stand on the safety carpet to operate, the carpet remains in the triggered state, ensuring that the robot suspends its operation; after completion, when workers leave the carpet, the robot automatically resumes operation, achieving seamless connection of "safety when people are present, and start - up when people leave".
3. Environmental tolerance and durability
Industrial scenarios have strict requirements for equipment reliability. Safety carpets meet this demand through material and structural design: The surface is made of rubber material that is wear-resistant, oil-resistant, and acid-alkali-resistant, which can withstand forklift rolling and tool impacts. The internal sensors are sealed to adapt to the high-temperature (-30°C~80°C), humid, and dusty environment in the workshop. Some high-end models also have an IP67/IP68 protection rating and can be directly used in food and pharmaceutical workshops with frequent cleaning. Their mean time between failures (MTBF) can reach over 100,000 hours, reducing maintenance costs.
IV. Typical Application Scenarios and Value Realization
The application of safety carpets has penetrated into various types of industrial scenarios. Its core value lies in the dual realization of "risk prediction" and "process optimization".
High-risk equipment maintenance scenario: In the mold replacement areas of large stamping presses and die-casting machines, safety carpets are laid at the entrances. Once maintenance personnel step on them, the equipment's startup permission is locked, preventing mechanical injuries caused by others accidentally pressing the startup button.
Human-machine collaboration workstation: An assembly line where collaborative robots and humans operate together. Carpets are laid in the manual operation area. When a person enters, the robot slows down or stops, and resumes high-speed operation after the person leaves, balancing efficiency and safety.
Frequent access area: The manual picking station of the logistics sorting line. Workers frequently cross the conveyor belt. When the carpet is triggered, the conveyor belt pauses to avoid the risk of pinching, and at the same time, it saves the waiting time for opening and closing the protective door.
Through the implementation of these scenarios, safety carpets not only address the pain point of "physical barrier" in traditional protection methods, but also promote the upgrade of industrial safety from "passive protection" to "active early warning" with their flexible and intelligent features, becoming an indispensable part of the safety system in modern factories.