One of the main advantages of AGVs is that they do not damage people or infrastructure. This is indeed the case, AGV is safer than traditional manual vehicles such as traditional forklifts.
In order to make the AGV system safe, the AGV must comply with some safety rules or safety standards. In order to meet these safety standards, AGV must include some safety sensors and equipment to avoid or prevent risks.
What is the AGV safety standard?
The American AGV safety standard is determined by ANSI B56.5-2012 "Unmanned, Automatically Guided Industrial Vehicle Safety Standard" and manned industrial vehicle automation functional standards.
The European AGV safety standard is EN1525: 1997 "Safety of Industrial Trucks-Unmanned Trucks and Their Systems". Both specify safety requirements related to the design, operation and maintenance of autonomous vehicles. The following are some key elements:
Vehicle safety and emergency controls and devices
Vehicle safety and emergency control devices refer to devices that automatically and quickly stop propulsion, stop moving parts, and brake. The agv should include sensors that cover the maximum movement width and / or length to prevent contact between the load and any obstacles.
The response time of the braking system, the object detection system and the safety control system will cause the vehicle to stop, affect the structure between the vehicle and other installation equipment, including its expected load, and the obstacles will be felt in advance of the main development direction of the moving vehicle.
Travel that deviates from the intended route should require emergency parking.
AGV Security System
The safety elements of automatic guided vehicles can be divided into two major categories: active safety elements and passive safety elements
The main AGV active safety devices are:
AGV safety laser scanner or AGV collision avoidance system
Contact buffer for stopping AGV
Emergency stop button
The most important passive safety devices are:
Audible warning / alarm signal
Signs on AGV vehicles
AGV safety laser scanner or AGV collision avoidance system-active AGV safety system
If it is used as the main sensing device, this non-contact sensing device (s) should be operated and installed in it, an automatic fail-safe device, when sensing the path distance of people or objects in the vehicle is not less than the frontier direction of the sensing field The main movement will cause the vehicle to contact the vehicle structure and people or objects before it stops safely.
At present, "safety laser" is the king of AGV safety system. There are several brands of safety lasers on the market, but they all work similarly.
There are at least two safety areas for safety lasers used in the AGV industry.
The first is the "warning field". When the laser detects an obstacle in the field, the AGV decelerates.
The second and most important one is the "safe area" or "protected area". If the laser detects certain elements in this field, the AGV will stop. This is the only area that contributes to AGV safety certification.
Both the warning and safety fields define "safe areas".
The design of the safety zone must be based on many factors, such as the surrounding area, vehicle speed, payload, and floor conditions. Each waypoint passed by the AGV must have its own safety zone to ensure that the time and distance at which the vehicle stops will avoid any contact with obstacles.
The time (and distance) required to stop an AGV with a load of 1,000 kg at 2 m / s is completely different from the time (and distance) required to stop an AGV with a load of 200 kg at 1 m / s. The inertia involved in these two cases is completely different.
Of course, in the first case, you will need a longer area of safety inspection in order to allow the AGV to stop in time before touching the obstacle. The AGV will continue to run automatically after the obstacle is removed from the "safe" area for about three seconds. It automatically rearms.
Parking distance should also consider other factors, such as ground roughness, slope, sliding surface, etc.
AGV will continuously change its safety map while driving. The arrangement of the safety zone must be completed by a skilled technician at the end of the installation phase. The safety zone is designed directly in the laser assembly by software / tools provided by the laser manufacturer . The safety system management must be independent of the AGV management system.
As pointed out, the safety map must also adapt to the surrounding environment. In some cases, the safety map must be modified because some elements in the route cannot be deleted and should be "ignored" to allow the AGV to continue driving. Of course, in this case, the speed and operation of the AGV must be programmed accordingly in accordance with safety standards.
Suppose you have an AGC, an automatic guided car, which must pass under the car to connect with a pin hook. In this case, the AGC must adapt the safety zone to a very narrow and small one, otherwise the safety zone will "see" the cart wheel and recognize it as an obstacle, preventing AGV. Although the safe area is small, the AGV speed must be low. Once the AGV is engaged with the car and the safety area is out of the car (so no "seeing" wheels), the AGV can accelerate, so the safety area must be expanded.
How does AGV adjust the safety map at each point of the route?
A safety laser can store a certain number of maps, and a laser scanner allows 4 maps and 32 or more safety scanners.
The AGV management system can indicate to the AGV which safety maps must be used. This information can be provided by coordinates, mainly in lgv and agv, under the guidance of free navigation (slam or lider, ecc), for example, use map 2 in coordinates X = 5 / Y = 23.
Magnetic, wire, and optically guided AGVs use labels or transponders located on the ground to indicate what map the AGV uses. For example, use map 4 in trasponder 5634.
If you want to know more about the different navigation systems available for AGV, please check this article: Types of AGV Navigation System Automated Navigation Vehicles
Major AGV safety laser supplier
The main autopilot safety laser manufacturers are:
Contact buffer for stopping AGV-active AGV safety system
The AGV does not need to be covered by a 360 ° safety laser to avoid collisions. The safety laser is used to cover the running direction of the agv when it reaches the relevant speed. If the AGV runs fast, it must stop before it encounters anything.
Safety scanners are not cheap (about $ 2,500 per unit), their integration in AGV systems can increase the price, due to precise programming, integration in safety PLCs, etc. Many avvs have safety bumpers installed on the parts or edges that are not covered by the laser. The size of the buffer depends on the force exerted on the obstacle. The principle is simple. If the AGV encounters a person, it will not be injured.
ANSI B56.5 stipulates: "If used as an object sensing device, the bumper should be safe during operation and installation, and no force greater than 134 N that is parallel to the ground and opposite to the direction of the bumper should be applied." Start of the bumper Should be within the foldable range of the bumper (ie, before the vehicle structure contacts) ".
The only way to avoid injury is to touch at low speed. For this reason, the bumper is located in the AGV area and may be exposed to something at very low speed. Both en1525 and ANSI B56.5 indicate that the speed is lower than 0,3 m / s (18 m / min), no collision avoidance system is needed (thus no laser), but there must be a clear audible and visual alarm signal.
Emergency stop button-Active AGV safety system, each AGV has an emergency stop button.
The number and position of emergency stop buttons are determined by the shape and size of the AGV.
The emergency button must be visible, distinguishable, and easy to reach the AGV from either side. No matter what happens, the operator must be able to access the emergency button located on the AGV.
When the emergency button is activated, the AGV enters the emergency stop state and all movements will stop until the stop button is rearmed.
AGV safety PLC or relay
All the above-mentioned safety elements must be managed by safety PLCs or relays. Safety PLCs or relays manage all equipment and ensure safety classification. Its main function is to ensure that the vehicle stops at any time.
Warning Light-Passive AGV Safety System
The AGV is used to set a warning light. When the AGV approaches a turn, the turn light indicates that the AGV is about to turn, and reminds the personnel in the area where the AGV is located to branch left or right on the guidance path.
The AGV installs other types of optical signals to indicate several AGV states, stopped by the safety scanner, AGV running, AGV problems, ecc. The agv must be visible in any direction.
Audible warning / alarm signal-passive AGV safety system
Use different tones, songs or melody during vehicle operation, including confirmation sound and alarm sound. The AGV emits different tones during normal operation to indicate several AGV states. When the alarm is active, the alarm sounds.
Before starting the vehicle movement or remotely reactivating from the dormant or inactive state, a warning device (turning the vehicle on or off) should be activated to make it audible, visible or combined to indicate that the vehicle under automatic control is about to start. Warning lights, such as flashing lights or flashes, should be visible at all times. Vehicles should provide warning instructions with sound, vision or a combination of all vehicles during driving
Logo-Passive AGV Safety System
The AGV must have signs and symbols that indicate hazardous areas. All vehicle signs should comply with local regulations and should be durable.
Complete AGV system security
Before that, I have given some details about the AGV vehicle's own safety system. But how safe is the entire AGV project?
When installing the AGV system, the AGV supplier should follow some "rules". In any case, in some cases it is not possible to complete all safety specifications, so every AGV project should have a "residual risk assessment" between the supplier and the user.
Here are the main rules:
The minimum gap between the obstacle and the vehicle (including the load) should be maintained at 0.5 meters (19.7 inches). All other areas with reduced clearance should be considered as hazardous areas or restricted areas and clearly marked with signs, stripes, lights or other signs.
During the design, installation, and start-up phases, users and system suppliers should designate hazardous areas and / or restricted areas, and then users are responsible for clearly marking these areas with stripes, lights, or other signs. Avoid confusion with other marks and signs.
Areas with a clearance height of less than 0.5 m to 2.1 m may pose a danger to personnel. Before entering the area, the vehicle speed should be reduced and an audible warning should be issued. If the pedestrian has an escape route, the maximum travel speed should be limited to 0.3 m / s, and the vehicle path should be regarded as a danger zone.
If the pedestrian has no escape route, the vehicle path should be regarded as a restricted area. Users and system vendors should agree on appropriate protective measures for this situation. If an emergency stop device can be installed, it should be installed on a vehicle within 600 mm that the driver can reach. If the emergency stop device cannot be reached (such as a forklift storing goods in reverse), the user should be given verifiable training.
Note: The article is an independent view of the author and does not represent Soo56's position