The shock absorption and ground adaptability of an AGV mainly depend on its suspension and floating drive unit structure, together with the springs and damping components used in the assembly. This arrangement allows the drive unit to move vertically relative to the chassis, helping the wheels follow uneven floor surfaces while maintaining sufficient ground contact force and traction.
In multi-wheel AGV chassis designs, rigidly mounting the drive wheels and support wheels can cause some wheels to lose contact with the floor when the vehicle passes over depressions or raised areas. This may reduce traction and result in uneven load distribution. A floating structure addresses this problem by allowing the drive unit a certain degree of vertical movement.
Springs and dampers perform different functions. A spring provides elastic support and restoring force while storing elastic potential energy as it deforms. A damper dissipates energy through hydraulic resistance, friction, or other damping mechanisms to reduce continued oscillation. Some AGVs use a spring-loaded floating mechanism without a separate hydraulic shock absorber.
1. Common Floating Suspension Structures in AGVs
Depending on how the drive unit connects to the chassis, common AGV floating suspension designs include pivoted swing-arm structures, vertical guide-post structures, scissor-linkage structures, oscillating axle structures, and four-bar linkage structures. These designs differ in their movement, installation space, load capacity, and ability to accommodate uneven floors.
1. Pivoted Swing-Arm Structure
The pivoted swing-arm structure is commonly used in AGV drive units. In this arrangement, the drive wheel, motor, and associated transmission components form a single drive module. The module connects to the vehicle chassis through a pivot joint, allowing it to swing vertically around the pivot point.
A compression spring or another elastic element is installed between the drive module and chassis to provide preload and restoring torque. When the drive wheel encounters a raised section of the floor, the drive module pivots upward and compresses the spring. When the wheel passes over a depression, the restoring force helps push the drive wheel downward to maintain contact with the floor.
This arrangement uses the lever geometry of the swing arm to adjust the ground contact force of the drive wheel. Because the pivot location, spring mounting position, and wheel contact point have different geometric relationships, spring compression and drive wheel travel are not necessarily proportional.
Pivoted swing-arm structures are suitable for AGVs that require a combination of load capacity and ground adaptability, particularly when sufficient installation space is available. The design must also account for changes in loading under different travel directions and on sloped surfaces. The strength of the pivot shaft, swing arm, and connecting structures should be checked accordingly.
2. Vertical Guide-Post Structure
A vertical guide-post structure uses guide posts and guide bushings to form a linear motion assembly, allowing the drive unit to move vertically. The drive wheel and motor are generally mounted on a movable support plate, with compression springs installed between the movable assembly and the chassis mounting plate.
When the drive wheel encounters a raised area, the support plate moves upward along the guide posts and compresses the springs. When the wheel passes over a depression, the springs release part of their stored elastic energy. The restoring force pushes the drive unit downward.
This structure has a clearly defined direction of movement, a relatively simple mechanical arrangement, and a compact layout. It is suitable for light and medium-duty AGVs with limited chassis height or internal installation space.
However, vertical guide-post structures require accurate positioning and proper fitting between the guide posts and bushings. If the guide mechanism is significantly offset from the drive wheel contact point, additional lateral forces may develop during movement. This can cause guide-post jamming or abnormal wear. The number, position, and guiding length of the posts should therefore be properly designed.
3. Scissor-Linkage Structure
The scissor-linkage structure uses the operating principle of a scissor mechanism. Crossed connecting links join the upper and lower support frames, allowing the drive unit to move vertically within a defined range.
Springs are usually installed at suitable positions between the support frames or within the linkage assembly. When an external impact acts on the drive wheel, the scissor links move and compress or release the springs, allowing the drive unit to float.
This arrangement can combine vertical suspension movement with the installation space available for other mechanical components. It offers some space-saving advantages in integrated differential drive modules. Steering mechanisms and related connecting components can also be positioned at the sides of the scissor assembly, depending on the design.
The design must account for the movement path of the links, loads at the pivot joints, and available floating travel. Changes in linkage angle affect the force transmission characteristics, so the output support force and displacement do not necessarily maintain a constant ratio.
The ability of a scissor linkage to accommodate different floor heights on the left and right sides also depends on its specific configuration. Without an independent inclination compensation mechanism, different ground heights under the two drive wheels may cause uneven loading across the chassis. This structure is therefore better suited to drive modules designed for specific applications rather than all types of uneven terrain.
4. Oscillating Axle Structure
An oscillating axle structure connects two wheels to a common rigid axle or bridge. The center of the axle is connected to the AGV chassis through a pivot joint, allowing the complete axle assembly to rotate around this central point.
When the two wheels encounter different floor heights, the axle rotates around the central pivot. This allows each wheel to accommodate changes in ground level and helps maintain contact with the floor.
The main function of this structure is to improve ground adaptability by allowing the entire axle to pivot. In six-wheel or other multi-wheel chassis layouts, multiple oscillating axle assemblies can be arranged to accommodate local variations in floor height.
Unlike the other structures described above, an oscillating axle does not always require an additional spring. When the main purpose is to compensate for differences in ground height, the central pivot can provide the required degree of movement on its own. Springs or dampers can be added when the design also needs to control impact, adjust wheel preload, or limit axle movement.
The mechanical arrangement is relatively straightforward and is suitable for multi-wheel AGVs carrying heavy loads or operating on floors with changing surface levels. Its limitations include the need for sufficient mounting height and lateral space. The axle and central pivot must also withstand the required loads.
5. Four-Bar Linkage Structure
A four-bar linkage structure generally uses a parallelogram arrangement to connect the chassis and drive unit through four pivot joints. This allows the drive unit to move vertically within a defined range while maintaining its mounting orientation as much as possible.
When springs are incorporated into the linkage, a raised floor section causes the links to move and compress the springs. When the wheel passes over a depression, the restoring force of the springs pushes the drive unit downward to maintain ground contact.
Compared with a single-pivot swing-arm structure, a four-bar linkage provides better control over changes in the drive unit's orientation during vertical movement. With a suitable mechanical layout, it can also help control additional moments acting on the drive unit.
This structure is used in some equipment that requires the drive wheel to maintain a controlled orientation and mounting position, including certain vertical steering drive units and heavy-duty AGV drive modules.
Its main limitations are the greater number of links, pivot shafts, and mounting components. It also requires more attention to structural design and assembly accuracy, and generally occupies more space than a simple vertical guide-post arrangement.
2. Main Functions of AGV Floating Suspension Structures
A floating suspension system does more than reduce vehicle vibration. It also helps maintain drive wheel contact, distribute loads, and keep the drive unit operating within its intended range.
1. Maintaining Contact Between Multiple Wheels and the Floor
In a multi-wheel AGV chassis, the drive wheels need sufficient ground contact force to generate the required traction. If the drive wheels are mounted lower than the auxiliary wheels to ensure continuous contact with the floor, they may carry an excessive proportion of the vehicle weight. The auxiliary wheels may then have insufficient contact with the floor.
This can concentrate the load on the drive unit, increasing stress on the drive wheels, bearings, and mounting structure. It may also affect chassis stability.
A floating structure uses spring preload and controlled vertical travel to allow the drive wheels to move upward under the vehicle's weight. Once the system reaches static equilibrium, the drive wheels and auxiliary wheels can maintain contact with the floor, allowing the auxiliary wheels to carry part of the vehicle load.
However, maintaining contact between all wheels does not mean that every wheel carries the same load. Actual load distribution depends on the vehicle's center of gravity, spring stiffness, preload, wheel positions, and chassis design.
2. Improving Drive Wheel Adaptability to Floor Conditions
When an AGV passes over a depression or low section of the floor, a rigidly mounted drive wheel may lose contact because of changes in the relative position between the chassis and the ground. This can cause wheel spin or a reduction in vehicle traction.
A floating structure allows the spring to push the drive wheel downward within its available travel, helping it follow changes in floor height and maintain the required normal force and traction.
When the wheel encounters a raised section, the drive unit can move upward and compress the spring. This reduces the direct impact transmitted from the floor to the chassis and drive module.
The compensation capability of a floating structure is limited by its maximum compression and extension travel. If the floor irregularity exceeds the available movement range, the drive wheel may still lose contact with the ground.
3. Reducing Impact Loads on Drive Components
When an AGV operates on an uneven floor, impact loads can pass from the drive wheel through the mounting structure to the motor, gearbox, bearings, and chassis.
The spring in a floating suspension changes how these loads are transmitted through compression and rebound. This reduces the instantaneous impact that can occur with a rigid connection. Proper selection of spring stiffness and preload helps control drive unit movement and limit some of the impact loads.
If the assembly also includes a separate damper or materials with damping characteristics, continued oscillation after spring rebound can be further reduced. In contrast, a spring without sufficient damping may cause the drive unit to continue moving up and down after an impact.
Spring support and damping should therefore be matched to the AGV's travel speed, vehicle weight, floor conditions, and the movement characteristics of the floating mechanism.
3. Design Considerations for AGV Floating Suspension Structures
Although floating mechanisms have different movement patterns, their designs must account for drive wheel contact force, spring characteristics, and mechanical travel limits.
1. Spring Stiffness and Preload
Spring stiffness determines the force generated for a given amount of spring compression. If the spring is too stiff, the drive unit may not move sufficiently to accommodate floor irregularities, and more impact may be transmitted to the chassis. If the spring is too soft, it may not provide enough support force to maintain drive wheel contact.
Preload refers to the initial force applied to a spring in its installed condition. An appropriate preload helps maintain the required normal force on the drive wheel under different vehicle load conditions.
2. Floating Travel
Floating travel determines the range of floor height variation that the drive unit can accommodate. Both upward compression travel and downward extension travel must be considered.
If the compression travel is insufficient, the drive wheel may push the chassis upward when it encounters an obstacle. If the extension travel is insufficient, the drive wheel may be unable to follow the floor when passing over a depression.
3. Drive Wheel Contact Force
The normal load on the drive wheel directly affects the maximum traction force it can generate. Insufficient contact force can cause wheel slip, while excessive force increases the load on the tread, bearings, drive shaft, and mounting structure.
The suspension design must balance traction requirements, the load carried by the auxiliary wheels, and the allowable loads of individual components.
4. Alignment and Fit of Pivot and Guide Components
Pivot shafts, guide posts, bushings, and connecting brackets in the floating mechanism must have appropriate mounting positions and fits. Misalignment in the guide structure can generate additional lateral forces, causing moving components to bind or wear prematurely.
For four-bar and scissor-linkage mechanisms, the positions of the pivot joints, linkage movement paths, and structural deformation must also be checked to ensure smooth movement throughout the available floating range.
4. Custom Machining for AGV Floating Suspension Components
AGV floating suspension mechanisms contain various mechanical connecting and supporting components, including drive unit mounting bases, swing arms, pivot shafts, guide posts, guide bushings, bearing housings, connecting links, and support brackets. The dimensional accuracy, mounting positions, and mating fits of these parts affect the movement and load capacity of the suspension assembly.
For non-standard AGV chassis designs, these components often need to be manufactured according to the drive unit installation space, load requirements, and available floating travel. Hansheng Automation provides CNC precision machining of these metal structural components according to customer-supplied engineering drawings.
Our drawing-based machining services also cover precision components for other industries, including yacht structural parts, tobacco packaging machinery components, RC racing car metal parts, and filling equipment components. Manufacturing is arranged according to the dimensions and assembly requirements of each part.
