GB2290149A

GB2290149A - System for ensuring the stability and safe operation of lift trucks

Info

Publication number: GB2290149A
Application number: GB9411623A
Authority: GB
Inventors: Colin Stanley Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-06-10
Filing date: 1994-06-10
Publication date: 1995-12-13
Also published as: GB9411623D0

Abstract

A method of ensuring the stability and safe operation of appliances for lifting or carrying, such as lift trucks, uses sensors which monitor the loading at each wheel to detect potential overturning of the vehicle. These sensors can interact with other sensors which detect one or more other parameters of the vehicle such as the steering position or the speed. Visual or audible warnings may be given or manual control of the vehicle may be limited, eg to restrict the speed in accordance with the weight of the load.

Description

SYSTEM FOR ENSURING THE STABILITY AND SAFE OPERATION OF LIFT TRUCKS A method of detecting overloading or excessive moment on an appliance for lifting or carrying comprises sensors to detect the loading at each wheel interacting with sensors to detect one or more other functions of vehicle configuration including, for example, velocity, level, load position, and steering position.

This type of system relates particularly, but not exclusively, to counterbalanced lift trucks, stacking lift trucks, pallet stackers, platform high-lift trucks, stacking lift trucks with elevated operator, side-loading trucks, rough terrain fork trucks, lateral stacking trucks, lateral and front stacking trucks, order picking trucks, and straddle carriers.

Lift trucks present a serious safety hazard. The primary danger presented by such appliances is the possibility of overturning. Overturning may be caused by a combination of a number of factors including; 1. Maximum load exceeded 2. Maximum moment exceeded 3. Dynamic forces move centre of gravity beyond area of stability due to severe braking, load positioned too high, terrain too rough, turning speed too high, or ground/floor not level.

4. Load centre is sideways-biased.

These effects may be further compounded by the angle of the mast where a tiltable mast is fitted. As a load is raised on a machine with a mast not at vertical, the mass of the load may cause the the overall centre of gravity to move beyond the area of stability.

Existing methods of preventing overturning utilise systems for sensing the load being carried directly by the forks, etc, typically by load cells or hydraulic pressure transducers.

The system is sometimes improved by interlinking a device to ascertain the relative angular position of the mast, giving reduced maximum load for forward mast positions. This system is only capable of detecting maximum overload. This restriction still leaves the truck unprotected from several of the potential cause of overturning. The standard method of protection from these additional hazards is driver training.

The majority of trucks have no warning systems.

This invented system for ensuring stability uses sensors to detect the loading at the wheels, suspension or other point representing a relative value of wheel loading. The basis for detecting overturning and/or overloading is that either a maximum or minimum load value will represent these conditions.

If overturning is about to occur, the load on one or more wheels will reduce until that wheel is at the point of lifting when a minimum wheel loading value will occur. This effect occurs irrespective of the direction of overturning, so that sideways-overloading is equally detected. If overloading occurs, one or more wheel(s) will receive a maximum load value. The output from the sensors can be used for visual or audible warning to the operator, including graduated levels of warning or, alternatively, to reduce the level of danger by automated control, or limitation of manual control. All monitoring inputs and outputs are integrated through a control system which may be a PLC (programmable logic controller) or electronic circuitry for the purpose.A variety of methods are available for sensing the wheel loading including load cells, hydraulic pressure systems, and component deflection methods.

The values of maximum and minimum wheel loading to give warning output are initially set to suit the configuration of the vehicle. These initial settings may include a bias, for example, between front and rear wheels and, on sideloaders, a bias between sides. The values may be also set to accommodate wheel configurations where other than four wheels are used.

On some wheel configurations, it may not be necessary to monitor all wheel loadings.

In operation, initial settings may be adjusted in value with input from other vehicular functions. These functions may include vehicle speed (or any other such equivalent), level of vehicle, load position, and steering position. The requirement is to reduce the maximum load and/or moment to a safe level when other criteria would make the normal capacity otherwise dangerous, or alternatively, to restrict functions to values determined by the sensor output values.

An example of the above mentioned process is in relation to vehicle speed. A maximum load or moment is set and safe for static operation. As the vehicle gains speed, the potential to overturn the truck by the dynamic effects of braking or manoeuvring increases. A sensor detects the speed of the vehicle and continually adjusts the maximum load or overturning condition to suit. If the vehicle loading achieves or exceeds this reduced setting, a warning is given and the operator can reduce speed accordingly. Alternatively, as the reduced maximum load condition is achieved, the vehicle is automatically prevented from gaining increase in speed.

Another example is in relation to level of vehicle. A vehicle operating on a sloping area has a much increased chance of overturning. Overturning of the vehicle is automatically sensed by minimum wheel loading condition. It may be desirous, however, to decrease the maximum load under such conditions. Sensors are fitted to the vehicle to detect the divergence from true level. A number of sensing means are available for this purpose. The system may detect front-rear divergence, side-side divergence or divergence in other planes. As the divergence increases, so the maximum allowable load decreases. If this reduced maximum is achieved or exceeded, a warning will be given, and the operator can take appropriate action to remove the danger. This system will include allowance for differences created by vehicle layout.

For example, a fork lift truck can have greater capacity moving uphill with forks first, than with forks to the rear.

A further example of the system would be in relation to load position. The dynamic effects on a load in respect of overturning are increased as the load is raised. Sensors are fitted to the machine to monitor the height to which the load is raised. The output from the sensors is used to reduce the allowable capacity in a similar manner to the aforementioned examples. As the reduced capacity is achieved or exceeded, an alarm is given to enable the operator to work within safe parameters. A further option is automatic lowering of the load to a safe level. This latter option is only acceptable if suitable safeguards are made to ensure that the load and/or vehicle carrying structure would not cause a separate hazard in the lowered position.

A further example is in relation to steering position. As the steering is turned, centrifugal force acts upon the load and vehicle. The force generated is a resultant of steering position, and vehicle speed. A sensor (systems are readily available) detects the degree to which the steering is divergent from straight ahead. As this divergence increases, so the capacity of the machine should decrease. This function is usually integrated with vehicle speed. The resultant decrease in capacity sounds the alarm or, alternatively, reduces vehicle speed if the reduced capacity is achieved or exceeded.

Outputs from the separate monitoring sensors may be integrated to produce a combination reduction in capacity. One example of this system uses the individual sensor outputs to determine a multiplier factor. Each multiplier is then applied to the static capacity, resulting in a combined, reduced capacity.

Claims

This invention claims; A) A system for ensuring the stability and/or safe loading of appliances such as fork lift trucks by means of detection of the loading at the wheels.

B) A system as described in paragraph A in which the loading at the wheels is detected by means of load cells, hydraulic or other devices attached to the axles or suspension which monitor pressure, or devices attached to the axles or suspension to monitor deflection due to changes in loading.

C) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of stability.

D) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of overload.

E) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of excessive moment.

F) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of stability due to excessive sideloading.

G) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of overload due to the load being offset.

H) A system as described in paragraphs A or B in which a minimum or maximum sensor value or combination of values is used to detect a condition of excessive moment due to an offset load.

I) A system as described in paragraphs A, B, C, D, E, F, G, or H in which the output from the sensors is used to give a visual or audible warning of the condition.

J) A system as described in paragraphs A, B, C, D, E, F, G, or H in which the output from the sensors is used to give a visual or audible warning of graduations of the condition.

K) A system as described in paragraphs A, B, C, D, E, F, G, or H in which the output from the sensors is used to give reduced level of danger by limitation of manual control.

L) A system as described in paragraph R in which the limitation of manual control prevents the operator from exceeding a preset, or determined vehicular speed.

M) A system as described in paragraph K in which the limitation of manual control prevents the operator from exceeding a preset, or determined maximum height of load.

N) A system as described in paragraphs A, B, C, D, E, F, G, or H in which the output from the sensors is used to give reduced level of danger by automated control of the vehicular functions.

O) A system as described in paragraph N in which vehicle speed is automatically reduced.

P) A system as described in paragraph N in which load height is automatically reduced.

Q) A system as described in paragraphs A, B, C, D, E, F ,G or H in which the minimum, maximum, or interim sensor output values are set to accommodate the configuration of the vehicle.

R) A system as described in paragraph Q in which the minimum, maximum, or interim sensor output values are set with front/rear or side/side bias to accommodate the configuration of the vehicle.

S) A system as described in paragraphs A to R inclusive in which the settings of minimum, maximum or interim loadings are adjusted in value as a response to data from other sensors on the vehicle.

T) A system as described in paragraph S in which vehicle speed (or equivalent) is used for input data.

U) A system as described in paragraph S in which the level of the vehicle (in one or more planes) is used for input data.

V) A system as described in paragraph S in which the position of the load is used for input data.

W) A system as described in paragraph S in which the position of the steering mechanism is used for input data.

X) A system as described in paragraphs S, T, U, V, and W in which the outputs from more than one sensing function are integrated to determine a modified machine capacity.

Y) A system as described in paragraphs A to X inclusive in which not all the wheels are used for determining overturning and capacity characteristics.

Z) A system as described in paragraphs A to Y in which the sensing data is processed in either a PLC (programmable logic controller) or a purposely designed electronic system.