Procedure controlling the motor of a crane

The present invention relates to a procedure for selecting the mode of controlling the motor of a crane, or an equivalent lifting apparatus, when at least two alternative modes of controlling the motor are available, and at least one of the modes involves control by means of a switch having at least two positions connectable in a predetermined order, so as to produce corresponding control signals at a control input port. Each control mode uses at least one control signal common to all modes. According to the invention, the control signals applied to a control input port are monitored, the prevailing control situation is determined on the basis of the monitored signals and the mode of control is selected on the basis of which ones of the signals are active and the prevailing control situation.

FIELD OF THE INVENTION 
The present invention relates to a procedure for selecting the mode of 
control of the motor of a crane or an equivalent lifting apparatus. 
BACKGROUND TO THE INVENTION 
It is often necessary to be able to control the motor of a crane or an 
equivalent lifting apparatus from several locations In this case, care 
must be taken that only one control location is active at a time and that 
an operation once started can be completed without being influenced by 
another operator. 
The motor is generally controlled by means of push-button controllers which 
select the direction of motion, and the length of time during which the 
push-button switch is closed determines the speed reference for the motor 
control system. An alternative is the joystick controller, in which the 
joystick position determines both the direction and the speed reference 
value. Push-button controllers are typically used in hanging controllers, 
which are located near the load to be lifted, whereas joystick controllers 
are commonly used in the control cabin of a crane. 
The mode of operation (i.e. push-button or joystick) is typically selected 
by means of a separate selection switch, which can be placed, for example, 
in the control cabin In addition to the selection switch, the cabin must 
be provided with appropriate wiring for the selection signal, and the 
motor controller must be provided with an extra input for this purpose. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a system permitting the 
selection of the control mode without the use of a separate switch and 
associated wiring, and thus to produce a simpler and more reliable 
connection. 
According to the present invention, there is provided a procedure for 
selecting the mode of control of a crane motor when at least two 
alternative modes of controlling the motor are available, each of which 
control modes supplies a set of control input signals to respective 
control input ports of a motor controller, wherein each control mode 
involves at least one control signal common to all modes and the temporal 
order in which the various control signals are activated is characteristic 
of each respective control mode, said procedure comprising the steps of: 
monitoring the control signals being applied to the control input ports of 
the motor controller; determining the prevailing control situation on the 
basis of the monitored control signals; and selecting the mode of control 
on the basis of the monitored control signals and the prevailing control 
situation.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
As shown in FIG. 1, the motor 2 of a lifting apparatus 1 is controlled by 
means of a control unit 3 The control unit 3 is conventionally fed from 
the mains (not shown) and converts the mains voltage into a form (i.e. 
a.c./d.c. conversion) suited for the motor type, and controls the motor in 
accordance with input control commands The input control commands for the 
apparatus are provided by means of two controllers 4 and 5, each of which 
can normally be used to control the horizontal and vertical motions of the 
crane. The motions in each direction are controlled by separate joysticks, 
push-buttons or equivalents. 
A first controller 4 is implemented using potentiometer control (PO 
control), in which case the operator's control is a stepless movable 
control device or controller, such as a joystick. The control port of the 
control unit 3 typically has three inputs connected to the operator's 
control device These inputs are for the first and second direction signals 
(obtained when the control device is turned to the first and second 
directions respectively) and for an analog speed reference signal, which 
is proportional to the control device (i.e joystick) position The speed 
reference signal may vary between 0-10, for example, corresponding to a 
speed range of 0%-100% of the maximum motor speed. The analog reference 
may also contain a component determining the direction of motion, in which 
case its range of variation could be, for example, -10 to +10 V, 
corresponding to a speed range of -100% to +100%. 
A second controller 5 is implemented as a push-button controller based on 
so-called electronic potentiometer control (EP control) For each direction 
of the crane motion (i.e. up, down, forward, backward, right, left) the EP 
controller 5 has a separate push-button used to control the speed and 
duration of the motion in the direction concerned The push-buttons used in 
crane drive systems are generally of the two-position type, in which the 
first position determines the start of motion in a particular direction, 
and a so-called initial acceleration, as well as the maintenance of the 
velocity of the level attained. The second position of the push-button 
determines the time-derivative of the speed reference signal to produce a 
given rate of acceleration until the maximum speed is reached. Releasing 
the push-button completely causes the motor to decelerate in a controlled 
manner down to zero speed. 
In the control mode used by the PO controller 4, the speed reference signal 
input is always activated first and the controller position always 
corresponds to the value of the speed reference signal. In the control 
mode used by the EP controller 5, the signal determining the direction is 
always activated first and only then can the speed reference signal be 
activated. The control unit 3 is provided with a monitoring circuit which 
senses the temporal order in which the control unit inputs are activated, 
i.e. whether the speed reference signal input in the control port is 
active when one of the direction inputs is active. FIG. 2 shows a flow 
diagram illustrating the selection of control mode. 
If the motor speed is not equal to zero, operation of the controller 
continues in the control mode currently in use. If the speed is zero and 
the speed reference signal input is active but the direction signal inputs 
inactive, the control mode of the PO controller 4 is selected. Conversely, 
if a direction input signal is active and the speed reference signal 
inactive the control mode of the EP controller 5 is selected. In other 
cases, the current control mode is maintained. Thus, the control mode is 
selected according to the order in which the control signals obtained from 
the controllers are activated, without using a separate selection switch. 
The physical implementation of the monitoring and selecting circuitry can 
be accomplished using techniques belonging to the expertise of a person 
skilled in the art and therefore will not be described in detail herein 
FIG. 3 presents a timing diagram illustrating the selection of control mode 
when control commands are given in different ways. Curves a and b 
represent the changes of the control signals with respect to time while 
curves c and d represent the selection of the control mode on the basis of 
the control signals, in accordance with the selection logic described 
above. At Time T.sub.1, the speed reference signal 6 is on, while the 
direction signal 7 is off. Accordingly, the PO controller is selected, and 
subsequent changes in the direction signal 7 have no effect on the 
selected mode. At Time T.sub.2, the speed is zero, and the direction 
signal 8 is turned on while the speed reference signal (at least 
momentarily) remains off. Accordingly, the EP controller 5 is selected, 
and subsequent changes in the speed reference signal 9 have no effect on 
the selected mode. 
In this procedure, it is naturally necessary to take care that all the 
controllers and controller positions in each control device are included 
in the selection process. This prevents simultaneous use of the controller 
at one control point for a lifting movement and another controller for a 
traversing motion, for example. 
In the foregoing, the invention has been described by referring to some of 
its embodiments. However, this presentation should not be regarded as 
restricting the invention, but the scope of the patent may vary within the 
limits defined in the following claims.