Control system for positioning implements

A control system for positioning an implement using a power steering unit. Instead of connecting a rotary spool of the power steering unit with a steering wheel, the rotary spool is connected with a DC motor through reduction gears. An angular displacement of a control lever is detected by an angular position detector and an angular displacement of an implement is detected by another angular position detector. Signals from both detectors are fed into a comparator which is connected with an amplifier for rotating the DC motor in either direction in response to signals therefrom.

BACKGROUND OF THE INVENTION 
This invention relates to a control system for positioning implements of 
construction vehicles and implements such as manipulators etc. 
In the conventional electric-hydraulic servo systems serving as a 
positioning device of the kind specified, electric-hydraulic servo valves 
are generally employed for conducting electric-hydraulic conversion. The 
electric-hydraulic servo valves are however expensive in cost and are 
liable to cause troubles when dust etc. enters them and when they undergo 
vibration, and therefore their applications are restricted. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a control 
system for positioning an implement which is simple in construction and 
inexpensive to manufacture. 
Another object of the present invention is to provide a control system for 
positioning an implement which is reliable in operation and can be used in 
various environmental conditions. 
In accordance with an aspect of the present invention, there is provided a 
control system for positioning an implement, comprising: a source of 
pressurized fluid; a power steering unit including a rotary valve having a 
sleeve and a rotary spool rotatably received in the sleeve and metering 
means operatively associated with the rotary valve for metering 
pressurized fluid from said source in response to an annular displacement 
of the rotary spool relative to the sleeve; an implement pivotally mounted 
on a body; cylinder means connected with said power steering unit for 
angularly displacing said implement; first angular position detector means 
for detecting an angular displacement of said implement relative to said 
body; an operating lever means pivotally mounted on said body for 
operating said implement; second angular position detector means for 
detecting an angular displacement of said operating lever means relative 
to said body; comparator means connected with said first and second 
angular position detector means for comparing signals therefrom and 
generating an output signal; amplifier means for receiving the output 
signal from said comparator means and generating an output signal 
therefrom; and DC motor means connected with said amplifier means and said 
rotary spool of said rotary valve for rotating said rotary spool in 
response to the output signal from said amplifier means. 
The above and other objects, features and advantages of the present 
invention will be readily apparent from the following description taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will now be described by way of example only with 
reference to the accompanying drawings. 
In FIG. 1, reference numeral 1 denotes a power steering unit which is used 
in the steering system of vehicles having large-sized wheels and which is 
an application of servo machanism wherein a mechanical displacement 
obtained by the manipulation of steering wheel is converted in a 
displacement by fluid pressure exerted through a hydraulic cylinder. 
Steering units of this type require limited number of component parts and 
are low in manufacturing cost with a high reliability. Further, they are 
characterized in that rotary valves thereof can be turned continuously 
without limitation in angle of rotation at a low input torque. 
The power steering unit 1 comprises a power system portion 2, a direct 
mechanical link 3, and a metering means 27 having a gerotor. 
The construction of the steering unit 1 is shown in FIG. 2, in which 
reference numeral 20 denotes a unit marketed as an element of steering 
system for wheeled vehicles. 
The operating principle of the steering unit 1 will now be described below. 
A spool 21 which is an input shaft of the steering unit 1 (and is usually 
coupled with a steering wheel) and a sleeve 22 form a rotary valve 23. The 
arrangement is made such that the spool 21 is turned to cause an angular 
displacement between the spool 21 and the sleeve 22 to thereby conduct 
change-over of oil passages. 
Further, when no external force is applied to the spool 21, the rotary 
valve 23 is held at its neutral position by the action of a centering 
spring 24 inserted between the spool 21 and the sleeve 22. (Refer to FIG. 
3). The fluid pressure delivered by a hydraulic pump is supplied from an 
inlet port P and through the rotary valve 23 and thence into a front 
chamber P.sub.1 or P.sub.2 of a metering device 27 comprising a gerotor 
ring 25 and a gerotor star 26. (Refer to FIG. 5). The metering device 27 
is a kind of inscribed gears employing, for example, as shown in FIG. 5, 
trochoid curves for their teeth shapes and which is constituted by the 
gerotor ring 25 (stator) having seven gear teeth and the gerotor star 26 
(rotor) having six gear teeth and has a metering function to discharge 
fluid under pressure in volume in proportion to the displacement of the 
spool 21 of the rotary valve. 
Further, the gerotor star 26 is mechanically connected through a drive 
shaft 28 to the sleeve 22 to provide a feed back effect (Refer to FIG. 4). 
This drive shaft 28 corresponds to the mechanical link 3 in FIG. 1. An 
output shaft of a motor 6 (DC motor) is connected to the spool 21 of the 
rotary valve 23. The rotary valve 23 has ports 23a and 23b and which ports 
are connected through conduits 8 and 9, respectively, to an operating 
cylinder 11 of an implement 10. An angular position detector 12 is located 
at the fulcrum of the implement 10. 
In FIG. 1, reference numeral 13 denotes an operating lever which has an 
angular position detector 14 fitted at its fulcrum of turning. The output 
sides of these angular position detectors 12 and 14 are both connected to 
the input side of a comparator 15, the output side of which is connected 
to the input side of a servo amplifier 16, the output side of which is 
connected to the input side of the motor 6, thus forming a closed loop 
control system. 
The operation of the control system according to the present invention will 
now be described below. 
If and when the control lever 13 is moved to a certain position in a 
direction for raising the implement, the angular position detector 14 will 
detect the movement and generate a command signal corresponding to the 
position of the lever 13 which is sent into the servo amplifier 16 to 
thereby drive the motor 6 in a predetermined direction. As a result, the 
rotary valve 23 of the power steering unit 1 will be driven so as to allow 
the fluid under pressure from the power system 2 to be supplied into the 
hydraulic cylinder 11 thereby raising the implement 10. When the implement 
10 has reached a target position, the deviation in signal between the 
angular position detector 12 of the implement 10 and the angular position 
detector 14 of the control lever 13 becomes zero so that the rotation of 
the motor 6 is stopped, the steering unit 1 is moved to its neutral 
position and the implement 10 is held at the target position. The same 
operating principle is applicable to the case of lowering the implement 
10. The power steering unit is constructionally disadvantageous in that 
the actuator connected thereto tends to cause the neutral position to get 
out of place unless it can supply equal amount of fluid under pressure to 
either of leftward or rightward movement like, for example, hydraulic 
motors and double-rod hydraulic cylinders. However, in the system shown in 
FIG. 1, there is provided a feed back circuit which detects the position 
of the actuator, for example, the operating cylinder itself, there is no 
risk of the neutral position getting out of place even if a single-rod 
hydraulic cylinder is employed. In this case, however, the moving speeds 
of the implement when it is raised and lowered differ from each other. 
If a signal from a microcomputer, a function generator or any other 
controller is sent to the servo amplifier 16 instead of the signal from 
the angular position detector 14 of the control lever 13, it is possible 
to move the implement as desired. Therefore, the present invention is 
applicable to automatically actuated machines such as industrial robots 
etc. 
It is to be understood that the foregoing description is merely 
illustrative of a preferred embodiment of the present invention, and that 
the present invention is not to be limited thereto, but is to be 
determined by the scope of the appended claims.