Coordinated joint motion control system with position error correction

Abstract

Disclosed are an articulated hydraulic machine supporting, control system and control method for same. The articulated hydraulic machine has an end effector for performing useful work. The control system is capable of controlling the end effector for automated movement along a preselected trajectory. The control system has a position error correction system to correct discrepancies between an actual end effector trajectory and a desired end effector trajectory. The correction system can employ one or more absolute position signals provided by one or more acceleration sensors supported by one or more movable machine elements. Good trajectory positioning and repeatability can be obtained. A two joystick controller system is enabled, which can in some cases facilitate the operator's task and enhance their work quality and productivity.

1 . An articulated hydraulic machine supporting an end effector for performing useful work, the articulated hydraulic machine comprising a control system capable of controlling the end effector for automated movement along a preselected trajectory wherein the control system comprises the generation of reference positions for each of multiple controlled movable machine elements according to a software-defined differential kinematics configuration, and applies a position error correction system to correct discrepancies between the actual and the desired machine element trajectories and wherein the error correction module:
 a) compares the actual end effector position at a given point in time with a reference position appropriate for the desired end effector trajectory;   b) generates a difference between the actual end effector position and the reference position; and   c) applies a correction signal to the machine to reduce the difference.   
     
     
         2 . A machine according to  claim 1  wherein the reference position is modeled for a hypothetical model machine, using a software-defined differential kinematics configuration, under identical control command to that of the real machine, save for the corrections 
     
     
         3 . A machine according to  claim 1  wherein the control system comprises two operational parts respectively capable of separately processing a reference position vector according to a software-defined differential kinematics and an actual position vector. 
     
     
         4 . A machine according to  claim 3  wherein the reference position vector and the actual position vector are actively connected using a closing control loop which compares the actual position vector with the reference position vector and generates the correction signal. 
     
     
         5 . A machine according to  claim 1  wherein the machine provides to the control system absolute position information regarding at least one movable machine element to facilitate determination of the end effector position. 
     
     
         6 . A machine according to  claim 1  wherein the machine has multiple movable machine components contributing to movement of the end effector and the absolute position information comprises absolute position information regarding each movable machine element. 
     
     
         7 . A machine according to  claim 1  wherein the position error correction system comprises at least one of a joint control model, a machine actuators model and a dynamic machine model. 
     
     
         8 . A machine according to  claim 1  wherein the position error correction system comprises a joint control model, a machine actuators model and a dynamic machine model. 
     
     
         9 . A machine according to  claim 1  wherein the position error correction system can operate to correct velocity error. 
     
     
         10 . A machine according to  claim 1  comprising at least one acceleration sensor, the or each acceleration sensor being supported by a machine element, to provide absolute position signals regarding the respective machine element. 
     
     
         11 . A machine according to  claim 6  wherein an accelerometer is provided at or on each movable machine element. 
     
     
         12 . A machine according to  claim 1  wherein the control system employs model-based forward prediction to predict a next movement of a machine element and scale the predicted movement to provide desired movement. 
     
     
         13 . A machine according to  claim 1  wherein the control system applies the correction signal kinematically, providing continual incremental adjustments while the machine is moving to execute a specified end effector trajectory. 
     
     
         14 . A machine according to  claim 1  comprising a coordinated joint motion system including:
 a) support; 
 b) multiple links; 
 c) multiple joints, optionally revolute or prismatic joints, connecting the links one to another and to a support, each joint permitting relative movement between the connected members; 
 d) multiple actuators to effect said relative movement between the connected members, the multiple actuators being controlled by the coordinate joint control system; and 
 e) an end effector supported by the jointed links for movement relative to the support; 
 
       wherein the coordinated joint motion system is capable of execution of an automated end effector trajectory without human intervention wherein the coordinated joint control system comprises an operator interface enabling a human supervisor to change the end effector motion or position during execution of the automated trajectory. 
     
     
         15 . A machine according to  claim 14  comprising an internal feedback loop to determine a mathematical model of the coordinated joint motion system and provide a model-based forward predictor for directly controlling the joint actuators, optionally by employing a differential control architecture. 
     
     
         16 . A machine according to  claim 15  comprising a mining machine, a construction machine, an excavator, a front loader or a mechanical shovel. 
     
     
         17 . A machine according to  claim 16  wherein the multiple links comprise a boom revolutely connected to the machine, an arm revolutely connected to the boom and a tool, optionally a bucket, revolutely connected to the arm. 
     
     
         18 . A control system for a machine according to  claim 1 , the control system comprising a position error correction module to correct discrepancies between the actual end effector trajectory and the desired end effector trajectory, wherein the error correction module:
 a) compares the actual end effector position at a given point in time with a reference position appropriate for the desired end effector trajectory;   b) generates a difference between the actual end effector position and the reference position; and   c) applies a correction signal to the machine to reduce the difference.   
     
     
         19 . A method of controlling a machine according to  claim 1 , the method comprising prescribing a desired tool or end effector position to the controlled machine, comparing one or more reference positions appropriate for achieving the desired tool position with one or more actual machine element positions determined from an absolute sensor signal, generating a correction and applying the correction to improve the actual position.