The invention generally relates to robotic and other sortation systems and relates in particular to programmable motion systems having an articulated arm with an end effector that employs vacuum pressure to engage objects in the environment.
Most vacuum grippers employ vacuum pressures well below 50% of atmospheric pressure, and are referred to herein as high vacuum. A typical source for a high vacuum gripper is a Venturi ejector, which produces high vacuum but low maximum air flow. Because of the low flow, it is essential to get a good seal between a vacuum gripper and an object, and it is also important to minimize the volume to be evacuated.
The principle of the Venturi pump for generating vacuum is that compressed air blown over an aperture generates negative differential pressure at the aperture. The compressed air is typically generated by a large compressor that will feed multiple pneumatic systems. Switching of the vacuum is thus performed through a valve which switches on or off the supply of compressed air to the Venturi pump. Thus, Venturi-based systems for vacuum gripping have two states: on or off.
Suppliers of ejectors and related system components include Vaccon Company, Inc. of Medway, MA, Festo US Corporation of Hauppauge, NY, Schmalz, Inc. of Raleigh, NC and others. In some instances where a good seal is not possible, some systems use high flow devices. Typical high flow devices are air amplifiers and blowers, which produce the desired flows, but cannot produce the high vacuum of a high vacuum source. High flow sources include the side-channel blowers supplied by Elmo Rietschle of Gardner, Denver, Inc. of Quincy, IL, Fuji Electric Corporation of America of Edison, NJ, and Schmalz, Inc. of Raleigh, NC. It is also possible to use air amplifiers as supplied by EDCO USA of Fenton, MO and EXAIR Corporation of Cincinnati, OH. Multistage ejectors are also known to be used to evacuate a large volume more quickly, wherein each stage provides higher levels of flow but lower levels of vacuum.
Despite the variety of vacuum systems, however, there remains a need for an end effector in a robotic or other sortation system that is able to accommodate a wide variety of applications, involving engaging a variety of types of items. There is further a need for an end effector that is able to provide high flow and that is able to handle a wide variety of objects weights.
In accordance with an aspect, the invention provides a system for providing high flow vacuum control to an end-effector of a programmable motion device. The system includes a vacuum source for providing a high flow vacuum, a conduit path leading from the end-effector to the high flow vacuum source, a sensor system for sensing any of a pressure or a flow at any of the end-effector, the conduit path, and the vacuum source, and providing sensor information, and a pneumatic control module including a vacuum pressure adjustment system for adjusting the high flow vacuum within the conduit path responsive to the sensor information.
In accordance with another aspect, the invention provides a system for providing high flow vacuum control to an end-effector of a programmable motion device. The system includes a high flow vacuum source including a rotating element that provides a high flow vacuum at the end-effector when the rotating element is rotating at a first rotational speed, and a pneumatic control system for a first period of time between discharge of a first object being grasped and an initial grasp of a second object to be grasped subsequent to the first object, and a second period of time that is less than the first period of time during which power to the rotating element is decreased and subsequently increased such that the rotating element returns to the first rotational speed prior to grasping the second object.
In accordance with a further aspect, the invention provides a method of providing high flow vacuum control to an end-effector of a programmable motion device. The method includes providing, using at least in part a rotating element, a high flow vacuum at the end-effector when the rotating element is rotating at a first rotational speed, identifying a first period of time between discharge of a first object being grasped and an initial grasp of a second object to be grasped subsequent to the first object, decreasing power to the rotating element for a second period of time that is less than the first period of time, and increasing rotational speed of the rotating element prior to grasping the second object.
The following description may be further understood with reference the accompanying drawings in which:
The drawings are shown for illustrative purposes only.
In accordance with an aspect, the invention provides an electromechanical and pneumatic system for performing unit handling tasks for a wide variety of items. In accordance with various aspects, the invention provides an end-effector system for programmable motion devices (e.g., robotic systems) that provides high flow vacuum to grasp objects. The high flow vacuum is provided at a vacuum cup as the end-effector of the end-effector system that is coupled to a high flow vacuum system. The vacuum cup is attached to a cup attachment portion, which is in turn attached to an arm attachment portion that is attached to an articulated arm of the robotic system.
With reference to
In accordance with various aspects, the invention provides the design of an electromechanical and pneumatic system for performing unit handling tasks with a wide variety of items, as well as the behaviors enabled by such a design. An illustrative diagrammatic schematic view of the hardware system is shown in
The pneumatic control module 40 includes a pressure and flow meter 42 coupled to the vacuum hose 12, which is coupled to a tee-fitting 44. The output of the tee-fitting 44 is passed through a filter 46, then through a blower 48 leading to an exhaust muffler 50. A source of fresh air bypass 52 is provided via an air valve 54 to the tee-fitting 44, and the blower 48 is controlled by a variable frequency drive 56 coupled to a 1-phase/2-phase/3-phase power source 58.
As shown in
The vacuum hose 22 is a flexible conduit for coupling to the vacuum source that allows the robotic articulated arm 12 to move in the workspace. The hose length and diameter are chosen to minimize pressure loss. The hose length is no longer than required to allow the robot to move freely in the required workspace, e.g., about 10 to 20 feet. The hose diameter balances the time required to evacuate the air in the hose and the pressure losses from choosing a narrower hose, e.g., about 2 inches.
The tee-fitting provides an air manifold for three connections: the pipe going to the gripper; the pipe going to the blower; and the valve. The straightaway section of the tee-fitting 44 connects the gripper and blower pipes, which minimizes the total pressure drop at the gripper at high flow rates. The base of the tee-fitting 44 connects to the valve 54. In this system design, the valve 54 is not in the flow path from the gripper 30 to the blower 48. The valve 54 opens to allow fresh air (via bypass 52) to flow with a minimum impedance to the blower 48.
The valve 54 may be a butterfly valve that when open allows ambient air to enter the tee-fitting 44. When the valve is open, because of the resistance or pressure drop of the hose 22, air will flow through the valve 54 and tee-fitting 44 to the blower 48, and there will be minimal negative pressure at the suction cup. When the valve 54 is closed, the conduit is a closed system from the blower 48 to the suction cup 34 opening and the blower 48 pulls air from the suction cup 34. In addition to butterfly valves, other types of valves may be effective, such as a poppet valve, a ball valve, a gate valve, etc. A butterfly valve is balanced and requires minimal torque to actuate, though care should be taken to ensure that the butterfly plate (or disc) does not deform under the vacuum pressure.
The filter 46 prevents debris or detritus from entering the blower 48. The filter 46 may be a cylindrical axial filter with an inlet and an opposing outlet that is otherwise sealed. Air passing from inlet and outlet goes through a removable air filter. The blower 48 is the high flow vacuum source and may be a regenerative blower, centrifugal blower, or positive displacement blower such as a rotary vane, or claw vacuum pump, or may be some other vacuum source that produces a high flow vacuum. The blower may include a pressure and/or flow sensor 49 that provides sensor output information for the processing system(s). Providing the sensor information from a sensor 49 at the blower provides improved sensor data acquisition speed regarding grasp attempts at the end-effector in certain applications. The blower may be driven by an AC motor, and the AC motor may be controlled by the variable frequency drive (VFD) 56 which serves as the motor controller for the blower's motor using the 1-phase/2-phase/3-phase power source 58. The variable frequency drive 56 varies the frequency going to the motor for the blower 48, allowing the variable frequency drive 56 to set the speed and direction of the blower motor. The VFD 56 has the capacity to control ramp-up and ramp-down of the blower motor during start or stop, respectively. Control of motor speed allows control of the blower's maximum pressure and flow. With some blower technologies, such as a regenerative blower, directional control of the motor allows the air to reverse direction. The exhaust muffler 50 minimizes noise produced by outgoing air from the blower.
As also shown in
In accordance with various aspects therefore, the pneumatic control module may adjust either or both of the analog adjustable valve and/or the power to the blower (e.g., via frequency control) responsive to the sensor output information from the one or more sensors (e.g., 35, 42, 49). In accordance with further aspects, the system may identify an object being grasped (either prior to or during grasping) and the system may obtain object specific grasping information. The system may then adjust either or both of the analog adjustable valve and/or the power to the blower (e.g., via frequency control) responsive to the object specific grasping information. In accordance with further aspects, the system may adjust the valve 54 and/or power to the blower 48 responsive to either or both the sensor information and/or the object specific information and may further coordinate with the cup changing module 106 to provide an optimal choice of vacuum cup for a next object to be grasped. The system may, for example, determine that a different size vacuum cup should be used, instructing the programmable motion device to exchange cups as disclosed for example, in U.S. Patent Application Publication No. 2019/0217471, the disclosure of which is hereby incorporated by reference in its entirety. The system may determine this based on any of sensor data and object specific data, and may combine the cup change with adjusting either or both the valve 54 and/or power to the blower as discussed above. The system therefore provides finely adjustable high flow vacuum for a wide variety of objects including object packaging.
With reference to
When a porous object is being gripped, or an irregularly shaped object that resists sealing is being gripped, air will flow through or around the object.
With reference to
With reference to
With reference to
With reference to
The arrangements shown in
In accordance with further aspects, pneumatic control systems may employ more than one valve for increased pressure control. If a first valve has only two states, open and closed, then a second valve could be used to vent the system. This would not have the same high flow requirements, but might be a low cost solenoid valve to give an additional state of reduced pressure, or a servo valve that would be continuously variable. Another option is to employ a greater number of small flow valves that allow ambient air to enter, and then vary the number of valves that are opened in order to control maximum pressure.
The combined tee and valve design provides two key benefits. First, it allows for an unimpeded path from the blower to the suction cup, which as discussed above can facilitate gripping porous items. The maximum air flow at the suction cup is close to the maximum air flow of the blower. Second, the blower is generally always generating vacuum (exceptions are discussed below), so it prevents the blower from being deadheaded when the vacuum is not in use for gripping. The condition of deadheaded means the conduit to the blower inlet is sealed. Consider the alternative, where there was no tee but instead an in-line valve that was closed, then the space from the closed valve to the blower would be at maximum vacuum and have no flow. Air is therefore needed to pass through the blower to keep it from overheating, and so whether objects were being gripped or not, the blower would be deadheaded nearly 100% of the time. So instead, the open valve lets in ambient air, which cools the blower and prevents it from overheating. Furthermore, a regenerative blower, for instance, may exhibit significantly higher current draw (˜25%) when deadheaded.
Two important design variables are the diameter of the inlet to the valve, as well as the actuation time. The diameter of the valve needs to be large enough to have significantly lower pressure drop than the hose, so that when open, air takes the route through the valve and not the hose. In regards to actuation time, it is desired to be as low as possible, and so the mass of the disc is as low as can be while maintaining strength so as to minimize the torque required to actuate it. Other valve choices are possible, but a butterfly valve typically has low pressure drop and high speed actuation. A butterfly valve design supports valve actuation from on to off and off to on in the order of 100 milliseconds. The system application needs to wait at least this amount of time to detect whether a pick is successful based on this timing. There is a direct connection therefore to system throughput.
Another variable in the design is whether to include an additional relief valve. An additional valve may be used to reduce the possibility of deadheading the vacuum generator. Alternatively, the valve may be controlled to be partially open instead of closing fully. Another design might put the valve in-line, or in the path of air from suction cup to blower, i.e., not use a tee. In such cases it might be that the blower can tolerate deadheading, and that the pressure drop due to the valve is acceptable.
In the operating mode shown in
The second example is picking. During a picking trajectory the system can preemptively close the valve by, for example, 60% during robot arm motion so that when the robot arrives at the picking location, it can more quickly close all the way, with the effect of reducing latency waiting for the valve to close, and increasing system throughput. In general the trajectory control of the valve position can be coupled to or synchronized with trajectory control of the robot, so as to control timing of each to implement various behaviors, with the aim of increasing throughput or controlling the effects of the pneumatic system.
Pressure and flow sensors can be used to detect a variety of states. The pressure-flow illustrates that pressure and flow are subject to a constrained relationship; pressure provides information about flow and vice versa. Nevertheless, both sensing modalities can be used for redundancy, and to exploit advantages of each. Generally flow data will be noisier than pressure data, but pressure data will be slower to react to events.
Drop detection may be achieved by applying a threshold the pressure/flow data. This may also be done by monitoring for a drop in negative pressure or an increase in flow versus the initial value measured at the time the seal was determined to be a valid grasp. Signal processing and machine learning techniques may also be used to classify the pressure/flow signal as an imminent drop situation.
Successful pick detection may be determined by monitoring the pressure sensor's signal and detecting that some minimum negative pressure value is present. Depending on the cost of a drop of a poorly gripped object—one might want to monitor the grip-quality signal for some period of time before beginning to move the item. If maximizing throughput, then one might opt to start transferring the item once it is observed that a good grasp is imminent by monitoring the slope of the negative pressure instead of waiting for a specific threshold to be hit. This might lead to more early drops but would save time when detecting grips and early drops might result in the object returning to where it was picked from in the first place.
If item attributes are known, then a partial seal may be detected when maximum negative pressure is not achieved on a non-porous item and the system can decide whether to regrasp it or transfer it slowly. The system may therefore choose use of pressure or flow depending on the SKU's pick surface's attributes. For example, for a porous object, the system may use flow data instead of pressure for a clearer signal. For a porous object that is also small, where a small cup is used, the system may need to use flow data instead of pressure because the small cup will not provide a consistent minimum negative pressure to threshold on given the flow-pressure curve. For a porous object that is large, where a large cup is used, the system may also use flow data instead of pressure to detect successful grip. If the large cup allows for enough flow however, then the negative pressure will be higher up on the flow-pressure curve, so the system might be able to achieve a consistent detectable value.
When the robot is controlled by a real-time stream of high frequency waypoints from the high level software, its travel speed with the object in tow can be modulated by the grip quality to reduce drops. The system may choose to either (1) use a smaller cup with a high pressure seal or (2) use larger cup with a partial seal (relying on the high flow)—to achieve adequate grip-force to transfer an item. In accordance with further aspects, the system may detect a contour of the pick surface beneath the grasp location, and use this information to inform the quality of seal to be expected at the grip, which can inform the robot to switch to a larger cup before attempting the pick. In particular, the system may inform cup selection based on contours of the segment item's pick surface. Knowing this, the system may elect to execute a high flow pick or a high pressure pick depending on how the item is presenting in the tote. The system may also learn whether a partial seal is more likely on a given SKU using historical data and then opt for a larger cup despite the fact that the item is very light or smaller.
The system is able to check if an unexpected obstruction, such as trash, exists in any part of the pneumatic path (e.g. gripper, hose) between picking operations. This is done by closing the valve to enable suction, when the suction cup should be at a point in space in which no contact with a blocking surface is expected, such as mid-air in an open part of the workspace. The system may then check if negative pressure exists similarly to how the grip quality on an item is measured. If the conduit were unblocked, the pressure sensor should report atmospheric pressure. The same operation can be done using the flow sensor as well (e.g., trash in the hose is likely if the flow measurement is below some nominal flow value). To check for trash with a minimal throughput hit, the system may perform the check during the initial segment of a pick trajectory and interrupt it if an item is present. This requires knowing that the check will be performed while the gripper is far enough away from the object that is targeted to be grasped.
The system may also monitor residual flow when not picking to compare blower performance to historic performance, or to detect blockage, or other issues in the pneumatic system. In accordance with further aspects, the placement of flow and pressure sensors may affect timing. Sensors may be placed to minimize latency of detecting various kinds of events.
Pressure and flow sensors nearer the gripper for example, may provide an earlier indicator of the onset of a loss of seal compared with sensors near the valve. Additionally, pressure and flow sensors nearer the valve provide an earlier indicator of the onset of a seal compared with gripper-mounted sensors.
For the purposes of diagnosing or inferring the location of problems, two pressure/flow sensors may help resolve issues at different segments of the conduit (e.g., to determine whether the hose is more probably a problem or whether the gripper is more probably a problem when an issue is identified). In accordance with further aspects, the system may employ a contact sensor, such as a magnetic field sensor, in the gripper to detect when there is contact between the gripper and the object by detecting if the position of the compliant tube that the suction cup is mounted to has changed with respect to the rest of the gripper body. This also prevents lip curl due to the high flow that could prevent the generation of a good seal. Further, the suction cups are interchangeable with a tool changer. In particular, the system supports changing the tooltip via a quick tool changer, and the gripper should be designed to withstand the ejection force of the inrush of air against the tooltip's bellows, as well as the decompression of the gripper when the compliance is coupled to the vacuum source. The sensor detects the presence of a suction cup at the end of the tooltip of the gripper, where the suction cup is mounted.
The design of the valving system supports a 100% duty cycle for the blower: the blower can be always on, and the valves enable on-off vacuum switching at the suction cup. But the design may also support idling the blower to improve energy efficiency. Most VFDs have a coast mode that turns off the power to the blower motor but does not actively ramp velocity down to zero. The impeller of a regenerative blower for example, may have considerable inertia and will continue spinning, storing some of the energy as kinetic energy. In this way a system can set the blower to coast in-between picks. There are various ways to implement deciding when to go to coast mode depending on what timing horizon is provided for when the next pick task will be ordered. When no significant timing horizon is provided, a simple timeout can be employed, that is, after the system is idle for a specified period of time the system commands the blower to coast. This is balanced against how early the next pick task is typically known in advance (if it takes 10 seconds for the blower to ramp, but there is only 3 seconds advance notice for a pick, and if pick to pick is typically 15 seconds, then timeout might be 60 seconds, for example, to avoid adding a wait to ramp up before every pick). If longer timing horizons are available, so that pick orders are known 15 seconds in advance, and it takes 10 seconds to ramp, then the system can appropriately plan when to ramp, starting 10 seconds before planned pick.
The pneumatic control system may therefore identify a first period of time between discharge of a first object being grasped and an initial grasp of a second object to be grasped subsequent to the first object; and identify a second period of time that is less than the first period of time during which power to the rotating element is decreased and subsequently increased such that the rotating element returns to the first rotational speed prior to grasping the second object. In accordance with certain aspects, the system may provide, using at least in part a rotating element, a high flow vacuum at the end-effector when the rotating element is rotating at a first rotational speed, identify a first period of time between discharge of a first object being grasped and an initial grasp of a second object to be grasped subsequent to the first object, decrease power to the rotating element for a second period of time that is less than the first period of time, and increase rotational speed of the rotating element prior to grasping the second object. The momentum of the rotating element of the blower may be used to conserve potential energy while reducing energy consumption when not grasping.
The combination of the system being able to change vacuum cup sizes and modulate the vacuum pressure and flow at the vacuum cup provides substantial control over the vacuum grasping system. For example,
With reference to
Generally the gripper will have some compliance so that when it begins to grip an object, there is a low chance of applying too much force to the object via collision. Such a gripper may be either a vacuum coupled gripper or vacuum decoupled gripper.
In a decoupled gripper (
Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the present invention.
The present application claims priority to U.S. Provisional Patent Application No. 63/419,582 filed Oct. 26, 2022, the disclosure of which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
63419582 | Oct 2022 | US |