For a long time, their operation relied entirely on a human army that walked tens of thousands of meters per person per day. This is a very inefficient, expensive, error-prone process. Before the advent of robotic AGV systems, the most advanced solution in this area was to allow employees to ride bicycles in the factory.
Today, warehousing logistics has become one of the largest markets for robotics applications. Among the many logistics robot solutions, the most successful one is Kiva, which was acquired by Amazon for more than $700 million. Thousands of Kiva robots have long been in use, dealing with customers’ massive packages around the clock, far above manual efficiency, lower cost and error rates.
The Kiva robot, which is the core of Kiva’s great success, has been rarely exposed for commercial confidentiality. We don’t know the hardware and software and structural design details that support its powerful performance. However, Ben Einstein, the founder of venture capital firm Bolt, got an old version of the Kiva robot and disassembled it and posted it on the company’s blog. From the details, we can see the crystallization of Kiva engineers’ extensive engineering thinking and experience.
Kiva deploys a QR code every 1 meter on the floor of the warehouse, and Kiva locates them based on these markers. Each of its actions comes from instructions in the cloud. After it reaches the bottom of the target shelf, it uses a delicate ball screw lift structure that raises itself by rotating it in place, lifting the shelf about 10 cm.
What Kiva robots do sounds simple. But you have to realize that a shelf tends to hold up to half a ton of cargo, and a warehouse center usually has tens of thousands of shelves, hundreds of robots, and dozens of incoming shipments. In such a complex and dense system, it is necessary to ensure that the robot does not collide. If any robot collides and falls down the shelf, the damage will be enormous.
How can Kiva robots be so reliable? Let’s take a look at Ben Einstein’s side.
1 system architecture and mechanical structure
From the outside, the Kiva robotic enclosure has an infrared sensing array on each side and a pneumatic bumper for detecting and buffering collisions. There is also a charging port and a series of status indicators on the housing.
Each Kiva robot has three independent degrees of freedom: two drive wheels, plus a rotating motor for lifting. When the hoisting motor rotates, the two drive wheels rotate in the opposite direction. As a result, the tray does not rotate relative to the ground and only rises under the action of the ball screw. Compared to traditional large-load linear drive solutions such as hydraulic and scissor lifts, Kiva’s use of wheels is structurally It is simpler and more reliable.
Left: Kiva inside structure seen after opening the casing. The figure shows the infrared array on the housing, the wireless module, the heavy structure and the lifting motor.
Right: Kiva top view. You can see the lifting structure and the battery.
Each infrared sensor is equipped with an independent filter chip that communicates via a serial bus. In the picture you can see the motor and the giant gear used in the lifting module. Four lead batteries are installed near the bottom of the robot.
2 outer casing
The orange streamlined plastic case is vacuum molded with ABS material. There are a large number of secondary processed structures on it. The vacuum shaping machine and CNC milling used to make Kiva must be huge. This version of the Kiva case is both complex and costly, and the new version is expected to be fully injection molded.
3 collision sensor
For a large streamlined casing like Kiva, it is very difficult to make a traditional integrated collision sensor. Kiva engineers found a very clever low-cost solution: inflating with an ethylene/rubber tube, plus a simple air pressure sensor. Once the change in air pressure in the tube is detected, the robot immediately stops all motion. The black box on the right side of the figure above is used to detect the pressure signal and all infrared sensor signals to simplify the protocol and wiring to the main controller.
4 lifting mechanism
Gearbox, lifting motor and large diameter ball screw
The lifting mechanism uses a custom ball screw that is connected to the motor via a standard nylon gear. The motor used in the lift and the two drive wheel motors are the same Pittman motor. It is capable of outputting about 3N*M of torque and 1KW of stalling power. The motor output shaft passes through a 25:1 Japanese gearbox and can output 46 N*M of torque at 72 rpm. This gearbox costs as much as $1,000, and it would be a lot cheaper if you order a lot.
5 chassis and drive wheel
After removing the lifting structure, we can turn the robot upside down to see the drive on its chassis. The two motors are identical to their gearboxes and lift motors, and the two custom wheels form a differential structure that can be rotated in place.
Three sand cast aluminum parts form the majority of the robot chassis. They are connected by simple U-shaped pins to form a simple passive double suspension structure. Similarly, these aluminum parts are made of 319 alloy, as well as the process of casting and refinishing. Note the heat dissipation structure machined on the chassis in the figure below, which is mounted on the back of the giant MOSFET of the motor driver. This structure can naturally utilize the chassis for maximum heat dissipation efficiency.
Connect the U-shaped pin of the suspension structure to the heat sink on the chassis.
6 electronic components
The design of electronic devices is a very important part of the Kiva robot’s three high-power motors and one-sensors working reliably for a long time.
Battery harness, charging port (top view and side view)
The entire system’s energy comes from four series connected 12V, 28Ah lead batteries. Two of the four batteries are also fitted with thermocouples to ensure they do not overheat. When the battery is too low, the robot will automatically leave the command from the central controller and return to the charging station to charge itself. The design of the charging station leaves a large margin of space to ensure that the robot can be properly charged.
7 camera and imaging module
Look at the camera up and down the net. Both are mounted inside the ball screw.
Placed inside the lifting mechanism is one of the key devices of the Kiva system: a custom dual camera imaging module. One camera looks down at the ground to identify the 2D bar code on the warehouse floor, and the other looks up at the bottom of the shelf. Each camera is equipped with 6 red LEDs for illumination. Sandwiched between the two cameras is an image processing module, the core of which is the ADI ADSP-BF548 Blackfin multimedia processor, which acquires data through a high-speed serial port for data matrix detection.
8 motherboard and daughter board
The overall logic is the main logic module in the above figure. The motor drive board is powered by the battery’s 48V DC; all of the logic components use a single filtered power supply. The driver board for the three-phase brushless DC motor (BLDC) is also fully customizable and is driven by a Lattice LFXP6C FPGA (hidden under the motherboard). All three motor drives are equipped with a current sensor (note: so it is likely to be FOC control), an encoder and six full-bridge MOSFETs (cooled through the chassis).
The daughter board of the FPGA is responsible for coordinating the wireless module, imaging unit, emergency braking, connecting infrared/pressure sensors, power management and motor drivers, greatly reducing the stress on the motherboard. The MCU is a 32-bit, 400MHz Freescale MPC5123, most likely running PowerPC Linux. Two Ethernet ports are connected to the wireless module and firmware storage, which are switched by a Mircel KSZ8993.
The only off-the-shelf electronic component of the entire robot is the communication module: the Soekris Engineering Net4526 dual-antenna router running a single Winstron NeWeb CM9 wireless module connected to the motherboard via Ethernet.
9 can be called the artifact lifting module
This generation of Kiva has a lot of design and is very exquisite, and the most outstanding one is the lifting module. It must be able to lift and lower under a thousand pounds (about half a ton) of pressure and be perfectly parallel to the ground – this is the ideal task for ball screw construction. Usually the ball screws seen on the market are solid, the thickest is only five centimeters, and Kiva custom made this outer diameter of 28 cm, and is a hollow, internal thread structure.
The two housing bearings of the lead screw are all aluminum, and like the chassis are castings that require secondary machining. Both parts are surface oxidized, which provides excellent lubrication and rust resistance for the bearings. The inner casing is fixed, which is equivalent to a spherical nut, and has an injection-molded annular structure on the outer side for restraining the ball; the inner side is in contact with the ball when rotating, and the outer side is connected with the lifting motor through the gear.
Depending on the complexity of the process, the cost of the entire lifting structure is estimated to be around $1,000.
Kiva Systems is one of the few companies to be able to cleverly integrate complex hardware and software into a seamless solution, and has built a system that can dramatically change our buying, selling and lifestyle.
Obviously, Kiva Systems has a very strong hardware engineer, which may be an important reason for Amazon to throw a $775 million price for the acquisition of Kiva in 2012. This article only discusses the robot body, but note that this is only a small part of the entire Kiva solution!