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Smart Position Motor System

Low power consumption, reduced size and weight

Ricoh has developed a DC motor control technology to achieve low power consumption and reduced size and weight, without losing the functions and performance of a conventional stepping motor; it is mounted on Aficio MP C5502 color MFPs, released in 2012.This technology solved the problems of losing steps, high-frequency noise and subsonic vibration inherent in stepping motors; it also significantly lowers the rise in motor temperature. Its immunity to losing steps made it possible to achieve free movement of the motor.

  • The results of replacing two conventional stepping motors (1, 2) with DC motors

image:Results of DC motors mounted on full color MFP
Figure 1. Results of DC motors mounted on full color MFP
*Power consumption: Power consumption (Wh) for a week, based on the measurement under International ENERGY STAR Program

Features of various motor systems compared

Heretofore, Ricoh has employed the following motor types. Brushless DC motors have favorable features in efficiency, weight and size compared with stepping motors. The brushless DC motor, however, requires a sensor and feedback control to achieve the positioning function.

When driving a stepping motor by open-loop control, the output current must be set allowing a large safety margin against actual mechanical load torque so as to avoid losing steps. This causes a significant power loss.

Ricoh has developed a new brushless DC motor control system.

image:Characteristics of motors Ricoh has adopted in the past
Table 1. Characteristics of motors Ricoh has adopted in the past
(Note: Stepping motor is driven at a constant-current and by open-loop control)

Single-motor drive control system

The following introduces characteristics of the brushless DC motor with integrated encoder for position control. Characteristics of its drive system are included.

1. Characteristics of the new brushless DC motor

  • Motor-integrated structure in which encoder sensor and motor driver are mounted on motor substrate
  • An inner rotor type DC motor improves acceleration, deceleration and positioning performance, achieved by reducing inertia and cogging torque.
  • Output of 400 pulses/rotation: 45LPI, output of 100 pulse sensor multiplied by 4
  • Centralized motor specifications such as commonality in winding specifications and shape, and interface compatibility.

2. Development of high speed digital control algorithm

We adopted a low price microcomputer for the control circuit, but included our unique control algorithm firmware, which achieves high precision control. 

Further, we focused closely on safety, including a fail-safe algorithm.

Up to four control parameters can be set, also taking into account the intensification of control ICs.

3. Command signal interface compatible with conventional stepping motors

Interface compatible with pulse (clock) input type stepping motor driver is available, which allows evolution to models with minor changes without changes to the host system.

image:Stepping motor and DC motor driving system compared
Figure 2. Stepping motor and DC motor driving system compared

Multi-motor drive control system

We have developed a multi-shaft control system, which can simultaneously control multiple motors independently. The system is mounted on RICOH MP C8002/C6502 series and RICOH MP C6003/C5503/C4503/C3503/C3003 series color MFPs released in 2013, and their successor products. The system is also mounted as paper feed motors on their peripherals such as document feeders, finishers and large capacity trays.

1. Development of multi-motor drive control system

In order to respond to the need of a new control system to control multiple motors simultaneously, while conventional system controlled every motor with each microcomputer, we have developed two kinds of custom control ICs, five-motor control type and eight-motor control type. This enabled to deploy energy and resource saving effect, the feature of smart position motor, also to the models adopting multiple motors, and to achieve bigger energy and resource saving effect at low cost.

2. Features of multi-motor drive control system

  • Multiple motors can be controlled independently and simultaneously. (The movie attached below shows an example of four-shaft drive).
  • Employed command input system for the command of motor movement. A series of profile generation: acceleration, constant velocity, deceleration and stop, and follow-up control can be executed by one command.
  • Newly develop and mount a high speed digital control algorithm, with further improved position and speed follow-up capability from single-motor microcomputer control
  • Improved performance of encoder counter, making it possible to cope with high-speed rotation or high resolution encoders.
  • By obtaining logging data of motor operating conditions, evaluation and analysis can be performed on a single PC. It will make a significant contribution to product development efficiency (shorten development period, reduce development man-hours)

image:Multiple-motor control system by multiple smart position motors
Figure 3. Multiple-motor control system by multiple smart position motors

image:Custom control ICs: eight-motor control type (left) and five-motor control type (right)
Figure 4. Custom control ICs: eight-motor control type (left) and five-motor control type (right)

Movie of brushless DC motor (multi-shaft behavior)

Brushless DC motor with encoder-less position sensing function

Ricoh developed a driver IC for a brushless DC motor that enables encoder-less detection of rotational position, and developed an inner-rotor brushless DC motor with the driver IC installed. The driver IC and the motor were first mounted on the RICOH MP6054/5054/4054 series and RICOH MP3554/2554 series of digital monochrome MFPs released in October 2014. They were then mounted on their successors, the RICOH MP6055/5055/4055/3555/2555 series of digital monochrome MFPs released in January 2017, and on their peripherals.
With digital color MFPs, the driver IC and the motor were mounted on the RICOH MP C6004/C5504/C4504/C3504/C3004 series released in May 2016 and on their peripherals.

1. Driver IC for brushless DC motors with encoder-less position sensing function

Ricoh has developed a driver IC for brushless DC motors, which generates encoder signals from Hall element signals. In the past, a position detecting sensor such as an encoder and a motor driver IC were two separate parts. Their functions are now integrated on a single motor driver IC to save space, reduce cost, and increase environmental robustness. Motors featuring this driver IC are now usable in environments where optical encoders pose a concern. The energy and resource conservation effects of the smart position motor system are now available for many more products and models at a low cost.

Comparison of constructions (left: brushless DC motor with optical encoder, right: encoder-less brushless DC motor)
Figure 5. Comparison of constructions (left: brushless DC motor with optical encoder, right: encoder-less brushless DC motor)

2. Characteristics of the motor driver IC

  • The rotational position sensing function and the brushless DC motor pre-driver function are integrated on a single chip.
  • No new sensor is required; rotational positions are detected with a conventional Hall element.
  • Even though the rotational position sensing function has been added, the driver IC is no larger than the conventional pre-driver IC (5 mm × 5 mm).

image:Newly developed motor driver IC (left: RN5C711, right: RN5C772)
Figure 6. Newly developed motor driver IC (left: RN5C711, right: RN5C772)

3. Advantages

  • The brushless DC motor does not have an optical encoder, so it has excellent environmental robustness against dust, paper particles, oil, toner, and ink mist. The robustness contributes to the expansion of motor applications.
  • The absence of an optical encoder allows the upper limit of the motor operating temperature to be higher. The motor can be used under high temperature, and has high thermal tolerance during a continuous drive.
  • The thin motor is possible because it requires neither an optical encoder code wheel nor an encoder sensor.
  • Supported output resolutions are 360 and 720 pulses/revolution. (RN5C771 supports 360 pulses only. RN5C772 gives a choice between 360 and 720 pulses.)